FACTORS AFFECTING ARABIC BREAD QUALITY
Presented as a thesis for the degree of
Doctor of Philosophy
of
School of Applied Bioscience
University of New South Wales
by
Kenneth James Quail
B.Ag.Sc.(Hons), (University of Melbourne, Australia)
December, 1990 DECLARATION
I, Kenneth James Quail, hereby declare that none of the work presented in this thesis has been submitted for a higher degree to any other University or Institution
Ken Quail
ii ACKNOWLEGEMENTS
I wish to thank Dr G. McMaster, Director of the Bread Research Institute of Australia for his guidance, support, and for making the facilities of the Institute available for my study.
My thanks to Professor M. Wootton for his supervision and assistance throughout the period of my study.
I would also like to thank all the staff at the Bread Research Institute for their help, and in particular Ms s. Ormston for technical assistance.
The assistance of Dr M. Dickson with the electronmicroscopy was greatly appreciated.
The support of the Wheat Research Council of Australia for funding this project through the award of a Postgraduate
Fellowship is gratefully acknowledged.
My deepest graditude is for my companion Liz Marles, who has provided me with so much love and support.
iii CONTENTS
DECLARATION ii ACKNOWLEDGEMENTS iii
List of plates X
ABSTRACT xii
1 INTRODUCTION 1
2 LITERATURE REVIEW 5
2.1 Arabic Bread 5
2.1.1 Baladi bread production 7
2.1.2 Automated production of Arabic bread 8
2.1.3 Pocketing of Arabic bread 11
2.2 Test Baking 13
2.3 Bread Scoring 21
2.4 Flour Quality 26
2.4.1 Milling variables 29
2.4.1 Rain damaged wheat 30
2.5 Shelf Life 31 2.5.1 Spoilage 32 2.5.2 Staling 32 2.5.3 Retarding staling 35
iv 2.6 Fractionation and Reconstitution 37
2.6.1 Water-solubles 38
2.6.2 Gluten 39
2.6.3 Starch 40
2.6.4 Flour lipid 40
2.7 Conclusion 43
3 MATERIALS AND METHODS 44
3.1 Amylograph Test 44
3.2 Bread Moisture 44
3.3 Crust and Crumb Colour 44
3.4 Determination of Ash 44
3.5 Determination of Flour Colour Grade 45
3.6 Determination of Falling Number 45
3.7 Determination of Flour Moisture 45
3.8 Determination of Maltose Figure 45
3.9 Determination of Particle Size Index 45
3.10 Determination of Protein Content 46
V 3.11 Determination of Damaged Starch 46
3.12 Flour Samples 46
3.12.1 Flour samples for sections 4.2 and 4.3 46
3.12.2 Flour samples for section 4.4 46
3.12.3 Flour samples for section 4.5 47
3.12.4 Flour samples for section 4.6 47
3.13 Fractionation and Reconstitution of Lipid 47
3.13.1 Defatting of flour samples 47
3.13.2 Reconstitution of defatted flour samples 48
3.13.3 Sepc;p:-ation of polar and nonpolar lipid 48
3.13.4 Reconstitution of lipid fractions 48
3.14 Measurement of Starch Gelatinization Using
Glucoamylase 49
3.15 Microscopy 49
3.15.1 Light microscopy 49
3.15.2 Electron microscopy 50
3.16 Mixograph 50
3.17 Physical Dough Testing 51
3.17.1 Farinograph 51
3.17.2 Extensograph 51
3.18 Test Baking 51
vi 3.18.1 Test baking of Arabic bread 51 3.18.2 Scoring of Arabic bread 52 3.18.3 Test baking of Pan bread 55
3.19 Fractionation and Reconstitution of starch,
Gluten and Water-solubles 55 3.19.1 Fractionation of starch, gluten and water-solubles 55
3.19.2 Reconstitution of starch, gluten and water-solubles 56
3.20 Statistical Analysis 56
3.21 Test Milling 57
3.22 Thin Layer f.:hromatography (TLC) 57
3.23 Varietal Identification 57
3.24 Water Activity 57
3.25 Wheat Samples 58
3.25.1 Wheat samples for section 4.5 58 3.25.2 Wheat samples for section 4.6 58
4 RESULTS AND DISCUSSION 59
4.1 Importance of Arabic Bread to Australia 59
4.1.1 Australian wheat exports to the Middle East 59 4.1.2 Australian consumption of Arabic bread 60 4.1.3 Conclusion 62
vii 4.2 Scoring System for Arabic Bread 62
4.3 Effect of Baking Temperature/Time Conditions and Dough Thickness on Arabic Bread Quality and Test Baking Method 66 4.3.1 Effect of baking temperature/time conditions and dough thickness on Arabic bread quality 68 4.3.2 Comparison of test baking methods 76 4.3.3 Comparison of test baking method with a commercial bakery 82
4.4 Effect of Baking Conditions and Dough Thickness on the Starch Gelatinization and Bread Structure of
Arabic bread 87
4.4.1 Light microscopy 87
4.4.2 Starch gelatinization 93
4.4.3 Electron microscopy 94
4.4.4 General discussion 101
4.5 Flour Quality Tests for Selected Wheat Cultivars and Their Relationship to Arabic Bread Quality 106
4.5.1 Correlation matrix 107 4.5.2 Multiple regression 110 4.5.3 Arabic bread and flour protein content 110
4.5.3.1 Within cultivars 110
4.5.3.2 Between cultivars 113 4.5.3.3 Combined sample set 115
viii 4.5.4 Pan bread and protein content 115 4.5.5 Grain hardness 117 4.5.5.1 Soft wheats 117 4.5.5.2 Hard wheats 117 4.5.5.3 Correlation matrix for hard grained wheats 118 4.5.5.4 Flour quality parameters 119
4.6 Role of Flour Components for Arabic Bread 121
4.6.1 Role of flour lipid 122
4.6.1.1 Baking absorption 122 4.6.1.2 Reconstitution of flour with parent lipid 123 4.6.1.3 Bread quality of reconstituted lipid fractions 128
4.6.1.4 Addition of soy oil to defatted flour 129
4.6.1.5 Addition of wheat lipid and soy lipid to whole flour 130
4.6.1.6 Exchange of lipid fractions between flour samples 130
4.6.1.7 TLC 131
4.5.2 starch, gluten and water-solubles 133 4.6.2.1 Role of water-solubles 134
4.6.2.2 Role of starch and gluten 137
5 CONCLUSIONS 146
6 APPENDICES
Appendix 1 153
Appendix 2 154
Appendix 3 157
Appendix 4 158
7 BIBLIOGRAPHY 159 ix List of Plates
4.1 Photomicrograph of cryostat section of the top layer of Arabic bread, baked with a dough thickness of 1.5mm at 400°c for 90 sec. Stained with Ponceau 2R and viewed under crossed polars and a quarter-wave plate.
4.2 Photomicrograph of cryostat section of the top layer of Arabic bread, baked with a dough thickness of 1.0mm at 400°c for 90 sec. Stained with Ponceau 2R and viewed under crossed polars and a quarter-wave plate.
4.3 Photomicrograph of cryostat section of the top layer of Arabic bread, baked with a dough thickness of 1.5mm at 600°C for 21 sec. Stained with Ponceau 2R and viewed under crossed polars and a quarter-wave plate.
4.4 Photomicrograph of cryostat section of the top layer of Arabic bread, baked with a dough thickness of 1.0mm at 600°C for 21 sec. Stained with Ponceau 2R and viewed under crossed polars and a quarter-wave plate.
4.5 Scanning electron micrograph (S.E.M.), cross section of the upper layer of Arabic bread baked with dough thickness of
1.00mm at 600°C for 21sec.
4.6 S.E.M. cross section of the upper layer of Arabic bread baked with dough thickness of 1.00mm at 400°C for 90sec.
X 4.7 S.E.M. crust surface of the upper layer of Arabic bread baked with dough thickness of 1.00mm at 400°C for 90sec.
4.8 S.E.M. cross section of the crust of the top layer of
Arabic bread baked with a dough thickness of 1.00mm at 600°c for 21sec.
4.9 S.E.M. internal surface of a crumb cell, adjacent to the crust, the upper layer of Arabic bread baked with dough thickness of 1.0mm at 600°C for 21sec.
4.10 S.E.M. internal surface of a crumb cell near the
interior surface of the upper layer of Arabic bread baked with dough thickness of 1.0mm at 600°C for 21sec.
4.11 S.E.M. cross section of the upper layer of Arabic bread
baked with dough thickness of 1.5mm at 400°C for 90sec.
4.12 S.E.M. crumb cells adjacent to the crust of the upper layer of Arabic bread baked with dough thickness of 1.5mm at
400°C for 90sec.
4.13 S.E.M. crumb cells near the interior surface of the
upper layer of Arabic bread baked with a dough thickness of
1.0mm at 400°C for 90sec.
4.14 Thin layer chromotograms of wheat flour lipid, polar
lipid, nonpolar lipid and soy lipid.
xi ABSTRACT
Factors affecting Arabic bread, which is a round two layered flat bread, were studied. These included the effect of processing variables, and wheat and flour quality parameters.
A new scoring system for the evaluation of Arabic bread is presented which allows discrimination between flour samples. This system is suitable for the evaluation of bread in commercial bakeries.
Dough thickness and baking temperature/time conditions were varied: doughs sheeted to less than 3.0mm thick, required baking temperatures higher than 500°C, whilst doughs thicker than 3.00mm benefited from temperatures lower than 500°C. Thinner doughs baked at higher temperatures for shorter times produced bread with better keeping quality.
The processing variables identified as being optimal in this study were incorporated into a test baking method. This method gave reproducible results and greater discrimination between flour samples than a previous method.
Microstructure and starch gelatinization of Arabic bread was examined. A thin layer of ungelatinized starch on the upper surface formed the crust, the thickness of this layer varied with both dough thickness and baking temperature. The majority of the crumb starch was gelatinized, with minor differences occurring in the extent of gelatinization and the
xii structure of the crumb, again resulting from dough thickness and baking temperature/time treatments.
Analytical and rheological parameters were established for
flours from nine selected wheat cultivars covering a range of
protein contents for each. Arabic and pan breads were baked from these flours and baking quality was determined.
Wheat cultivars were found to differ in their suitability for Arabic bread production. Within cultivars the relationship between protein content and Arabic bread score was best
described by a quadratic equation.
Traditional flour quality tests do not adequately describe the flour quality requirements for Arabic bread as clearly
as for pan bread. Ranges and optimum values for a number of
parameters were established to describe flours most likely to be suited to the production of Arabic bread. However for
reliable evaluation of baking quality for Arabic bread,
flours fitting the prescribed range must be test baked.
Fractionation and reconstitution techniques were used to
study the function of the lipid, starch, gluten and water
soluble fractions of wheat flour in Arabic bread. Wheat lipid
was found to be important for the stabilization of the
expanding cell structure during baking, however this fraction
did not account for the differences in baking quality of the
samples tested.
xiii Exchange of the gluten and starch fractions between three flour samples revealed that starch from the cultivar Hartog accounted for the superior keeping quality of Arabic bread baked from this cultivar.
Sections of this study have been accepted for publication and
are currently in press, whilst other work has been recently
submitted for publication (Appendix 4).
xiv 1 INTRODUCTION
A large proportion of Australia's wheat is exported to the Middle East. This wheat is mostly used for the production of flat breads, of which Arabic bread (a round two layered flat bread), is the most common. Originally baked manually this bread is increasingly being produced in fully automated bakeries. Arabic bread has recently become popular in countries outside the Middle East including Australia.
Little information is available on Arabic bread and its production when compared to the wealth of publications on pan bread. New information on the factors affecting Arabic bread quality could be used to assist bread manufacture in the Middle East, export of Australian wheat to the Middle East, and the growing domestic Arabic bread industry in Australia.
In order to investigate the factors affecting Arabic bread quality, both a scoring system and a test baking method are required. These should provide reproducible results, allow differentiation between treatments, and be representative of commercial practice and consumer preference. A number of studies have described scoring systems (Faridi and Rubenthaler, 1984; Qarooni et al., 1987; Williams et al., 1988). The test baking method of Qarooni et al. (1987) was developed by examining and optimizing processing variables. This is seen to represent the approach of
1 commercial practice, where the aim is to produce a consistent product of good quality.
Processing conditions for the commercial production of Arabic bread may differ between bakeries. For example, dough thickness is largely selected for consumer preference and the baking temperature/time conditions are often governed by technical constraints. No studies have been published on the interaction of these variables.
Flour samples of different quality have been compared for
Arabic bread production (Qarooni et al., 1988; Williams et al., 1988), and general descriptions of flour quality suitable for Arabic bread have been made. There have not been any studies published examining the effect of flour protein content within wheat cultivars or comparing cultivars for their suitability for the production of Arabic bread.
Fractionation and reconstitution techniques have been used to identify the role of individual fractions in the baking of ~. . pan bread (McR1tch1e, 1982). This has led to the ) identification of specific protein groups which are associated with flour of optimal pan bread baking quality
(Singh et al., 1988).
By studying the contribution of individual flour components to Arabic bread quality, it may be possible to understand the differences between wheat cultivars and, hence to create selection criteria or wheat breeding objectives. No studies
2 concerning the relationship of flour fractions to the baking of Arabic bread have been published.
In an attempt to address the points discussed so far, the aims of this study are:
1) To establish the importance of this product to the Australian economy.
2) To evaluate published scoring systems and improve on them if possible.
3) To examine the interaction between dough thickness (measured immediately after dough rolling), and baking temperature and time conditions, and to apply this information to the following: effect on bread quality, test baking method, starch gelatinization and bread microstructure.
4) To establish the influence of protein content within wheat varieties on Arabic bread quality.
5) To establish whether there are differences between wheat varieties in their suitability for Arabic bread.
6) To define the use of traditional flour tests for the assessment of flour for Arabic bread production.
7) To examine the role of the lipid, starch, gluten and
3 water-soluble fractions in the baking of Arabic bread.
8) To identify flour factors responsible for varietal differences in quality for Arabic bread production.
9) To interpret data in terms of improving the keeping quality of Arabic bread.
The study of scoring systems and test baking methods will be useful for further research on this product. Results from the study on dough thickness and baking conditions will be useful for commercial bakers and the manufactures of bakery equipment. Information on wheat varieties, and the relationship of traditional flour tests to Arabic bread will be useful for wheat breeding programmes, and wheat and flour marketers. The information on flour fractions will be most useful to wheat breeders. Any information on improved keeping quality would be a potential advantage to the whole industry.
4 2 LITERATURE REVIEW
2.1 Arabic Bread
Arabic bread is a round two layered flat bread baked from a fermented dough. This style of bread originated in the Middle East, where a number of different breads fitting this description are consumed. A list of breads included under this definition is presented in Table 2.1.
Table 2.1 List of bread names used to identify round two layered flat breads.
Author Bread name
Avita! and Mannheim {1988) Pita,Flat,Pocket,Baladi
Dalby (1963) Ballady
Moses {1981) Sharmie,Arabic,Lebnarni,Mayar, Sharwma,Mafrood,Kmag,Tamis, Manfok,Balady,Egypie,Burrd, and Lahuh
Mousa and Mohizea (1979) Mafrood and Burr
Qarooni {1988a) Baladi,Halabi,Lebanese,Arabic, Bouri,Bairuti and Souri
The number of names used for this bread results from the following:
5 1. Different regions have developed distinct breads, these vary in diameter, weight, thickness,extraction of flour and moisture content. For example, Lebanese bread is made from
white flour and is baked as a very thin (3 - 5mm) product
with a large diameter (300 - 400mm) compared to Burr from Saudi Arabia which is made from flour of high extraction, is
thicker (10 12mm) and has a smaller diameter (200 240mm).
2. Different names may be used to describe the same product, for example sharmie, mafrood and pita all refer to a bread
made with white flour, of intermediate thickness (8 - 12mm) with diameter ranging from 150 - 200mm.
3. Phonetic spelling in English of Arabic names has resulted
in different spelling of the same name, for example, baladi, balady and ballady all refer to the same product.
Because of the number of bread types and names, it is important to define the bread to be studied and to use consistent nomenclature. For example: Avital and Mannhein
(1988), interchanged the term "flat bread" for Arabic bread This is ambiguous without further description for there are many flat breads that do not have two layers and are quite different to Arabic bread. For this study Arabic bread is defined by both its description and method of production.
Egyptian baladi bread is different to the other breads
6 listed in Table 2.1. It is baked with a high water addition and this results in a slack dough that has not been successfully handled with automated equipment. The sheeting and final proofing stages present the major difficulties. This contrasts to the other breads, which are made with a dry dough, such that the sheeting to thin dough pieces and subsequent proofing of these pieces can be achieved with automated equipment. This study will focus on Arabic bread produced under automation as this requires a greater understanding of the factors affecting bread quality. However, the production of baladi bread in Egypt will be discussed initially, as it provides a background for looking at the development of Arabic bread.
2.1.1 Baladi bread production
Although Baladi bread production accounts for up to half the flour consumption in Egypt,it is still baked by hand. The description of production by Dalby (1963) is similar to that of Qarooni (1988a) and both have been confirmed by visits to several bakeries in Egypt by the Author in 1990.
A high extraction flour with clearly visible bran flakes (100 parts) is mixed with salt (0.5 to 1.0 parts),water (70 to 75 parts) and starter (either old dough or a flour and water ferment). Mixing is of low intensity and there is little gluten development. After mixing, the 'slack' dough is allowed to stand for approximately 20 min in the mixing bowl. Dividing is done by hand and scaled dough balls are deposited
7 in boxes dusted with bran. After lOmin the dough piece is patted flat, after a further 15min the dough is baked. As the dough is removed from the proofer box it is flattened further, and stretched by hand to give a diameter of approximately 200mm for a 200g dough piece. An oven peel is used to place the dough on the oven hearth for baking at approximately 350°C for two min. When the product is cooled it can be either flattened and sold as balidi tarri (soft baladi), or it can be baked again at approximately 200° c for 2 min to produce a dry brittle bread known as baladi meladin (dry balidi).
2.1.2 Automated production of Arabic bread
Traditionally Arabic bread was made manually in small local bakeries and was purchased and consumed within hours of baking. Whilst this form of production still exists in some regions, in the last 10 to 15 years there has been a swing to centralized production in fully automated bakeries in many countries.
The following description of automated production of Arabic bread has been compiled after visits to bakeries in several different countries and confirms that of Qarooni (1988a).
Ingredients: The bread is typically produced from a simple formula of flour (of variable extraction), salt, yeast and water. Sugar and oil may also be included in the formulation but are not necessary. It is unusual to see the use of any
8 additional ingredients or the use of bread improvers.
Processing: An outline of an automated bakery is presented in Figure 2.1. A brief description of each step in the process follows. It should be acknowledged that this is a general description and many variations exist in industry.
Figure 2.1 Diagram of a fully automated Arabic bread bakery.
mix round first sheeting divide proof rolls
final proof
cooling and oven packaging
The ingredients are mixed to produce a fully developed dough which is quite 'tight' due to low water addition. A fermentation period follows after which the dough is transferred to a divider. The dough is then divided and rounded. There is a short intermediate proof of approximately 10 min before sheeting. An illustration of the sheeting process is shown in Figure 2.2.
9 The first roller gap is approximately 10mm. The second sheeting which is in the same direction is more severe with a roll gap of approximately 2mm. A third sheeting of the flattened, oblong dough piece is made at right angles to the first two. This gap is set to roll the oval dough into a circular piece of desired thickness. (Actual roll gaps will depend on the specific circumstances of production.)This process requires that the dough does not stick to the rolls.
It should be noted here that some bakeries are using dyes to cut the bread shape from a continuously sheeted dough. Many shapes of bread are possible using this system, however this method of production will not be discussed in detail.
Figure 2.2 Diagram of the sheeting process for Arabic bread.
o~ C) ) c__ J dough
first rolls second rolls l
third rolls
The sheeted doughs are passed through a multiband final proofer on a conveyor belt system arranged so that each dough piece travels along a conveyor section and is dropped onto
10 the belt below. After a proof of 20 to 30 min, the dough is baked at high temperatures ranging from 400°C to 650°C for corresponding times of 90 and 15sec. During baking the bread separates into two layers. After baking the bread is cooled and flattened before packing.
2.1.3 Pocketing of Arabic bread
Pocketing is the process by which the two layers are formed during baking. Faridi and Rubenthaler {1983), described this for Baladi bread and stated that "a crust forms in less than 1 min and the internal temperature reaches a point high enough to develop steam that puffs the bread... Thus leavening is due considerably to steam". This is an inadequate explanation and yet this and similar descriptions have been used by other authors (Dalby, 1963; Mousa et al., 1979).
Williams et al. (1988) provided the following description of pocketing for Arabic bread: "the millions of gas bubbles that have reformed after sheeting expand very rapidly (in the oven) causing the dough to inflate to a balloon-like appearance. When the balloon bursts under the pressure of the expanding gases inside, the top half collapses onto the bottom half to give the two layers". Further to this Williams and El-Haramien (1989) have stated that for Arabic bread, pocketing is due to"expansion of carbon dioxide bubbles" and that for Baladi bread "the ballooning effect is caused by expansion of steam".
11 No specific evidence was presented to support these statements and they appear to differ from this author's experience. For instance, the observation that "when the balloon bursts ... the top half collapses" is different to that observed for many bakeries, where the expanded structure caused by the pocketing is retained until the product has cooled to ambient temperature or in some cases, is physically flattened for packaging.
For pan bread the rapid expansion of fermentation gases results in what is referred to as oven spring(Baker and Mize,1939). Williams et al. (1988}, made no attempt to explain why the same phenomenon should result in a separation of layers for Arabic bread.
Mizrahi and Mizrahi (1988} have attempted to describe pocketing in more detail. Again no evidence is provided however they have followed the stages of baking, have applied general principles and made observations of the baked product. A summary of their description of pocketing for Arabic bread follows:
Firstly the outer surface of the dough forms a skin,then as the internal temperature rises, fermentation gases expand and open out the cell structure formed during proofing periods. Steam is also generated which along with the fermentation gases disperse through the open crumb structure. Then "as a result of the temperature gradient and drying, the weakest
12 tissue is in the centre plane. Once the steam pressure inside the pita is high enough to overcome the cohesive forces at this point, detachment into the two separate layers takes place".
This was the best description of pocketing available. It is expected that further study of this product will lead to a more accurate account of the process.
2.2 Test Baking
Test baking methods provide a means of examining individual variables in the baking process, for example, in evaluating the baking quality of flour. A test method should relate to the commercial production targeted, use small sample size, and provide reproducible results.
For pan bread, there are many test baking methods. This is because commercial production techniques vary and methods have been developed to suit different procedures. The AACC method is based on the American sponge and dough system. The method of Bond and Moss (1983) represents the no time dough process of Australia and the method described by Larson et al. (1986) is designed for the mechanical dough development used in New Zealand. It has been demonstrated that different methods can rank flour samples differently (Tipples, 1979). This highlights the need to relate the test method to a
defined commercial process.
13 Baking methods for Arabic bread are not well established, as few studies have used previously published methods and there have been no collaborative baking tests reported.
Malaki and Daghir (1967) developed a test baking method for Arabic bread for the investigation of vitamin retention. A basic formulation of flour (100 parts), water (55 parts), salt (1.25 parts) and yeast (0.75 parts) was used. A dough based on one kg of flour was mixed in a Crypto mixer for 12 min. After 8 min. rest, the dough was divided, each piece was rounded and then fermented for 10 min. Next, the dough was rolled to a thickness of 4 mm fermented for 45 min. and baked at 400°C, 450°C and 5oo·c. The method did not specify fermentation temperature, humidity level,or mention whether these conditions were controlled.
Hallab et al. (1974) used a similar method with water addition determined by a dough consistency of 800 BU measured on the Farinograph. Although this was a nutrient retention study, for which the baking time and temperature are considered important elements, the report did not include details of either parameter.
An instrument for rolling doughs to a measured thickness was presented for inclusion in the test baking method of Rubenthaler and Faridi (1982). This instrument was used to investigate the ideal dough thickness for Arabic bread. The dough is placed on a template and rolled flat with a rolling
14 pin. This action of rolling is very different to sheeting rolls described elsewhere (Qarooni et al., 1987; Williams et al., 1988). It is also different to the rolls used by commercial bakeries (Freimann, 1980; Cooper, 1986; Kroskey,
1988). Adjustable rolls for dough are easily obtained and give accurate control of dough thickness.
Faridi and Rubenthaler (1984a) used the test baking method of
Rubenthaler and Faridi (1982) including the specialized dough roller. This was applied to the evaluation of optimal water absorption, shortening level and baking conditions. Dough was prepared with the following formula: flour (100 parts), salt
(1.5 parts),yeast (l.O part), ascorbic acid (50ppm) and malted barley (0.25 parts). Water addition levels of 47,57 and 67 parts were tested. A well developed dough was mixed and fermented for 30 min at 95% RH. It was then rolled to a thickness of 3mm, proofed for 45 min. at 95% RH and baked at either 260°C for 4 - 5 min. or 480°C for 90 sec. Inclusion of ascorbic acid in the formula was based on the finding that the addition of 50ppm improved bread quality for a range of flours. However this is inconsistent with the other methods referred to in this review where in all cases, no ascorbic acid was included. A study by Qarooni et al. (1989a) of the effect of additional ingredients tested Ascorbic acid at 50,
70 and 100 ppm. Bread quality was found to decline with each increase in the level of ascorbic acid. Mizrahi and Mizrahi
(1988) found that at 75 ppm, bread quality was adversely affected.
15 Faridi and Rubenthaler (1984a) found that the highest water addition of 67% , gave the best quality bread. This differs from their earlier work of 1983, where the same method was applied except that water addition was based on a Farinograph dough consistency of 800 BU. For a range of flours the highest level of water at 800 BU was 56%.Both Qarooni et al. (1987) and Williams et al.(1988) found that the limiting factor to water addition was dough handling,especially sheeting. It would appear that the specialized dough roller has allowed much stickier doughs to be handled than would be possible in commercial baking where the dough is sheeted through rollers.
It is important to note that little attempt has been made to relate the above methods to commercial practice.
To support a wheat introduction programme for Syria, Jordan and Lebanon, a test baking method has been published by Williams et al. (1988). After surveying the local bakeries, they developed a method which represented an "average" formulation and procedure. The method also uses equipment made to simulate that used in industry, but on a smaller scale.
Based on the handling characteristics of the dough, water absorption was optimized at 4 - 8% below the farinograph absorption. Sheeting was performed with commercially available rolls, which were adjusted for each dough to give the appropriate dough thickness. Sample size required 600g of
16 flour and full size loaves of 200g dough weight were baked.
Although Williams et al. (1988) described their method in detail, there is some inconsistency and missing information. In a table which summarizes the baking procedure, the baking temperature is presented as 450 - 470°C with corresponding baking times of 35 - 50 sec. This large difference in baking times suggests that the control of oven temperature is poor. However in the method description, the baking time and temperature is presented as 460± 10°c with a baking time of 40 - 50 sec. The reader is uncertain as to which is correct. Furthermore, no details of the final proof conditions were provided.
Qarooni et al. (1987) described a test baking method for Arabic bread in considerable detail. This method is designed to be representative of automated bakeries. Some features of the method were fixed according to observation of industry, whilst some variables were trialed to give optimal bread quality. Water addition is based on a Farinograph dough consistency of 850 BU, as this was found to give good dough handling and bread quality. This figure is similar to that used by Hallub et al. (1974) of 800 BU and Williams et al. (1988) at 4 - 8 % less than Farinograph water absorption. Typical figures of 54 - 56% water addition result from this dough consistency and this contrasts to the figure of 67% suggested by Faridi and Rubenthaler (1984a). Mixing time was optimal at 1 min past peak Farinograph development, indicating that doughs should be well developed. For
17 sheeting, a set of rolls was used to produce doughs of approximately 3mm thickness. The temperature and humidity at all proof times were controlled, with the final proof at 65%
RH being much lower than that of 95 % RH used by Faridi and Rubenthaler (1984a). A summary of the method of Qarooni et al. (1987) follows: Flour (100 parts), water (850 BU consistency), salt (1.5 parts) and yeast (1.0 part compressed) were mixed to a well developed dough allowed to rest for 1 hour at 30°C, divided and rounded by hand, proofed for 10 min at 30°C, sheeted to approximately 3.00mm thickness, proofed at 30°C and 65% RH for 30 min before baking at 400°C for 90 sec.
A method based on that of Qarooni et al. (1987) was used by Cornish and Palmer (1988). The only modifications were to the baking absorption, measured at 800BU rather than 850 BU,and the baking conditions of 450°C for 80 sec rather than 400°C for 90 sec.
Reproducibility of the above baking tests can only be assessed when the bread is evaluated. This is discussed in the following section.
Of the methods described, that of Qarooni et al. (1987) gives the best information for repeating the procedure and is based on optimizing bread quality under similar conditions to automated production.
Other studies of baking variables have been in the context of
18 production rather than test baking. These studies will be discussed as their aim was to investigate product optimization, the results of which could be incorporated into test baking methods.
Mizrahi and Mizrahi (1988) examined the optimization of Arabic bread production using the Chorleywood Bread process. Satisfactory Arabic bread was manufactured with this process in a shorter time than with the conventional straight dough method. Mixing time was shortened and the bulk fermentation time was reduced from 30 - lOmin. To compensate for the shorter fermentation time available, the amount of yeast was increased from 1.5 to 3.0 % and dough temperature was maintained at 30°C. In keeping with the requirements of this process, water addition was increased from 49 to 55%. The advantage of this method is the reduced production time. A further area for investigation would be to examine the effect on flavour as many flavour compounds are believed to be produced by extended fermentation periods. With an appropriate mixer it would be possible to represent this process by the test baking method of Qarooni et al. (1987).
Qarooni (1989a) investigated the effects of fermentation variables. This included the time allowed for bulk fermentation and intermediate and final proofs at a range of temperatures. Adequate fermentation was required for good quality Arabic bread. If the temperature was too low or the final proof too short, blisters appeared on the upper surface, the layers were uneven and the crumb structure was
19 poor. Williams and El-Hareim (1989) investigated fermentation by adjusting yeast levels. Weak and medium strength flours improved in bread quality up to a yeast addition of 1% and strong flour improved up to 2%. Fermentation periods and yeast levels appear to be satisfactory for the test baking methods described.
Information on the effect of other additional ingredients appears to be limited. Qarooni et al. {1989b) studied a range of ingredients including ascorbic acid, the results of which have been referred to previously. They found that potassium bromate at 10, 20 and 30 ppm did not improve bread quality, nor did the reducing agents L-cysteine hydrochloride and sodium metabisulphite. ·., Sodium steroyl lactylate at levels up to 3gkg-l improved bread scores with the most significant effect being improved keeping quality. The highest bread scores were achieved with an addition of both 2.5 gKg-l SSL and 5.0 gKg-l shortening. This work was completed on a single flour sample considered optimal for
Arabic bread production. It would be useful to trial the additional ingredients with other flour samples including those not considered optimal. This would provide information to those manufacturers who are unable to obtain flour of optimal quality. Until such work has been completed, it would appear appropriate to test bake without additional ingredients.
20 2.3 Bread Scoring
Bread scoring systems should provide reproducible evaluations of bread quality. These systems are necessary to compare breads made with different ingredients or processing conditions. They are also useful for quality control programmes.
Tests of quality can be objective, where measurements are made according to a defined procedure, and no judgment on behalf of the operator is required. They may be subjective where the operator applies judgment based on a set of guidelines, in the case of a trained operator, or according to personal preference in the case of an untrained operator.
A scoring system may involve a range of criteria which may be evaluated by either subjective or objective techniques. For reproducible results from systems involving subjective evaluation, the criteria must be clearly defined and the operator(s) trained.
Scoring systems must provide an evaluation that is relevant to both bakers and consumers. This requires the identification of specific criteria and a rating reflecting their relative significance.
For Arabic bread a number of scoring systems have been developed, but as for the test baking methods, these have not been reported to have been trialed in collaborative studies,
21 nor have they been evaluated by independent studies. A number of scoring systems are presented and evaluated.
Faridi and Rubenthaler (1983) combined subjective and objective tests for the evaluation of Arabic bread made from different wheat varieties. An objective test of bread firmness was made with a Fudon Rheometer fitted with an 0.29mm wire that cut through a 1 cm slice of bread. Low values were considered desirable. There were 5 subjective criteria, each scored out of 10. Desirable features were: complete separation of the crusts, and that these were of equal thickness; a soft, white, moist crumb;and a light and shiny crust with brown spots. It should be noted that the same quality description was made for both Arabic bread and baladi, with the exception that baladi should have a darker crust because of the higher extraction flour. In a later publication, Faridi and Rubenthaler (1984a) used a modification of the system described above. The objective test of bread firmness was not used and weightings were applied to the subjective criteria. The criteria and weightings were: crust colour 10, crumb colour 5, upper to lower crumb ratio 20, pocket formation 20 and crumb texture 10. This was presented with the same description of optimal quality as presented in Faridi and Rubenthaler (1983). No explanation was given to support the criteria or the weightings chosen. On the descriptions of the subjective quality criteria, it could be difficult to repeat these assessments.
22 Avita! and Mannheim (1988) used a Precision Penetrometer to make objective evaluation of 'bread texture•. A plunger of 250g was dropped from a height of 3cm above the bread which was placed on a cup of 75mm diameter. This test recorded an increase of bread firmness over time. Differences were measured over periods as short as one hour and the test gave reproducible results. This objective test could be used to evaluate staling of Arabic bread in future studies. They also included a panel of 15 untrained people to compare bread samples. This was a hedonic evaluation with no guidelines other than to rate the bread from best to worst on a scale of 1 to 5. No attempt was made to relate the objective test to the hedonic scores which may have provided further support for the use of the Penetrometer.
Mizrahi and Mizrahi (1988) did not apply a strict scoring system for the comparison of bread samples. They used one objective measure and descriptions of quality features to differentiate samples. The defects of Arabic bread considered most important were: the appearance of dark blisters, non uniform layers and poor separation of layers. A uniform crust colour of golden brown was considered a desirable feature. To assess the uniformity of the layers they weighed each layer and used the ratio of weights as a measure of
quality.
Qarooni et al. (1987) described a scoring system in considerable detail. It includes 16 criteria that are applied with a total of 7 different weightings. Three measurements
23 were made objectively including: area index, which is a measure of bread diameter to assess shrinkage or expansion during baking;and crust and crumb colour measurement using a Hunter Colour Difference Meter. Other criteria were scored subjectively according to detailed descriptions. The criteria and weightings were stated to be "assigned according to consumer preference in the Middle East". However no support was given to this statement.
A summary of the ideal loaf according to Qarooni et al. (1987) follows: the bread is of round shape with smooth surfaces and minimal cracks; no blisters; upper crust of golden brown; complete layer separation;layers of equal thickness; soft moist crumb of creamy colour; the bread should be soft and flexible whilst offering some resistance to tearing; and should have good keeping quality. This description takes into consideration a wide range of features for both appearance and eating quality. It also allows specific faults to be identified.
Many of the features mentioned by other scoring systems, referred to earlier, were included, although the acceptance of crust blisters and the desirable crust colour is different to Faridi and Rubenthaler (1983, 1984a).
Since this system was published, a survey designed to establish preferences for Arabic bread has been completed (Qarooni 1988b). The survey covered 1400 consumers of mixed nationality in Kuwait. Results of the survey support the
24 criteria used by Qarooni et al. (1987).
Cornish and Palmer (1988) proposed a scoring system based on that of Qarooni et al. (1987). In the proposed system the same weighting was given to 10 criteria. This system has been designed for simple and rapid screening of large numbers of samples to support a wheat breeding programme. The effectiveness of this system in identifying superior quality advanced lines has yet to be established.
The scoring system of Williams et al. (1988) was designed to evaluate bread for a specified market and an effort was made to establish product requirements. The result was a system with 10 criteria, all scored out of 5. Bread diameter was the only objective measurement. Good descriptions were included for the other criteria. Many of the features are similar to thc;~described by Qarooni et al. (1987). Features which were different included the assessment of dough handling at dividing and sheeting,and taste and smell (included to identify any off flavours or smells).
Of the baking methods and scoring systems described, only those of Qarooni et al. (1987) and Williams et al. (1988) were shown to be reproducible. Both methods were also shown to offer discrimination between flour samples. These methods appear appropriate for evaluating the factors affecting Arabic bread. In both cases the nature of their subjective tests requires a trained scorer who has an appreciation of the quality criteria assessed.
25 2.4 Flour Quality
Flour quality can be an important determinant of bread quality. Variation in flour quality is due to such factors as wheat genotype, wheat growing conditions, and flour milling conditions. Many tests are used to describe the suitability of flour for the production of particular end-products. Information derived from these tests can be used by wheat breeders as selection criteria, or by wheat and flour purchasers to make commercial decisions.
a.~d ,,u.ltt~ Q..,.C For pan breads, protein content~.· the major factors to account for variation in loaf volume within wheat varieties
(Pomeranz 1987). Finney & Barmore (1948) showed this relationship to be linear, an observation subsequently confirmed (Fifield et al., 1950; Bushuk, 1985). A range of other tests are used to explain the differences in baking quality between varieties and to describe the quality of individual flour samples (Jardine et al., 1963). More recently, tests are being developed which require very small samples size and increasingly sophisticated technology. For instance HPLC is being used to identify high molecular weight glutenin subunits which have been identified to be associated with wheats suitable for pan bread production (Singh et al., 1990) •
Very little study has been completed on the relationship between flour quality and Arabic bread production. In
26 particular there is little evidence concerning the influence of wheat cultivar on Arabic bread quality.
Faridi and Rubenthaler (1983) examined six different wheat cultivars and four different wheat blends for the production of Arabic bread. These included: Hard Red Winter (HRW) , Soft
White Winter (SWW) and Club wheats. Flour milled from these samples was assessed for protein content, ash, flour colour, and was test baked as Arabic bread. The study identified wheats suitable for Arabic bread production, but did not provide a description of flour quality requirements. The two cultivars most suited to Arabic bread production were quite different to each other. Wanser was a HRW with a flour protein of 11.9% and the other was Dawes which was a sww at 9.8% protein. These results do not allow any conclusions to be drawn regarding optimal wheat or flour quality for the production of Arabic bread.
Williams et al. (1988) examined single samples of five wheat cultivars for Arabic bread quality. No data were reported on the flour properties, however it was shown that the different flours affected aspects of bread quality without significantly affecting organoleptic parameters. From this study it was concluded that flours of 'medium strength' were the most suited to Arabic bread production.
In a later report by Williams and El-Haraneub (1989), another description of wheat and flour quality suited to production of Arabic bread in Syria and Lebanon was included. This
27 consisted of: "Farinograph stability of 5-7min, mixing i,,.de>t tolerance~ of about 60-80 Brabender units (BU) and particle size index (PSI) of 18-22 appear to be optimum". They also stated that white wheats are preferred over red wheats because of the high extraction used in these countries and the desire for white bread colour. No results or references were given to support the above specifications. In the same report, flour specifications for a wheat variety regarded as having "high" baking quality were presented. These results appear to fall outside the specifications provided. Over a range of sites the PSI for this wheat ranged from 12.4 - 14.5 and Farinograph stability ranged from 2.6 - 16.6 min. However no baking data was provided with these results to determine the suitability of the flour. This left the reader uncertain as to the criteria for the assessment of flour quality for Arabic bread production.
A study of 33 flour samples representing 30 different cultivars was used to examine the relationship of 18 flour tests to Arabic bread score ((Qarooni et al., 1988). Protein content of the samples ranged from 7.6% to 15.8% and both
soft-grained and hard-grained cultivars were included. Arabic bread baking scores ranged from 45.7 to 85.5. Wheat and flour properties identified as important determinants of Arabic bread quality were: grain hardness, flour colour, protein content, starch damage and protein strength. For protein content, starch damage and protein strength the relationship to Arabic bread score was found to be quadratic. Extremes of these criteria produced inferior quality bread. Optimal
28 quality bread was produced from hard wheats of intermediate dough strength with a flour protein content of 10 - 12%.
In this study an equation for the prediction of·Arabic bread score involving four flour quality parameters was derived. This accounted for 74% of the variation which suggests that it would have limitations in predicting the quality of new populations. A trial would be necessary to test this. However the equation does highlight the potential importance of Particle Size Index, flour ash, development time and viscograph peak height as flour quality criteria.
Cornish and Palmer (1988), evaluated wheat samples from a South Australian wheat breeding programme for flour quality parameters and baking potential for Arabic bread. From this they developed a useful description of the wheat and flour quality requirements for Arabic bread. They found that hard grained wheat with good milling yield and flour colour, medium protein, high water absorption, moderate strength and good extensibility was required for optimal Arabic bread quality. This was similar, but more comprehensive than the description provided by Qarooni et_al~ (1988).
2.4.1 Milling variables
In another study by Qarooni (1988a), milling variables including the extraction rate and level of starch damage were examined. For the study of optimal extraction rate a single wheat sample was milled to extraction rates of
29 72.5,77.0,82.0,87.0 and 92.0%. The wheat sample selected had a high protein content and apart from the lowest extraction rate, all flours had a protein content higher than 12.0%, which had been defined by this study as the upper limit of flour for optimal baking quality. Optimal extraction rates were identified at 77.0% and 82.0%, with bread scores dropping off sharply above 82.0%. Because five of the six milling extractions had protein contents outside the optimum range, the conclusion drawn cannot necessarily be applied to flours within the optimum protein range.
In the same study, a commercial bakers flour with a maltose figure of 23 gKg-1 was pin milled to produce three samples with higher levels of starch damage with maltose values of 32,46 and 56 gKg-1 . Arabic bread score decreased as the level of starch damage increased. The levels of increased starch
damage are higher than those usually experienced in commercial flour milling. It would be useful to conduct a similar trial to examine starch damage over a range of maltose values from 15 to 32 gKg-1 .
. 2.4.2 Rain damaged wheat
The effects of rain damage on Arabic bread quality have been studied by Edwards et al. (1989). Using five wheat cultivars, flour from sound wheat was compared to flour derived from wheat which had been damaged using a rain simulator. For four out of five cultivars the quality of Arabic bread decreased
30 with rain damage. Bread from the rain damaged grain was of poor shape, had dark blisters and poor keeping quality. For two cultivars the bread had an unpleasant,"malty" smell and taste. The same rain damaged samples produced pan bread of higher scores than the undamaged controls. This highlights differences in the flour requirements between these breads.
Williams and El-Haramein (1989) added malt flour to sound flour to simulate the effect of rain damage. They found that at levels of 5% and higher the bread scores were significantly reduced.
The information on flour quality presented here suggests that flour quality is an important factor in determining Arabic bread quality. More work is required to determine the cultivar ''type" best suited to Arabic bread production.
2.s Shelf Life
Where Arabic bread is purchased directly from a local bakery and eaten within hours of baking, shelf life is not important. However with the advent of centralized production there is a greater need for shelf life. Automated bread plants must distribute their bread to sales outlets where the time the bread is on display will vary. In Dubai, Arabic bread may be on the supermarket shelves for up to 24 hours after baking, whilst in Australia it may be 72 hours. Shelf life of bread is limited by two considerations namely, spoilage by microorganisms and staling.
31 2.s.1 spoilage
Bread spoilage is caused by contamination with either mould or bacteria. Its occurrence will depend on bakery sanitation and storage temperature and humidity.
In a study on modified atmosphere packaging of Arabic bread, it was found that bread packaged in air was spoilt by the appearance of mould in 24 hours (Avita! and Mannheim, 1988). Bread which was packaged in 99% carbon dioxide was not spoiled by mould up to 12 days after baking.
Apart from modified atmosphere packaging, preservatives can be used to inhibit spoilage or bread can be frozen. Both freezing and modified atmosphere packaging would add significant cost to the bread.
2.s.2 staling
Staling is a process of chemical and physical changes which begins after baking. These changes to the bread result in a loss of consumer acceptance. It is therefore necessary to understand the processes taking place if they are to be stopped, slowed or reversed and to identify the consumer requirements in order to make measurements of staling relevant.
The main changes are: moisture redistribution,
32 retrogradation, increased bread firmness, crumbliness and loss of flavour.
Moisture redistribution: During baking a moisture gradient is established in the loaf. After baking, moisture moves from the centre of the loaf to the crust to equilibrate the moisture distribution. For pan bread the movement of moisture is said to make the crust tough and leathery, which is generally undesirable (Pomeranz, 1987). The same effect in
Arabic bread is probably essential for the crust to become soft and flexible. It is possible that the high crust to crumb ratio of Arabic bread may increase the significance of this redistribution, however no discussion of this was found in the literature.
Starch retrogradation: The extent of gelatinization during baking is dependent on the available moisture and the heating time at a particular temperature. Varriano-Marsten et al. (1980) found that the degree of starch gelatinization and swelling in baked products paralleled moisture content. Mahmoud and Abou-Arab (1989) found moisture contents for commercial samples of baladi and Arabic bread in Cairo of 38% and 28% respectively. Pan bread moisture is in the order of 40% (Varriano-Marsten et al., 1980). It would be anticipated that the low moisture content of Arabic bread would result in lower levels of starch gelatinization than in either baladi or pan bread. Using polarized light microscopy, Qarooni (1988a) found that for Arabic bread there was a thin layer of ungelatinized starch on the upper surface (upper crust) and
33 that the rest of the starch had gelatinized as evidenced by loss of birefringence. For pan bread the extent of gelatinization was found to range from 33% for the crust to 70% for crumb from the centre of the loaf (Varriano-Marsten et al., 1980). For baladi bread, which as mentioned has a higher water content, starch was approximately 90% gelatinized (Faridi and Rubenthaler, 1984b). Both studies used the glucoamylase method of Chaing and Johnson (1977), to measure the extent of gelatinization. Lineback and Wongsrikasem (1980) used a similar method to Varriano-Marsten et al. (1980), but found the level of gelatinization of pan bread crumb to be 96%. These measurements were made on starch washed from the bread, this does not include bread starch which is bound to protein. Lineback and Wongsrikasem (1980) measured the starch extracted to represent 50% of total starch, whilst neither Varriano-Marsten et al. (1980) nor Faridi and Rubenthaler (1984b) measured the quantity of starch extracted from their bread samples. It is possible that differences in extraction may account for differences between results. In addition, retrogradation of the starch will also influence gelatinization measurements based on enzymic methods.
After baking the gelatinized starch of bread begins to crystallize, this is known as retrogradation (Schoch, 1965). Both starch components retrograde, however amylopectin appears to contribute most to the overall starch crystallization (Lineback, 1984). Starch retrogradation is thought to contribute to crumb firming in pan bread,which is
34 the main reason for the loss of consumer acceptance (D'Appolonia and Morad, 1981). For Arabic bread the effect of staling is probably manifested as a loss of flexibility and strength, which are also features of consumer acceptance.
Moisture content: Rogers et al. (1988) found that both the rates of bread firming and starch retrogradation were affected by moisture content. Lower moisture content resulted in faster bread firming, but slower starch retrogradation. This inverse relationship is not fully explained and reflects the fact that the process of bread staling is still not fully understood.
2.5.3 Retarding staling
Baladi bread baked at higher temperatures was found to be softer initially and remained softer over 48 hours than samples baked at lower temperatures( Faridi and Rubenthaler, 1984b).This may be attributed to the higher moisture content of these samples, however no moisture results were given to confirm this. Maximising bread moisture content through production, bread cooling and storage may therefore be a means of reducing bread firming. The results of Mahmoud and Abou-Arab (1989) appear to contradict this. The rate of staling for Arabic bread was found to be slower than for baladi bread as measured by a test panel. Factors in production other than final moisture content may account for this result.
35 The rate of starch retrogradation increases as storage temperature decreases until the product is deep frozen at which point the process stops. Therefore bread should either be stored at room temperature or frozen to reduce the rate of staling (Hoseney, 1986). Starch retrogradation can be reversed by heating to 70°C, and this treatment effectively refreshens the bread (Brechtel, 1955). Arabic bread can be successfully freshened by heating (Avital and Mannhiem,
1988).
Emulsifiers and surfactants, such as trans saturated monoglycerides or sodium steroyl lactylate, act to soften bread crumb (Pomeranz, 1987). Shortening has also been found to reduce the rate of bread firming (Ghiasi, 1984). Qarooni et al. (1989b) found that SSL at 3gKg-l improved second day scores, which is an evaluation of keeping quality. A combination of SSL (2.5gKg-1 ) and shortening (5gKg-1 ) offered
the best improvement in keeping quality. These levels of additives are lower than those used for pan bread. This is because at higher additions the emulsifiers and surfactants
tend to make the bread weaker and although it is softer, it
cracks when rolled or folded (Qarooni, 1988a).
Avital and Mannheim (1988) found that packaging Arabic bread in a modified atmosphere of 99% carbon dioxide reduced the rate of staling compared to bread packed in air. The mechanism by which the carbon dioxide atmosphere slowed the rate of staling is unclear and perhaps this study should be confirmed before there is any investigation of the mechanism.
36 Different wheat samples were shown to have second day bread scores ranging from 11 to 40 (Qarooni et al., 1988). This may be due to a number of factors such as bread moisture content, cell structure of the crumb, moisture distribution or starch
gelatinization patterns. It is possible that different pentosan contents or ratios of amylose to amylopectin may affect the shelf life of Arabic bread. Differences in starch gelatinization behaviour have been recorded for Australian wheat cultivars (Moss and Miskelly, 1984). However no attempt at relating differences in starch to bread staling rates appear to have been made.
2.6 Fractionation and Reconstitution
Fractionation and reconstitution methods provide a technique to examine the role of flour components. It involves the separation of flour fractions which can then be recombined in different proportions or can be exchanged between flours.
When using this approach it is important to ensure that the
fractions are not altered by the process. This can be tested by recombining the fractions in their original ratios and
comparing flour function with the original flour.
The four basic flour components to be examined here are w,t.e,. Jo/c.e hies, ~gluten, starch and lipid.
37 2.6.l water-solubles
This fraction consists of a mixture of compounds including: albumin and globulin, soluble carbohydrates, amino acids and peptides (MacRitchie 1984). Finney (1943) found that for two out of three cultivars the water soluble fraction was required for loaf volume. Hoseney et al. (1969a) identified that the water-soluble fraction contributed to gas formation and to gluten extensibility. In the same study they found that whilst this fraction was required for a "normal" loaf of bread, it did not account for any differences in loaf volume between flours. This result was subsequently supported by MacRitchie (1978).
In a review discussing the role of flour fractions, MacRitchie (1984) states that "the water-soluble fraction may be omitted from reconstituted flours without detrimental effects on baking providing steps are t_aken to ensure that gas production is not limited". This was not supported by any data and does not appear to take into account observations made by Hoseney et al. (1969b) that reconstitution with yeast food replacing the water soluble fraction achieved a smaller volume than when this fraction was included.
There are no reports on the role of water solubles in the baking of Arabic bread.
38 2.6.2 Gluten
Using fractionation and recombination techniques, Finney
(1943), found that the gluten proteins accounted for differences in loaf volume between the cultivars studied. A similar result was found by MacRitchie (1978). Further fractionation of gluten has been based on its solubility in dilute acid solutions, however there is some disagreement in the literature about the role of gluten fractions. Hoseney et al. (1969b) found that the gliadin fraction controlled loaf volume and this was confirmed by Finney et al. (1982). MacRitchie (1978) attributed differences in loaf volume to the glutenin fraction and in particular the high molecular weight glutenin fractions. These differences in conclusions appear to be due to the different fractionation methods used. A study by Chakraborty and Khan (1988) compared gluten fractionation methods of both Hoseney et al. ( 1969b) ; MacRitchie (1978), using two wheat cultivars previously used by Hoseney et al. (1969b). They found that whilst the different fractionation methods affected the magnitude of the response, loaf volume was associated with the glutenin fraction for both methods studied.
No studies on the role of gluten or gluten fractions on Arabic bread have been reported, although the results of Qarooni et al. (1988) on the relationship between protein content and Arabic bread quality would suggest that gluten has an important role.
39 2.6.3 starch
Although essential for bread making, the starch fraction has not generally been found to account for significant differences in bread making potential between wheat varieties
(Hoseney et al., 1969b; MacRitchie, 1978). When comparing the fractionation procedures of the above workers, Chakraboty and
Khan (1988) found that using the fractionation method of
MacRitchie (1978) the starch of the cultivar Prodax increased the loaf volume of the cultivar Len. The opposite result was achieved when the method of Hoseney et al. (1969b) was used where the starch of Len increased the loaf volume of Prodax.
It was attributed to the different protein levels of the starch isolated by either method. This highlights the need to
identify the composition of fractions to allow the correct
interpretation of results.
Again, there are no reports in the literature on the role of
starch in Arabic bread other than what has been discussed in
the section on shelf life.
2.6.4 Flour lipid
Lipid function in pan bread has been investigated using
fractionation and reconstitution techniques. Flours defatted with either petroleum ether (PE) or chloroform have been
40 successfully reconstituted with their original lipid content to give pan bread of equivalent quality to the original flours (Pomeranz et al., 1968; Hoseney et al., 1969c; MacRitchie and Gras, 1973) Of these solvents chloroform was found to extract a greater quantity of lipid (MacRitchie and Gras, 1973).
Doughs prepared from flours defatted with chloroform and reconstituted with different lipid levels had equivalent loaf volumes after their final proof. However after baking their volumes were different (MacRitchie and Gras,1973). This observation can be attributed to non starch lipids which appear to stabilize the expanding cell structure during baking (Wehrli and Pomeranz, 1970).
For cookies a similar role for flour lipid has been described. When cookies were baked from flours defatted with hexane, the loss of top grain and poor internal structure were attributed to a breakdown of gas cells during oven expansion (Clements and Donelson, 1980).
Lipid composition was found to be significant for both pan bread and cookies. In pan bread, the polar lipid fraction supported loaf volume and non polar lipid depressed loaf volume ( Daftary et al., 1968; Ponte and De Stefanis, 1969; MacRitchie and Gras, 1973). For cookies, the lipid components found to restore cell structure were digalactosyldiglyceride and monogalactosyldiglyceride, which are polar lipids (Clements and Donelson, 1981).
41 A study of North American wheat and flour samples found a significant, positive correlation between free polar lipids and loaf volume (Chung et al., 1982). A similar relationship has been established for Canadian (Bekes et al., 1986) and Australian wheat cultivars (Panozzo et al., 1990). Bell et al. (1987) using wholemeal samples representing 21 wheat cultivars found no correlation between any lipid fraction and loaf volume. A study of commercially milled and laboratory milled flour samples also failed to establish a useful relationship between the polar lipid fraction and loaf volume (Larson et al., 1989). Differences in wheat samples, lipid extraction method and baking tests have led to inconsistent results between studies. Although this has made the role of flour lipid difficult to establish, it remains apparent that lipids do have a function in the baking of pan bread and that some differences in baking quality between flours may be due to their lipid content.
To date no experimental work has been published on the role of flour lipids in the baking of Arabic bread. The processing conditions, and flour quality requirements for Arabic bread appear to be different to those of pan bread (Sections 2.1.2 and 2.4). Accordingly it is possible that the role of flour lipids in Arabic bread is different to that described for pan bread and cookies.
42 2.1 conclusion
Arabic bread is a staple food of many countries of the Middle East and has become popular in many other places of the world. Information on this product is limited, less than 35 references were available in the Food Science and Technology Abstracts from 1970 to 1989. Study is needed both to confirm the results of existing publications and to explore new areas.
Information on the factors affecting Arabic bread quality will be of assistance to those marketing and purchasing wheat, wheat breeders, flour millers, and bakers.
43 3 MATERIALS AND METHODS
3.1 Amylograph Test
Brabender amylograph testing was performed according to the manufacturers instructions (Brabender, Germany). The instrument was fitted with a 250 cmg sensitivity head. The initial paste temperature was registered as the curve reached 20 Amylograph units (AU).
3.2 Bread Moisture
The fresh weight of six loaves was measured two hours after baking. As all loaves were prepared from the same dough weight, this measurement was used to provide a rapid assessment of bread moisture.
3.3 crust and Crumb Colour
Objective crust colour measurements were made with the Minolta Colour Meter according to the manufacturers instructions (Minolta, Osaka, Japan).
3.4 Determination of Ash Ash content of flour was determined according to AACC method 08-01.
44 3.5 Determination of Flour Colour Grade
Flour colour grade was estimated according to Kent-Jones and Amos (1967).
3.6 Determination of Falling Number
Falling number for flour was determined according to ICC
Standard method 107, using the Falling Number 1600 apparatus
(Falling Number, Sweeden).
3.7 Determination of Flour Moisture
Flour moisture was determined according to AACC method 44-
15A.
3.8 Determination of Maltose Figure
Diastatic activity (maltose figure) was determined according to AACC method 22-15.
3.9 Determination of Particle Size Index (PSI)
Particle size index was estimated according to the method of
Symes (1961).
45 3.10 Determination of Protein Content
The protein content of samples was determined by Kjeldahl using the Tecator 1030, according to the manufacturers instructions (Tecator, Sweden). This is in accordance with AACC method 46-12. The sample size used for each type of sample follow: wheatmeal lg, flour lg, starch 1.5g, gluten O.lg and water-solubles 0.2g. Flour protein content has been expressed on a N x 5.7, 13.5% moisture basis (mb).
3.11 Determination of Damaged Starch
Starch damage was determined according to AACC method 76-30A.
3.12 Flour Samples
3.12.1 Flour samples for sections 4.2 and 4.3
Commercial flour samples were obtained from Weston Milling (N
B Loves Industries Pty Ltd), Sydney.
3.12.2 Flour samples for section 4.4
A commercial bakers flour similar to that described for section 4.3 was used for the preparation of all bread samples for this section.
46 3.12.3 Flour samples for section 4.5
Wheat samples described in section 3.24.1, were milled to an extraction of 80% on a Buhler test mill (Section 3.21).
3.12.4 Flour samples for section 4.6
Flour was milled from the wheat samples described in section 3.24.2. The commercial wheat sample was milled by a local flour mill to produce a white bakers flour. The cultivar Hartog was milled to an extraction of 78% on the Pilot Mill at the Bread Research Institute of Australia. This mill has the capacity of 750 Kg hr-1 and produces flour of commercial quality (Moss, unpublished). The wheat samples of the cultivar Halberd were milled individually on a Buhler Laboratory Mill to an extraction of approximately 74%, these flours were then mixed to give a single sample.
3.13 Fractionation and Reconstitution of Lipid
3.13.1 Defatting of flour samples
Flour samples were defatted and stored according to the procedure of MacRitchie and Gras, (1973) with the following modifications: (1) a glass rod was used to stir the chloroform/flour slurry for one minute rather than an electric stirrer for three minutes; (2) the filtrate was evaporated at 30°C rather than 40°C and (3) each batch extraction was for 450g of flour with three solvent washes
47 each using 900ml of chloroform. The flour and lipid batches were mixed to provide the required quantities for baking tests. Lipid was quantified by acid hydrolysis according to
AOAC method 922.06.
After defatting flours were sieved using a coarse sieve (0.5mm) and then equilibrated to a moisture content of approximately 13.5% in a cabinet at 30°C and 65% RH for 24 to 48 hours.
3.13.2 Reconstition of defatted flour samples
For reconstitution of lipid to defatted flour, flour was spread in a flat tray and the lipid added as droplets to the surface of the flour using a Pasteur pipette. The lipid droplets were covered with some of the flour sample before adding the sample to the farinograph bowl.
3.13.3 Separation of polar and nonpolar lipid
Flour lipid was separated into polar and nonpolar components by the method of Ponte and De Stefanis (1969), except that a total of 10 elutions of the silica gel rather than 4 were completed with each of the polar and nonpolar solvents.
3.13.4 Reconstitution of lipid fractions
The fractions were added back individually and baked. The polar lipid was added at a level of 35% and nonpolar lipid
48 was added at a level of 65% of the total lipid extracted. These levels were based on the ratio of the lipid fractions established by Ponte and De Stefanis (1969). The polar lipids were too viscous to add by Pasteur pipette and a spatula was used. Non polar lipids were added with a Pasteur pipette as for the whole lipid.
3.14 Measurement of Starch Gelatinization Using Glucoamylase once loaves were cool, a 25g sample with equal proportions of both the upper and lower layers of a loaf was weighed. Starch was then extracted from the sample according to Varriano Marst$1 et al., (1980) and freeze dried. A 20mg sample of this was then used to determine the degree of starch gelatinization by the glucoamylase method described by Chiang and Johnson (1972). The glucoamylase used was obtained from Sigma Chemical Co., U.S.A., catalog N, A-7255. A sample of pregelatinized starch was used as reference.
3.15 Microscopy
3.15.1 Light microscopy:
Sections (5mm2 ) were cut from three points in the upper and
lower layers of the loaf, which were half way between the outside edge and the centre of the loaf. These crust samples were placed in a Tissue-Tek O.T.C. solution 50 % Tissue-Tek O.T.C., Miles Scientific, U.S.A., and 50% water,
49 the pressure of the system was reduced to remove air bubbles before sectioning (Moss, 1975). The 103mm sections were stained with Ponceau 2R (C.I. No.16150) and viewed under polarised light. Two sections were examined from three sept..rate bakings for each treatment.
3.15.2 Electron microscopy:
Specimens (8 x 3mm) were cut from the upper crust, half way between the edge and at the centre of the loaf. The specimen was first fixed to an aluminium stub with colliodal carbon before being frozen in a liquid nitrogen slush. It was transferred to a Poloron E7400 Cryotrans system held at -165±5°C where it was fractured with a cold knife. The specimen was transferred to a stage in the electron microscope (Cambridge Stereoscan 360, Cambridge Instruments, United Kingdom), and held at -80±l°C and a pressure of 2.6 x 10-5 torr, for ten minutes to etch the surface. The specimen was then coated in the Cryotrans system by spluttering with gold/paladium to a thickness of 200 angstrom. The specimen was then returned to the microscope and held at -170°C during microscopy.
3.16 Mixograph
Mixograph mixing times were obtained following AACC method 54-40. For a 10g Mixograph (National Manufacturing Division TMCO, Nebraska, USA), 6.0mL of a 3.5% salt solution was used for all mixographs.
50 3.17 Physical Dough Testing
3.17.1 Farinograph
Flour water absorption and dough resistance to mixing were measured using AACC method 54-21. A Brabender Farinograph, (Brabender, Germany) fitted with a 50g bowl was used for testing. 50g of flour was used without adjustment for flour moisture content.
3.17.2 Extensograph
Extensograph tests and interpretations were made in accordance with AACC method 54-10.
3.18 Test Baking
3.18.1 Test baking of Arabic bread
Two test baking methods were used: 1) The method of Qarooni et al (1987) was used in Sections 4.1 and 4.2.2. This method is described in more detail
including des~1pt1ons~ . of the equipment in Qarooni et al. (1987).
2) An alternative test baking method was developed (Section 4.2.) using the same equipment, and the same procedure as for Qarooni et al. (1987) and Qarooni (1988a), except for the following changes:
51 a) Final roll gap of the sheeting rolls was set to a gap of 1.1mm, rather than the gap of 1.5mm used by Qarooni et al.
(1988).
b) Baking temperature and time were 550°C for 33sec rather
than 400°C for 90sec.
3.18.2 Scoring of Arabic bread
Two scoring systems for Arabic bread were used in this study:
1) The scoring system of Qarooni et al. (1987) was used in section 4.2.
2) A second scoring system was developed (Section 4.2) and
this system was used for all bread scoring unless specified. A description of this system is presented in full below. A
comparison between this system and that of Qarooni et al.
(1987) is made in section 4.2.
A list of the bread characteristics assessed is presented in
Table 3.1. A trained operator scored four loaves two hours
after baking (first day), and two loaves 24 hours after
baking (second day).
52 Table 3.1 Arabic bread scoring system
Character Score Character Score
First Day: Area 5 Crumb texture 5 Shape 5 Crumb appearance 5 Smoothness/cracks 5 Evenness of layers 5 Crust colour 5 Tearing 10 Blisters 5 Day: Two Rolling and folding 10 Rolling and folding 20 Pocketing 10 Tearing 10
Total 100
These parameters were scored according to the description of the quality features presented below.
,.,,,e,. Suf'Jq,e,e Area: Thelarea of two loaves was measured in cm2 and this was added together. This is based on the premise that consumers prefer larger loaves. This score can be adapted for
commercial bakeries where each loaf must be the required
size to meet specific packaging requirements.
Shape: A round shape is desirable, with points being deducted
for lack of symmetry.
Smoothness/cracks: Ideally the surfaces of the upper and
lower crusts should be smooth. No cracks should appear on
the upper surface and large cracks on the bottom layer are not desirable.
53 crust colour: An even, golden brown colour is the most desirable. This is referenced to the Minolta Colour Meter where optimum colour range is defined as being between x=0.360 to 0.374.
Blisters: An ideal bread should be free of blisters.
Ability to Roll and fold: The loaf should be soft and flexible. Breads which crack when either rolled or folded are not acceptable. Application of this criterion 24 hours after baking was used as a measure of staling.
Pocketing: Apart from the outer edge, the top and bottom layers should be completely separated. These layers should remain easy to separate when the loaf has cooled. The layers should be of equal thickness.
Bread crumb: The crumb should be a creamy white colour (unless baking wholemeal bread), with a fine uniform cell structure and a soft moist texture.
Tearing quality: When the bread is torn it should offer some resistance without appearing too strong. This assessment was related to the mouthfeel of the bread which should be chewy without being tough.
Although bread flavour and aroma have not been included in the scoring system, these features were evaluated when
54 samples were assessed. Comment would be made when an unusual flavour or aroma was observed for a specific sample.
Breads are considered to be of acceptable quality if they have a score greater than seventy, and have no adverse comments concerning aroma and flavour. Breads with a score greater than seventy five (and no adverse comments), are considered to be of good quality.
3.18.3 Test baking for pan bread
Pan Bread: Pan bread was baked and scored by the conventional method described by Moss (1980). The mixing time
and water addition were optimised according to the ,. ~-- r 1 n:ograph mixing curves. Samples were baked with both 10 and 20ppm added bromate.
3.19 Fractionation and Reconstitution of starch, Gluten and
Water-Solubles
3.19.1 Fractionation of starch, gluten and water-solubles
A 400g flour sample was mixed with 240mL of deionized water in a Hobart mixer (Crompton Parkinson, Australia) until a
coherent mass was formed. This was then hand kneaded in 6 changes of water. The temperature of all washing water was maintained at 15°c in accordance with MacRitchie (1978). The first two washes were in 800 mL each, the next two were in
55 400 mL each, and the third two were in 200 mL each. After each washing the liquid was poured through a sieve (0.5mm). On completion of the washing the insoluble material or gluten, was rested for 30 min before being frozen. The combined washing liquid was then centrifuged at 5000 G for 10 min. The sediment (starch) and supernatant (water solubles) were separated and frozen. Gluten, starch and water-solubles were then freeze dried.
Dried starch and water-solubles were ground in a coffee grinder and sieved (0.5 mm). The gluten was ground in a KT grinder (Falling Number, Sweden). The samples were then weighed and stored in sealed containers at 15°C.
3.19.2 Reconstitution of starch, gluten and water-solubles
Using the moisture and protein data the calculated proportions of ingredients were mixed by spatula and then allowed to equilibrate in a cabinet maintained at 65% RH and 30°C for 24 to 48 hours. They were then mixed for one min in the Farinograph bowl before water addition. Correct water addition for samples was estimated using a 50g Farinograph bowl.
3.20 Statistical Analysis
Statistical analyses were performed using the statistical
program GENSTAT (Alvey, 1980).
56 3.21 Test Milling
Wheat samples for section 4.4 were milled on a Buhler laboratory mill, model ML202 (Buhler, Switzerland), to 80% extraction. To attain the desired extraction rate, the bran and the pollard were passed three times through a Buhler laboratory bran finisher and the throughs (<130 um) were blended with the flour. All flour samples were stored in sealed containers at 12·c until studied.
3.22 Thin Layer Chromatography
Thin layer chromatography (TLC), was performed according to the method of MacRitchie (1977).
3.23 varietal Identification
For confirmation of variety, samples were checked against a library of known varieties using a modification (Gore unpublished) of Bietz et al. (1984).
3.24 Water Activity
A Sina Water Activity Meter (Novasina, Pfaffihon, Switzerland) was used in accordance with the manufacturers instructions.
57 3.25 Wheat samples
3.25.1 Wheat samples for section 4.5
Forty-nine samples of wheat representing nine cultivars with a range of protein contents were obtained from the Australian
Interstate Wheat Variety Trials (AIWVT) for the 1986/87 and
1987/88 seasons. These field trials are grown at a number of sites in the five mainland states of Australia, and thus allow a comparison of varieties grown under a range of soil and climatic conditions.
3.25.2 Wheat samples for section 4.6
The sample of the cultivar Hartog was grown in the 1988/89 season in New South Wales. The sample of the cultivar
Halberd was obtained from various sites throughout Australia by the AIWVT. A third sample was a commercial blend of Hard grained Australian cultivars.
58 4 RESULTS AND DISCUSSION
4.1 Importance of Arabic Bread to Australia
Australia is a major exporter of wheat to the Middle East. Much of this wheat is used to produce Arabic bread, one of the most common breads of the region. Arabic bread is also popular in many other countries including Australia. In this section the importance of this product to Australia is established on an economic basis.
4.1.1 Australian wheat exports to the Middle East
Australia exported 5.8 million tonnes of wheat to the Middle East region from the 1988/89 harvest, this represented 51% of
total Australian wheat exports (Australian Wheat Board,
1989). Of this, 2.8 million tonnes went to countries where Arabic bread is a major product. Average annual export to these countries from 1986 to 1989 were: Bahrain 20,735, Egypt 1,980,353, Kuwait 57,368, Oman 115,409, PDR Yemen 152,029, Qatar 33,047, United Arab Emirates 174,945, Yemen AR 336,879 tonnws (Australian Wheat Board, 1989). Iran and Iraq are examples of major markets that produce breads other than Arabic bread for major consumption and for this reason they
were not included.
59 Based on average wheat prices from the 1986/87 to 1988/89 harvests, annual earnings from wheat exported to countries producing Arabic bread as a major end use approximated A $555,550,000 (Australian Wheat Board, 1989).
4.1.2 Australian consumption of Arabic bread
Arabic bread was introduced into Australia by migra··:~,+-;.: from the Middle East, in particular the Lebanese. Initially Arabic bread was manufactured in small local bakeries which catered for the ethnic communities. With the growing size of these communities and a greater acceptance of ethnic food in Australia, there was an increase in the availability of Arabic bread. To assess the consumption of Arabic bread in Australia, a survey was made of the domestic flour milling industry. All known flour mills in Australia were sent a questionaire. This covered 8 companies representing 40 mills. The questionnaire (Appendix 1), was sent to the mills in July 1989. The aim was to identify the quantity of flour supplied for the production of Arabic bread over a period of four years and to determine the number of bakeries.
Results from the survey can only be discussed in very general terms as the information supplied by the flour mills is considered confidential. Five mills did not respond, however it was considered from their location that it is unlikely that they would supply flour to Arabic bread bakeries. Flour statistics presented in Table 4.1 include the results of this survey, and for comparison, results from the Bread Research
60 Institute of Australia's National Flour Survey. These results indicate that the consumption of Arabic bread has increased over the past 5 years. This is consistent with the appearance of a range of products on Supermarket shelves. The product is now available in all capital cities in Australia and is manufactured in all states. The survey response to the provision of names and locations of bakeries was poor.
Apparently the mills considered this information too confidential to disclose. Approximate numbers of bakeries in each state in March 1990 were: Sydney 22, Melbourne 9, Queensland 3, Western Australia 3, South Australia 1 and Tasmania 1. This information was obtained from listings in telephone directories and was supported by discussions with operators of bakeries in each state.
Table 4.1 Flour sales of Australian flour mills for Arabic bread and total bread production.
Year 1986 1987 1988 1989 Tonnes Tonnes Tonnes Tonnes
Arabic bread 2,313 4,259 4,479 5,595 Total bread 523,096 540,914 562,705 595,650
The concentration of bakeries in Sydney and Melbourne is due to both their larger populations and their higher number of migrants from the Middle East. No prediction of future consumption trends could be made on the information available.
61 An approximate price for flour in Australia in 1989 was A$410 (G. Wise, Pers. Comm.). This meant that in 1989 approximately A$2,294,000 of flour was sold for the production of Arabic bread.
4.1.3 conclusion
The value of Australian wheat exports to countries in the Middle East which produce Arabic bread and the value of domestic flour sales for this product are economically significant. Therefore information on the factors affecting Arabic bread quality is of value to Australia's economy through support of both wheat export and domestic bread markets.
4.2 scoring system for Arabic Bread
Of the scoring systems discussed (Section 2.3), that of Qarooni et al. (1987) appeared to be the most thorough and was supported by a survey of consumers in the Middle East (Qarooni, 1988b). However this scoring system was considered too complicated and therefore a new scoring system was developed.
62 The scoring system of Qarooni et al. (1987) applies seven different maximum scores so that for each parameter assessed the operator must convert the assessment to an appropriate score. For instance a rating of "satisfactory" for different parameters can translate into scores of 3.8, 5.2, 6.0, 7.5, 12.0, 15.0 or 22.5 depending on the maximum score allocation for that parameter. The need to think about the score allocation distracts from the actual process of bread evaluation. For this study the scoring system of Qarooni et al (1987) has been modified so that all the maximum scores are a multiple of five. Therefore a score of satisfactory would be scored as either 3,6 or 12 depending on the parameter. Other changes were made that simplify assessment yet still maintain the emphasis of weighting proposed by Qarooni et al. (1987). These are presented in table 4.2.
Although bread flavour and aroma have not been included in the scoring system, these features were evaluated when samples were assessed. Comment would be made when an unusual flavour or aroma was observed for a specific sample.
Breads are considered to be of acceptable quality if they have a score greater than seventy, and have no adverse comments concerning aroma and flavour. Breads with a score greater than seventy five (and no adverse comments), are considered to be of good quality.
For a full description of the proposed scoring system see section 3.18.2.
63 Table 4.2 Comparison between scoring systems of Qarooni tl .2.l (1987) and present study
Qarooni et fil (1987) Present Study Explanation Maximun Character Maximum Character ---Score Score [* as for Qarooni et fil (1987)]
EXTERNALFEATURES (FIRST DAY)
Area 5 Area 5 The area of two full sized loaves was measured and added together (cm2 ). This area takes into account the effect of sheeting and shrinkage or expansion after sheeting. This is based on the assumption that for a given dough weight consumer preference is for a larger loaf. Qarooni tl fil (1987) cut loaves to a standard area after sheeting, this leaves out the effect of sheeting which is the most important determinant of final loaf area. Shape 7 Shape 5 * Crust Smoothness 5 Smoothness and cracks 5 The crust's smoothness and cracks are combined as a single assessment rather than being scored separately. Cracks 7 Crust colour 8 Crust colour 5 This was judged subjectively (optimun colour was equivalent to x=0.360 to 0.374 on the Minolta colour meter, (Appendix 2) rather than measurements on smaller cut pieces using the Hunter Laboratory yellow index. Blisters 8 Blisters 5 * Ability to roll and fold 10 Ability to roll and fold 10 *
INTERNALFEATURES (FIRST DAY)
Quality of separation 16 Quality of separation 10 * Crunb texture 7 Crunb texture 5 * Evenness of layers 5 Evenness of layers 5 * Grain appearance 5 Crl.llb appearance 5 This visual assessment of the crl.llb takes into account the appearance, colour and uniformity of the crl.llb features Crunb colour 5 as described by Qarooni tl fil (1987). Grain uniformity 5 Quality of tearing 7 Quality of tearing 10 *
SECONDDAY
Ability to roll and fold 30 Ability to roll and fold 20 * Quality of tearing ..1Q Quality of tearing .J.Q *
TOTALSCORE 150 100 A trial was conducted to compare the scoring systems. This was done to determine if the changes made to the scoring system of Qarooni et al. (1987) would significantly affect the evaluation of bread quality. Flour samples A,B and c (Table 4.3) were test baked in triplicate and scored according to Qarooni et al. (1987). Breads were also scored using the system proposed by this study.
Table 4.3 Flour sample data
Flour Sample Parameter Commercial A B C Bakers
Protein (%) 11.1 11.1 9.2 13.4 Maltose (gKg-1) 18 16 11 15 Farinograph 65.5 64.4 58.8 65.2 Water absorption (%) Development time 5.0 4.2 3.0 6.5 (min) Extensograph 233 221 205 265 Extensibility (mm) Maximum Height 350 330 410 430 (EU)
The results (Table 4.4), showed that there was a significant difference between scoring systems and between samples (P < 0.01). However there was no significant interaction between scoring systems and samples. Scoring by both systems ranked samples in the same order and expressed very similar differences with samples A and B scoring similarly and sample
c scoring significantly lower (P < 0.01) than either samples
A and B. The scoring system of Qarooni et al.(1987)
65 resulted in higher scores. Low statistical interaction between scoring system and sample suggested that the systems measured similar parameters and therefore provided a comparable assessment of bread quality.
TABLE 4.4 Comparison of scoring systems using three flour samples
Flour Samplea
Sample System A B C
Qarooni et al. 78.8 77.8 71.7 (1987) Present Study 70.8 70.7 64.5
LSD (0.05 = 3.42) ; (0.01 = 5.84)
a See Table 4.3
4.3 Effect of Baking Temperature/Time conditions and
Dough Thickness on Arabic Bread Quality and Test Baking
Method.
In commercial production of Arabic bread, processing conditions may vary between bakeries. These include dough thickness which is largely selected for consumer preference
and the baking temperature/time regime, which is often based
on technical constraints. Whilst Qarooni et al (1987) examined the effect of dough thickness over a range of 2.0-
66 6.0mm, baking temperature/time variations were not examined. The baking conditions selected by Qarooni et al. (1987) of 400°C for 90sec were said to be "the most widely used in commercial practice", however no evidence was given to support this statement. Faridi and Rub&,nthaler (1984a) reported that where bread was baked at 260°C for 4 to 6 mins and 480°C for 90 sec, the breads baked at the higher temperature for a shorter time were of superior quality. This range was very wide and the temperature of 260°c considered to be very low. Observation of Arabic bread bakeries in both the Middle East and Australia by the author, has found that baking conditions in industry range from 350°C for 120 sec to 650°C for 15 sec. There was little uniformity between bakeries, but most used temperatures higher than 450°C.
This section examines the effect of dough thickness and its interaction with baking temperature/time conditions on Arabic bread quality. Results of bread scores are supported by measurement of bread moisture and water activity.
The application of the work on dough thickness and baking temperature to test baking methodology is examined and the implication of this information to commercial production discussed.
Details of flour samples used for this section are presented in Table 4.3. Unless specified the commercial bakers sample was used for trials. All trials were repeated three times
67 and the results analysed by analysis of variance. Least significant differences (LSD) for the interactive terms were calculated for each analysis.
4.3.1 Effect of dough thickness and baking temperature/time conditions on bread quality
control of Dough Thickness
Final dough thickness was controlled by adjusting the gap between the final sheeting rolls. Four final roll gap settings were trialled and the corresponding dough thicknesses measured immediately after sheeeting. Final roll gap settings of 1.5, 1.2, 1.1 and 1.0mm produced doughs of
3.3 ± 0.2, 2.9 ± 0.2, 2.5 ± 0.2, 2.2 ± 0.2mm respectively.
Baking conditions
Each dough thickness was baked under the following temperature/time conditions: 400°C for 90 sec, 500°C for 43 sec, 550°C for 30 sec, and 600°C for 21 sec. Baking time for each temperature was determined by the time taken to develop a golden brown crust colour. Whilst this judgment is subjective, it forms the basis for determining baking time in commercial practice.
Bread Moisture (Table 4.SA)
Fresh weight of loaves was used as an index of bread
68 moisture.
Dough Thickness: The fresh weight of loaves significantly decreased (P<0.01) with decreasing dough thickness. This effect was noted at all baking temperatures.
Baking Temperature/Time conditions: An increase in bread moisture (P<0.01) was recorded as baking temperature was increased. This effect was evident at all dough thicknesses. Formation of the crust creates a barrier to the steam generated within the crumb during baking. The higher the baking temperature the faster the crust was formed and, therefore, the greater was the amount of moisture trapped in the crumb. S1. • .-ter- hc..1c ..,l t '--• • a..-t h•~hc,.. te.- ,~,..._t:"'.cc.s 4/.ro e&J-tec. ..:C ;}1""'od ""'o,1,~14.Re c..o,. 'C.e"""t..
Interaction: The combined effect of baking temperature and dough thickness resulted in large differences in bread moisture. The largest range was between the 1.0mm doughs baked at 400°C with a fresh weight of 275.2g to the highest of 315.2g for the 1.5mm doughs baked at 600°C. This represented a difference of approximately 9% moisture between these samples.
Water activity (Table 4.SB)
Dough Thickness: Water activity followed the same trend as for bread moisture where the thicker breads had higher water activities.
69 Table 4.5 Effect of combined treatments of roll gap (dough thickness) and baking temperature/time conditions on mean scores of Arabic bread quality and fresh weight.
Roll Gap (mm) 1.0 1.1 1.2 1.5
Parameter Temperature (°C)/ Time (sec) 400/90 275.2 281. 3 288.4 301.2 A.Bread 500/43 284.1 290.7 296.3 307.0 Fresh Weight 550/30 290.9 295.8 301.1 311.2 (g) 600/21 293.7 301.0 305.5 315.7 LSD: (0.05 = 4.6) (0.01 = 8.4)
400/90 0.875 0.888 0.923 0.943 B.Water 500/43 0.89 0.919 0.934 0.945 Activity 550/30 0. 912 0.924 0.938 0.949 600/21 0.916 0.932 0.943 0.96 LSD: (0.05 = 0.026) (0.01 = 0.047)
400/90 23.9 25.0 26.0 26.0 C.External 500/43 25.8 27.0 27.3 26.6 Score 550/30 27.3 27.9 28.4 27.5 600/21 28.3 29.0 28.9 27.5
LSD: (0.05 = 1.6) (0.01 = 2.9)
400/90 22.4 25.1 25.2 26.7 D.Internal 500/43 25.4 27.1 27.9 25.4 Score 550/30 28.0 29.2 27.9 26.3 600/21 29.0 29.5 28.0 25.8 LSD (0.05 1.7) (0.01 = 3.1)
400/90 14.0 17.7 20.2 16.7 E.Second 500/43 20.9 21. 7 21. 3 17.2 Day 550/30 23.3 23.7 21. 3 16.2 Score 600/21 24.2 23.2 21. 3 16.7
LSD : ( 0 . 0 5 = 2 . 1) (0.01 = 4.1)
400/90 60.4 67.7 71.4 69.4 F.Total 500/43 71.8 75.7 76.2 71.5 Score 550/30 78.6 80.7 77. 7 69.9 600/21 81.5 81. 6 78.1 70.0 LSD: (0.05 = 4.0) (0.01 = 7.4)
Note: Maximum potential scores: External (35), Internal (35), Second Day (30), Total (100).
70 Baking Temperature/Time conditions: water activity (Aw) showed similar trends to bread moisture with the 1.0mm doughs baked at 400°C having the lowest Aw (0.875) and the 1.5mm dough baked at 600°C having the highest (0.960). Measurement of Aw by Avital and Mannheim (1988) found values of 0.92 to 0.95 for commercially baked samples.
Interaction: All breads tested would be susceptible to spoilage by common bread moulds due to the high Aws. Thinner breads however might be expected to be less susceptible than thicker breads, especially when thicker doughs were baked at higher temperatures.
External Score (Table 4.SC)
Dough Thickness: External scores were not affected by dough thickness except at 400° (P<0.05). Loaf area is a component
of external score. It was found that sheeting doughs of the
same weight with different roll gaps produced dough pieces
of different thicknesses and surface areas. As the roll gap was reduced stepwise from 1.5mm to 1.0mm bread area increased
significantly (P<0.01) irrespective of baking temperature.
Thicker doughs tended to result in lighter and thinner loaves
with a darker crust colour. This would appear to be due to
differences in heat transfer resulting from the difference in
dough thickness.
Baking Temperature/Time Conditions: For 1.0mm and 1.1mm doughs there were significant increases in the external score
71 from 400°C to 500°C (P<0.01) and from 500°C to 550°C and 550°C to 600°C (P<0.05). Thicker doughs showed increases in score with increasing temperature, although differences for 1.5mm doughs were just below those needed for significance (P<0.05). This effect was most apparent for the 1.0mm and 1.1mm doughs which, when baked at 400°C, produced breads which were dry and brittle with mean scores for rolling and folding of 5.0 and 5.5 respectively. Baked at 550°C and 600°C, these breads were soft and flexible, scoring 8.6 and 8.9 respectively. Breads baked from the 1.2 and 1.5mm doughs also improved rolling and folding characteristics with increasing temperature. For the 1.2mm doughs, scores for rolling and folding improved from 6.7 to 9.0 and for the 1.5mm doughs, scores improved from 7.3 to 8.9.
Interaction: Larger surface areas of the loaves could explain the differences in bread moisture due to dough thickness.
Improved rolling and folding with increased baking temperature largely reflected the increased moisture content of these breads. For the 1.5mm doughs, with initially higher bread moistures, this improvement was not as great as for the 1.0mm and 1.1mm doughs.
Internal Score (Table 4.SD)
Dough Thickness: At 400°C the internal scores of doughs sheeted to 1.0mm were significantly less(P<0.05) than for other dough thicknesses. There was an optimum range (l.1- 1.2mm) of dough thickness at 500°C. Only 1.5mm doughs scored
72 significantly less (P<0.05) at 550°C and 600°C. Evenness of layers was a factor of internal score which improved as doughs were sheeted more thinly, from a score of 3.0 for 1.5mm doughs to 4.5 for 1.0 mm doughs.
Baking Temperature/Time Conditions: 1.0mm and 1.1mm doughs baked at 600°C and 550°C had higher internal scores than those baked at either 400°C or 500°C (P<0.05). Only 1.2mm doughs baked at 400°C (P<0.01) had a significantly lower score (P<0.05), whilst there was no effect of temperature on scores of 1.5mm doughs.
Interaction: On baking, all breads pocketed irrespective of either dough thickness or baking temperature. At each baking temperature, pocketing occurred after approximately one third of the baking time so that at 400°C pocketing occurred at 30 sec; 500°C at 21 sec; 550°C, 10 sec and at 600°C, 7 sec.
After baking at 400°C the 1.0mm doughs had a dry crumb texture (score 1.1) and were tough to tear (score 4.3). These features improved with both increased dough thickness and baking temperature such that at 600°C the crumb texture (score 4.0) and tearing quality (score 8.0) of the 1.0mm doughs were excellent. For breads produced from 1.5mm doughs when baked at 600°C the crumb was too moist and considered sticky (texture score 2.3). These differences appear to be related to the differences observed in bread moisture.
73 second Day Score (Table 4.SE)
Dough Thickness: Bread baked from the 1.5mm doughs gave significantly lower scores (P<0.05) than the other three dough thicknesses. The bread cracked on folding and lost resistance to tearing. This appears to be a result of a loss of elasticity in the bread crumb as a result of staling. Dough sheeted to 1.0mm and baked at 400°C gained the lowest score (P<0.05). However, at 550°C and 600°C the thinner 1.0mm and 1.1mm doughs yielded the highest second day scores.
Baking Temperature/Time Conditions: For 1.0mm doughs there were significant increases in scores from 400°C to 500°C (P<0.01) and from 500°C to 550°C (P<0.05), but no difference between baking at 550°C and 600°C. A significant increase in second day scores was observed for the 1.1mm doughs only between 400°C to 500°C (P<0.05). There was no significant effect of baking temperature on scores of the thicker doughs.
Interaction: When baked at 400°C, 1.0mm doughs were dry, harsh and tough. However, 550°C and 600°C treatments yielded breads which gave good scores, rolling and folding without cracking and tearing well. For these breads staling was not so rapid.This might be due to any of the following factors; fine cell structure of the crumb, moisture distribution, or rate of chemical change to starch. Causes of the differences in second day scores observed have not yet been identified. Breads baked from 1.5mm doughs were
74 inferior at all temperatures, they cracked on rolling and folding and offered little resistance to tearing. Keeping quality of thinner doughs baked at higher temperatures was superior.
Total score (Table 4.SF)
Dough Thickness: When baked at 400°C the thinnest dough (1.0mm), gave a significantly lower overall score than the other dough thicknesses (P<0.05). Optimum dough thickness at this temperature was 1.2mm. At 500°C 1.0mm and 1.5mm doughs were rated as significantly worse than the 1.1mm and 1.2mm doughs (P<0.05). At higher baking temperatures of 550°C and 600°C 1.5mm doughs were rated significantly lower (P<0.01) than the thinner dough pieces. Thin doughs (1.0mm and 1.1mm) produced the optimum scores at these temperatures.
Baking Temperature/Time conditions: For the 1.0mm and 1.1mm doughs there were significant increases in scores from 400°C
to 500°C (P<0.01) and from soo 0 c to 550°C (P<0.05). Significant improvement was noted for 1.2mm doughs only with change of baking temperature from 400°C to 500°C (P<0.05). There was no significant effect on quality of baking temperature for the 1.5mm doughs.
Interaction: When baked at 400°C, 1.0mm doughs gave unacceptable loaves. The large surface area of these breads resulted in extreme dryness at this temperature. Excellent bread was produced from these dough thicknesses at 600°C.
75 This effect appeared to be closely related to bread moisture, but it should be noted that the bread with the highest score of 81.6 for 1.1mm doughs baked at 600°C had equivalent bread moisture to 1.5mm doughs baked at 400°C with a score of only
69.4. Clearly, bread moisture was not the only factor contributing to the differences in quality observed.
Breads made from 1.5mm doughs were the only breads not to
improve with baking temperature. The most obvious difference was the poor keeping quality of these breads. For each temperature there was an effect of dough thickness. At 400°C the 1.0mm doughs gave the lowest scores of 60.4 and the 1.2mm the highest of 71.4. However at 600°C the 1.1mm doughs gave the highest scores of 81.6 and the 1.5mm the lowest score of
70.0.
consequences for Test Baking Method
~C.VC'S This study aims to define a modified method which ) optim · ;1.,. 4' ;j ,..,.,. /-lot.er ~o Q//ow ce-r-,., SO"-' product quality) within the constraints of commercial practice. Evaluation of breads baked with differing dough
thicknesses and baking temperatures has shown that superior
quality bread is produced from thinner doughs baked at higher
temperatures. A modified method is proposed which
incorporates these advantages.
4.3.2 Comparison of test baking methods
The method proposed is based on, but modified from, that of
76 Qarooni et al (1987). Dough thickness has been reduced from a final roll gap setting of 1.5mm to 1.1mm and a baking regime of 400°C for 90sec altered to 550 °C for 33 sec.
Comparison of the modifed method with that of Qarooni et al (1987) was undertaken on a set of 3 flour samples (Table 4.3): of high (13.4%), medium (11.1%) and low (9.2%) protein contents.
Bread Moisture (Table 4.6A)
Method: There was no significant effect of the methods on bread moisture.
Sample: Sample Chad significantly higher (P<0.01) bread moisture than either samples A or B which were not significantly different as assessed by either method. The higher bread moisture of sample C was a result of a smaller surface area due to shrinkage of the dough which occurred during and after sheeting. This was attributed to the high protein content of this sample.
Interaction: It has been generally assumed that thinner doughs with greater surface areas lose more moisture during baking. However, as already shown, increased baking :fo ... $ho,- G c ... tc..,., e temperature A increases moisture retention of bread. Accordingly, it was concluded that in all three flour samples baked, the effect of increased surface area was
77 counterbalanced by increased baking temperature.
External score (Table 4.6B)
Method: External scores were significantly increased (P<0.05) by the method proposed in this study for samples A and B. There was no difference in scores between the methods for sample c.
Sample: Sample A scored significantly higher than sample B (P<0.05) using the method of Qarooni et al. (1987), but there was no difference between samples A and C or Band C. With the proposed modification sample A scored the highest with good external characteristics. Sample B had pale crust colour (score 2.8) and its rolling and folding was poor (score 6.0). Sample c had the lowest score, being significantly less (P<0.05) than sample A, the bread had a small area, a rough crust surface and blisters.
Interaction: The increased external scores of samples A and B with the modified baking method were largely due to an improved ability to roll and fold of these samples.
78 Table 4.6 Comparison of two test baking methods on three flour samples using mean results for bread scores and fresh weight.
Flour Sample **
A B C
Parameter Method*
A. Fresh 1 292.5 290.8 300.7 Weight(g) 2 291.8 291.4 301. 6 LSD: (0.05 = 3.8) ; (0.01 = 7.0)
B. External 1 25.8 23.6 24.5 Score 2 28.5 26.4 24.3
LSD: (0.05 = 1.9) ; (0.01 = 3.3) c. Internal 1 26.9 24.8 23.0 Score 2 28.5 25.2 24.1 LSD: (0.05 = 1.8) ; (0.01 = 3.2)
D. Second 1 18.5 23.7 17.0 Day 2 23.5 23.0 20.3 Score LSD: (0.05 = 3.8) ; (0.01 = 6.5)
E. Total 1 71.2 70.7 64.5 Score 2 80.6 74.6 68.8
LSD: (0.05 = 3.0) ; (0.01 = 5.5)
* 1 Method of Qarooni et al (1987):roll gap 1.5mm, baking 400°C/90 sec. 2 Modified method: roll gap 1.lmm,baking 550°C/33sec.
** Table 1 Note Maximum potential scores: External (35), Internal (35), Second Day (30), Total (100).
79 Internal Score (Table 4.6C)
Method: There was no significant effect of baking method on the internal score for any of the three samples.
Sample: For both methods, sample A gave significantly higher
internal scores than either samples B or c. Sample A had good internal characteristics, whilst sample B had a dry
crumb (texture score 2.5) which was open in appearance and
was tough to tear (score 6.5). Sample C produced a ·woolly'
crumb that was moist, layers were uneven (score 2.8) and it
did not show sufficient resistance to tearing (score 6.5).
Interaction: No significant interaction between flour sample
and test method was observed.
Second Day Score (Table 4.6D)
Method: Sample A yielded significantly higher (P<0.05) second
day scores using the modified method. There was no difference between the methods for rating samples Band c.
sample: There were no significant differences between the
samples for each treatment. Sample B did not crack on rolling and folding, although it was tough to tear (score
6. 0) . Sample C had the lowest scores for both methods. This
bread cracked on rolling and folding and showed little resistance to tearing.
80 Interaction: The improved second day scores for samples A and c are consistent with the results from this study on dough thickness and temperature. Thinner doughs baked at higher temperatures had better keeping quality.
Total Score (Table 4.6E)
Method: Sample A had a significant increase in total score
(P<0.01) using the method proposed by this study. Both samples B and C showed significantly increased scores (P<0.05) using this method. For all three samples the improved bread quality using this method reinforces the evidence that baking thinner doughs at higher temperatures resulted in better quality Arabic breads. This improvement was largely expressed as an improved softness and flexibility of the breads on the first day and an improved keeping quality. The fact that there was no differences in bread moisture between breads produced by either method, indicates that other factors such as moisture distribution and bread structure may account for the observed quality differences.
Sample: When assessed by the method of Qarooni et al (1987), samples A and B did not have significantly different scores, whilst Sample C gave a significantly lower score (P<0.05) than the other samples. The modified method revealed differences which were significant (P<0.01) between samples A and B, and Band c.
81 Results for Sample A (protein content 11.1%, with moderate strength and moderate starch damage) indicated superior bread quality to either Sample B (low protein) or C (high protein). This is consistent with the findings of Williams et al (1988) and Qarooni et al (1988).
Interaction: There was a significant interaction between the samples and test method (P<0.01). The score of sample A had its score increased more than did samples Band C when baked with the proposed method. This resulted in a greater spread of scores which allowed better discrimination between these samples using this test method.
4.3.3 Comparison of test baking method with a commercial bakery
To test the relevance of the test baking method to commercial baking, three flour samples of different protein contents (8.5, 11.2 and 13.0%), were test baked and baked in a fully automated Arabic bread plant. The baking process of the commercial bakery was different to that of the test baking method. This included differences in formulation, mixing, proofing and baking, however no further details of the process will be presented in the interests of the bakery's confidentiality.
Each flour was baked in duplicate both using the test baking method and the commercial bakery. The results were then analyzed using a two way analyses of variance. The results
82 are discussed in terms of each bread parameter.
Bread area: There was a significant difference between flours
(P < 0.01) and a significant interaction between baking method and flour (P < 0.01). The interaction emphasizes an important difference between the procedures. In the commercial bakery the roll gaps are adjusted for each dough to give the correct bread diameter to suit the packaging, whilst for the test baking method the gaps are constant for each flour. With the test baking method the low protein sample had the largest area and the high protein sample the smallest area. For the commercially baked samples the areas were similar for all flours.
Bread shape: For both baking processes, the bread from the moderate protein sample was of better shape than for the other samples. The differences were clearer for the test baking method where the low protein sample produced distinctly oval breads and the high protein samples resulted in triangular breads. This difference between methods was again due to the difference in sheeting procedures.
Smoothness and Cracks: No significant differences observed.
Crust colour: No significant differences observed.
Blisters: Very few blisters observed.
83 Ability to roll and fold: The low protein sample achieved the lowest scores under both bakery regimes (Table 4.7A).
Quality of separation: Some of the high protein samples did not pocket completely when baked with the test baking method, no such observation was made for the commercial bakery.
Crumb texture: The crumb texture was poorest for the low protein sample, although this occurred for both baking regimes it was more pronounced for the test baking method.
Crumb appearance: The crumb appearance of the low and high protein samples were both poor compared to the moderate protein sample when baked by either regime.
Evenness of layers: No significant differences observed.
Tearing quality: The low protein sample achieved the lowest scores for tearing quality for both baking regimes (Table
4. 7B) .
Second day ability to roll and fold: The moderate protein sample achieved the highest scores under both bakery regimes
(Table 4.7C).
Second day tearing quality: as above
84 Table 4.7 Selected baking scores from bread baked by the test baking method and by a fully automated bakery.
Flour Sample low medium high protein protein protein Baking regime
A: Ability to roll and fold Test Baking 4.5 8.5 7.9 Commercial Baking 7.5 9.0 8.5
LSD (0.05 = 1.47)
B: Tearing quality Test baking 5.0 7.9 7.0 Commercial baking 4.5 7.0 6.8
LSD (0.05 = 1.0)
C: Second day ability to roll and fold Test baking 9.0 14.5 13.5 Commercial baking 12.0 13.3 12.5
LSD (0.05 = 2.1)
D: Total score Test baking 60.7 78.4 68.9 Commercial baking 63.6 75.2 70.2
LSD (0.05 = 7.1)
Maximum Scores: ability to roll and fold, 10; tearing quality, 10; second day ability to roll and fold, 20; total, 100.
85 Total Score: Under both baking regimes the ranking of the samples was the same (Table 4.7D). The test baking method resulted in greater differentiation between samples, due largely to the different sheeting treatments of the two baking regimes. The extra differentiation could be considered an advantage as it makes the test baking method more discriminating. A possible disadvantage is that the test baking method may not predict exactly what will happen in the automated system, however this could be overcome by adjusting the test baking method to suit particular commercial bakeries. For example the formulation could be adjusted, the roll gaps could be varied or proof times changed. This would only be applicable if specific studies were being done for a particular bakery, otherwise a more general and discriminating process as presented by this study is more useful.
86 4.4 Effect of Baking Conditions and Dough Thickness on the starch Gelatinization and Bread Structure of Arabic Bread
In the previous section the effect of baking conditions and dough thickness on the quality of Arabic bread was investigated, in this section the same baking variables were examined for their effect on starch gelatinization and loaf microstructure. The same sets of conditions were used as described in Section 4.3, although only the more extreme sets of conditions were studied.
4.4.1 Light microscopy
Effect of dough thickness: Photomicrographs of the upper layer of loaves produced from doughs sheeted to 1.5mm and 1.0mm and baked at 400°C for 90 sec are presented in Plates 4.1 and 4.2 respectively. For both treatments, there was a thin layer on the upper surface of the sections which largely consisted of densely packed birefringent starch set in a protein matrix. The lack of starch gelatinization indicates that this layer dried out before either gelatinization or cell expansion could take place. Dense packing of starch and lack of voids in this layer, must form a barrier of reduced permeability, which traps the expanding gases during pocketing.
87 Plate 4.1 Photomicrograph of cryostat section of the top layer of Arabic bread, baked with a dough thickness of 1.5mm at 400°C for 90sec. Stained with Ponceau 2R and viewed under cross polars and a quarter wave plate. Bar=lOOµm; (B) birefringent starch; (C) crumb cell; (Cs) crust surface.
Plate 4.2 Photomicrograph of a cryostat section of the top layer of Arabic bread, baked with a dough thickness of 1.0mm at 400 °C for 90sec. Stained with Ponceau 2R and viewed under cross polars and a quarter wave plate. Bar=lOOµm; arrows def ine crust width; (C) crumb cell; (Cr) crumb.
88 The bread below the crust was defined as the crumb. It consisted of a protein matrix set with starch which had almost entirely lost birefringence. This layer contained many voids which represented the cell structure of the bread.
The cells were generally ovoid, and they increased in size from those adjacent to the crust. At the internal surface of the crumb, the cells tended to be torn open. With the increase in cell size there was a corresponding decrease in cell wall thickness. For the thicker breads, this meant they had a higher proportion of larger cells than the thinner breads. However no quantification of these observations was made.
A further difference between the dough thickness treatments was the thickness of both the crust and crumb layers.
Measured at a magnification of lOOX, the crust thickness
(average of 10 observations), for the 1.5mm, 400°C/90sec bread was 0.42 ± .007mm and for the 1.0mm was 0.2 ± .006mm.
The corresponding crumb thickness was 3.8 ± .036mm for the
1.5mm bread and 2.1 ± .074mm for the 1.0mm bread.
It is suggested that the differences in crust thickness and crumb structure between these treatments is due to a difference in heat transfer as the doughs are baked. The difference in crumb thickness is expected, and is another measure of the different surface area to volume ratio previously discussed (section 4.3.1).
89 Effect of baking conditions: Higher baking temperature resulted in a thinner layer of birefringent starch on the upper surface for all dough thicknesses (Plates 4.3 and 4.4). For the 1.5mm doughs, this layer was 0.45 ± .007mm at
400°C/90 sec and 0.15 ± .005mm at 600°C/21 sec and for the 1.0mm doughs this was 0.20±.006mm at 400°C/90sec and 0.08±0.00Jmm at 600°C/21sec. The crust must form more rapidly the higher the baking temperature, resulting in less overall moisture loss. At 400°C only a single layer of birefringent starch was observed, at 600°C, a second layer occurred for all dough thicknesses. This second layer was on the upper surface of the cells adjacent to the crust, approximately 0.06 to 0.1mm below the crust for the 1.5mm doughs. It is suggested that the heat at 600°C causes rapid drying on the upper surface of the cells near the crust, therefore reducing the moisture available for gelatinization.
The cells of the breads baked at 600°C/21sec appeared to be larger than those baked at 400°C, although this was not quantified.
Bottom layer: Sections were also taken from the bottom layer of loaves for the above treatments. The pattern of gelatinization was similar to the upper layers as were the crust and crumb structures. This observation is different to that of Qarooni (1988a). He found that for bread baked at 400°C for 90sec, there was no layer of ungelatinized starch. This difference in observations between the studies may be attributed to the difference in where the sections
90 were sampled from. Qarooni (1988a) sampled sections from the centre of the bottom layer which remains in contact with the hot plate for the duration of baking. In the present study sections were taken from half way between the edge and the middle of the bottom layer. On baking this part of the loaf lifts off the hot plate as pocketing occurs.
91 Plate 4.3 Photomicrograph of a cryostat section of the top layer of Arabic bread baked with a dough thickness of 1.5mm at 600°C for 21sec. Stained with Ponceau 2R and viewed under cross polars and a quarter wave plate. Bar=lOOµm; Arrow marks upper cell surface, (Ct) crust.
Plate 4.4 Photomicrograph of a cryostat section of the top layer of Arabic bread baked with a dough thickness of 1.0mm at 600°C for 21sec. stained with Ponceau 2R and viewed under cross polars and a quarter wave plate. Bar=lOOµm; Arrow marks upper cell surface; (Ct) crust.
92 4.4.2 starch gelatinization
The photomicrographs (Plates 4.2 and 4.4) show the majority !)t"Q.I'\"' J. s of the starch>to have lost birefringence. This observation confirms that of Qarooni (1988a). However it is not possible to tell from these sections whether there is any effect of dough thickness or baking conditions on the extent of gelatinization. In an attempt to quantify potential differences, starch was extracted from these bread treatments and its susceptibility to glucoamylase activity measured. The susceptibility of starch to glucoamylase measures a later stage of gelatinization than the loss of birefringence (Goering et al 1974). Measurement of the glucoamylase susceptibility therefore may show differences in the extent of gelatinization not observed by light microscopy.
Measurement of the susceptibility to glucoamylase of starch extracted from both the upper and lower layers of Arabic bread indicated that the majority of starch was gelatinized. This supports the observations made with light microscopy. Measurements ranged from 82.5 to 91.6% (Table 4.8). The extent of gelatinization was significantly lower for the
breads baked at 600°C/21sec than for those at 400"C/90sec
(F1 , 8 : P<0.05). There was no significant effect of dough thickness.
The extent of starch gelatinization was similar to Baladi bread, which was baked with a higher moisture content, using a similar approach (Faridi and Rubenthaler, 1984b). Results
93 from this technique must be interpreted with some caution because the measurements were made on extracted rather than total starch. Using a similar extraction method, Lineback and Wongsrikasem (1980) found only 58% of total starch to be extracted. So whilst a difference has been found between treatments, no statements can be made regarding the total starch.
Table 4.8 Percentage of starch susceptible to glucoamylase activity for dough thickness and baking condition treatments.
Baking conditions 400°C/90sec 600°C/21sec
Roll gap
1. 5mm Rep 1 88.3 82.5 Rep 2 91. 6 88.2 Rep 3 87.0 87.0 Mean 89.0 85.9
1. 0mm Rep 1 89.7 86.9 Rep 2 90.8 83.0 Rep 3 86.9 84.8 Mean 89.1 84.9
LSD (P=0.05: 4.6)
4.4.3 Electron microscopy
A scanning electron microscope combined with a freeze fracturing technique for sample preparation was used to examine bread microstructure and starch gelatinization. This allowed the examination of specimens at high
94 magnification with minimal disturbance to their structure. The freeze fracture technique used in this study looks directly at the fractured surface rather than a shadow of the surface as described by Fretzdorf et al. {1982).
Not all treatments were examined by this method and most of the discussion is focussed on bread from 1.5mm doughs baked
at 400°C/90sec and 1.0mm doughs baked at 600°C/21sec as these represent the more extreme treatments.
Plate 4.5 shows an overview of a specimen from the 1.0mm,
600°C/21sec treatment. Across the top layer there was a solid block, this appears to equate to the crust identified in the
light microscopy. A similar layer was observed for all
treatments examined. This layer is also shown in Plate 4.6 which is of the upper surface and was seen to consist of well
defined, intact starch granules. The upper surface of the
crust is shown at a higher magnification in Plate 4.7. The
starch granules are clearly defined and appear intact. At
yet a higher magnification and looking at a cross section of
the crust {Plate 4.8), type A and type B starch granules can
be identified and protein fibrils running between the granules can also be identified.
Looking at the crumb in Plate 4.5, the observation of cell
size increasing from those adjacent to the crust, to those at the interior crumb surface made from the light microscopy, was confirmed. Cells are generally ovoid and are torn open at the internal surface as described.
95 .~- . ~.-:.. ' . . \ Plate 4.5 Scanning electron micrograph (S.E.M.), cross section of the upper layer of Arabic bread baked with dough thickness of 1.0mm at 600°C for 21sec. The bar represents 500µm; arrow marks crust; (Is) internal surface of crumb; (Cc) crumb cell.
\7' ' . I Plate 4.6 S.E.M. cross section of the upper layer of Arabic bread baked with dough thickness of 1.0mm at 400 °C for 90sec. The bar represents lOOµm; (Cr) crumb; (Cs); crust surface.
96 Plate 4.7 S.E.M. crust surface of the upper layer of Arabic bread baked with dough thickness of 1.0mm at 400°C for 90sec. The bar represents 20µm; (A) type A granule; (B) type B granule.
Plate 4.8 S.E.M. cross section of the crust of the upper layer of Arabic bread baked with dough thickness of 1.0mm at 600 °C for 21sec. The bar represents 25µm; (A) type A granule; (B) type B granule; (P) protein.
97 In many of the cells near the crust of the 1.0mm, 600°/21sec treatment, starch granules on the upper cell surface were still intact, whilst on the lower cell surface there was folding and collapse of granules (Plate 4.9). In the bottom half of the crumb, the starch in the surfaces of the cells appeared fused with the outline of individual starch granules difficult to define (Plate 4.10).
For the 1.5mm, 400°C/90sec treatment, the overall bread structure appeared similar with the crust layer identified, and the increase in cell size from those adjacent to the crust to the interior crumb surface was observed (Plate 4.11). However the difference between the treatments appeared to be in the extent of starch fusion or pasting in the cells adjacent to the crust. Once below the crust, most of the cell surfaces had fused starch structures (Plate 4.12). This represents a high degree of starch gelatinization and it was higher again towards the interior surface of the sample (Plate 4.13).
From these observations no quantification of the differences observed between the treatments was made. However the 1%. observations do suggest that the extent of gelatipation was less in the 1.0mm, 600°C treatment. This supports the results obtained from the glucoamylase measurements of extracted
98 Plate 4 . 9 S. E .M. i nternal s u rface of a crumb cell , a djacent to the crust, the upper layer of Arabic bread baked with dough thickness of 1.0mm at 600 °C for 21sec. The bar represents 50µm; (Fs ) fused starch; (Sg) starch granules.
Plate 4 . 10 S.E.M. surface of a crumb cell near the interio r surface of the upper layer of Arabic bread baked with dough thickness of 1.0mm at 600 °C for 21sec. The bar represents 50µm.
99 ~ Af · -
Plate 4.11 S.E.M. cross section of the upper layer of Arabic bread baked with dough thickness of 1.5mm at 400°C for 90sec. The bar represents 500µm; arrow marks crust; (Is) interior surface; (Tc) torn open cell.
Plate 4.12 S.E.M. crumb cells adjacent to the crust of the upper layer of Arabic bread baked with dough thickness of 1.5mm at 400 °C for 90sec. The bar represents lOOµm.
100 Plate 4.13 S.E.M. surface of crumb cells near the interior surface of the upper layer of Arabic bread baked with dough thickness of 1.5mm at 400 °C for 90sec. The bar represents lOOµm.
4.3.4 General discussion
In this section, the observations concerning the effect of dough thickness and baking conditions on bread score are discussed in the context of the information on bread microstructure and starch gelatinization.
Thinner breads baked at higher temperatures for shorter times produced the best quality breads. The effect of thinner doughs was to reduce the thickness of the crumb and crust whilst increasing the surface area leading to a greater moisture loss during baking. Higher baking temperature reduced mo i sture loss a nd i n fact reduced crust thickness as
101 well. This was associated with superior rolling and folding and tearing quality on the second day. These quality differences must result from a combination of crust and crumb structures and the different moisture contents. crust: For Arabic bread there is a distinct crust and crumb. The crust has a dense structure containing ungelatinized starch. Immediately after baking the crust is dry and brittle, as the bread cools, the crust becomes more flexible. Other reactions that take place in the crust which further distinguish it from the crumb are those of caramelization and maillard reactions (Bertram, 1953). When tearing Arabic bread it is observed that the outer surface (crust) cracks easily, and that it is the crumb which maintains integrity, providing the elasticity and strength of the loaf.
Crust thickness was influenced by the above treatments. The crust was thickest for 1.5mm doughs baked at 400°C/90sec and thinnest for 1.0mm doughs baked at 600°C/21sec. The thickness of the crust would influence moisture distribution because after baking moisture moves from the crumb to the crust. For Arabic bread this is more significant than for pan bread because there is less total crumb moisture and the crust to crumb ratio is higher. Therefore breads baked at lower temperatures which have a greater moisture loss during baking, would also lose more moisture from their crumb due to moisture redistribution after baking. As moisture content is related to bread firming for pan bread (Rogers et al, 1988), it is expected that effects of dough thickness and
102 baking temperature on crust thickness and total moisture content could contribute to the difference in second day scores observed for these treatments. Nuclear Magnetic Resonance techniques may be the most reliable way to measure moisture distribution, , not used in this study.
Crumb: Crumb thickness affected the number of larger cells in the crumb. As thicker breads had lower second day scores, perhaps the combination of larger cells with thinner cell walls decreases bread strength. For pan bread a fine cell structure of small cells with thin cell walls produced bread with a soft texture (Taranto, 1983). Perhaps manipulation of the cell structure of Arabic bread could be used to extend shelf life by improving both the softness and strength of the crumb.
starch gelatinization: There appeared to be less gelatinization at higher baking temperatures. This was apparently due to the rate of heating and moisture loss of cell surfaces in the crumb nearest the crust. It is possible that the rate of retrogradation and moisture distribution may have been affected by the extent of gelatinization. Future study could measure the rates of gelatinization and starch retrogradation using differential scanning calorimetry.
The description of pocketing made by Mizrahi and Mizrahi (1988) can be enhanced by the observations of starch gelatinization and bread microstructure. By combining these
103 observations with the careful account of events which are known to occur during baking, the following explanation of pocketing is presented.
On entering the oven, the outer surface dries to form a thin skin (crust) of reduced permeability, evidenced by the fact that gas pressure is trapped within the structure. In the dough between the crusts, fermentation gases expand including dissolved carbon dioxide as it loses solubility. These expand the cell structure of the dough. At the same time steam is generated and the starch gelatinizes to set the expanded crumb structure. As total gas pressure increases it disperses through the now open cells until the pressure is high enough to separate the now "set" upper and lower layers, this optimally occurs in the centre, which is predicted to be the point of lowest resistance because the moisture content is highest, and the level of gelatinization low (as the temperature at this point is the lowest within the loaf). Expansion of the bread is limited by the strength and elasticity of the outer dry crust. Steam continues to be generated, and the gas pressure is finally released when a hole is formed in the outer crust, usually in the bottom layer. Baking is complete when the upper crust has developed sufficient colour, by which time the crumb starch is almost entirely gelatinized. The dryness of the outer skin and the gelatinized crumb holds the inflated structure in place. The initially brittle layers soften as moisture redistribution takes place and the structure may begin to collapse, however the bread is usually flattened for packaging before this
104 occurs. Once packaged, further moisture redistribution results in a crust that is soft and flexible.
In the abscence of specific evidence, it is proposed that for both Baladi and Arabic bread the cell structure combined with the expansion of both fermentation gases and steam contribute to pocketing during baking.
To prove this or to determine the relative contributions of the individual gases would require accurate measurement of temperature profiles within the loaf along with estimates of the carbon dioxide available as well as steam and gas pressures at these temperatures. Given the thickness of the bread and the rapid baking times, this would be difficult. Whilst it is of value to understand the pocketing process,
it may be unneccessary to measure the exact contributions of
individual gases, particuarly when there is no evidence to
suggest that such information would lead to improvements in
bread quality.
105 4.5 Flour Quality Tests For Selected Wheat Cultivars and
Their Relationship to Arabic Bread Quality
The purpose of this section was to establish whether there are varietal factors which influence Arabic bread quality, and to define the use of traditional flour tests for the assessment of flour for Arabic bread production. Such information is of direct assistance to wheat breeding programmes, and to wheat and flour purchasers and marketers.
The flour samples studied were derived from commercial wheat cultivars grown in Australia (Table 4.9).
Table 4.9 Description of wheat cultivars
Cultivar Grain Dough Commercial Hardness Strength Classification
Rosella Soft moderate ASW/A Soft Egret Soft weak A Soft Kulin Soft weak ASW Osprey Hard moderate ASW/AH Halberd Hard moderate ASW Minto Moderate strong ASW Hartog Hard strong AP/AH Banks Hard strong AP/AH Cook Hard strong AP/AH
AP = Australian Prime Hard AH = Australian Hard ASW = Australian Standard White A Soft = Australian Soft
106 Selected analytical, rheological and baking data of the 49 flour samples are presented in Appendix 3. Selection of appropriate field samples gave a broad range of grain hardness (particle size index) and protein content. All cultivars were white wheats and all samples were of well filled grain, milled to produce flours of low colour grade (less than 2.0). The falling number of all samples was above 360 seconds indicating soundness and freedom from weather damage. Samples were also checked for varietal identity.
No unusual aroma or flavour was detected for any of the bread baked from these flour samples.
4.5.1 correlation matrix
A correlation matrix for 17 flour characteristics, Arabic bread score and pan bread score, showed few significant correlations between flour characters and Arabic bread score (Table 4.10).
Those that were significant (P< 0.01) were interrelated. Particle size index showed the strongest correlation (r=-0.50) with Arabic bread score, indicating that the hard grained cultivars produced higher quality breads. This supports the observations made for the individual cultivars and those of Qarooni et al,(1988). Other significant correlations with Arabic Bread Score were: rnaltose(r=0.44), starch damage (r=0.5) and water absorption (r=0.45). These were also related to PSI, and were correlated to each other.
107 It should be noted that for pan bread, there were significant (P< 0.01) correlations for protein content (r=0.81), water absorption (r=0.44), development time (r=0.74), valorimeter (r=0.71) extensograph area (r=0.62), maximum resistance (r=0.40) and extensibility (r=0.87).
The strength and number of correlations between flour tests
and pan bread quality as compared to Arabic bread, suggest that these tests are more suited to the description of flour quality for the production of pan bread.
108 Table4.10 Correlation matrix between flour properties and test baking scores.
PSI FA FCG MF SD F No. !PT PH Pr IJA DT ST B vv EA MR E AB PB
Particle size index (PSI) 1.00 -0.84 -0.87 -0.75 0.37 -0.84 -0.32 -0.33 -0.35 -0.36 -0.50
Flour Ash (FA) 1.00 -0.28 -0.32 -0.30
Flour Colour Grade (FCG) 1.00 0.41 -0.30 0.30 0.30 0.30
Maltose Figure (MF) 1.00 0.91 0.69 -0.46 0.76 0.40 -0.28 0.44
Starch Damage (SD) 1.00 0.72 0.81 0.32 -0.31 0.51 Falling Number (F.No.) 1.00 -0.32 0.70 0.29 -0.28 0.32 0.33 Initial Paste Temperature (!PT) 1.00 -0.32 -0.57 -0.44 0.30 -0.47 -0.42 -0.38 -0.30 Peak Height (PH) 1.00
Protein (Pr) 1.00 0.44 0.79 0.32 ·0.64 0.77 0.58 0.34 0.81 0.81
Water Absorption (IJA) 1.00 0.51 0.37 ·0.60 0.60 0.27 0.45 0.44
Development Time (DT) 1.00 0.49 -0.66 0.93 0.65 0,45 0.76 0.74 Stability Time (ST) 1.00 -0.52 0.57 0.60 0.56 0.36 Breakdown (B) 1.00 ·0.84 -0.64 -0.54 -0.68 ·0.29 ·0.56
Valorimeter Value (VV) 1.00 0.72 0.55 0.78 0. 71
Extensograph Area (EA) 1.00 0.91 0.82 0.62
Maxil11UllResistance (MR) 1.00 0.61 0.40
Extensibility (E) 1.00 0.86
Arabic Bread Score CAB) 1.00 0.37 Pan Bread Score (PB) 1.00
Level of significance for correlation coefficients: P=0.01: 0.372 P=0.05: 0.282 -- not significant 4.5.2 Multiple regression
A multiple regression was performed using a selected linear regression model which accounted for 54 percent of variation. This involved both protein content and PSI in a quadratic equation (Arabic bread score = 32Protein 1.5Protein2 - 0.5PSI - 83.1). Further multiple regression analysis using best fit models did not yield useful prediction equations to explain the population variance. The only parameter in common between this equation and the prediction equation of Qarooni et al. (1988) was PSI.
When the prediction equation (Arabic bread score = 50.9-
0.94PSI 43.4Flour ash + 29.12Development time + O.OlViscograph peak height 3.41Development time2 .) of Qarooni et al. (1988), was applied to the data of this study there was a significant relationship between the predicted and actual total scores (r = 0.604, P $ 0.01). However, the regression only accounted for 35% of variability. This poor prediction was not unexpected. In the population the equation was derived from it accounted for only 74% of variability, and in this trial different flour samples and a different baking method were used.
4.5.3 Arabic bread and flour protein content
4.5.3.1 Within cultivars
within wheat cultivars a strong relationship between protein
110 content and Arabic bread score was observed. For six of the cultivars there was a clear indication of a parabolic relationship where there was a protein optimum below and above which bread quality decreased (Figure 4.1). For the other cultivars tested, the number of samples or the protein range were insufficient to establish such relationships.
Samples with protein contents below the optimal level exhibited similar quality defects for all cultivars. Low protein samples had lower baking absorption and produced doughs which sheeted more thinly to give a greater surface area. On baking, these breads were harsh and dry with poor internal crumb texture and structure. They cracked on rolling and folding and in extreme cases they shattered.
For samples with protein contents above the optimal level, quality defects were also similar between the cultivars. The high protein samples were difficult to sheet as they shrank between each sheeting step. This resulted in poor shape and low surface area. The dough surface was rough, resulting in blistering and a rough external surface of the loaf. The crumb was sticky and in extreme cases the two layers adhered after baking. The crumb was also too open. On the first day, the bread was soft and flexible, however the bread deteriorated such that it cracked on the second day when rolling and folding, as well as losing resistance to tearing.
111 ROSELLA EGRET 85 85
75 75 Ill a: 0 • • 0 U) • • • 65 65 • 0 • • <( • Ill a: m • 0 55 55 iii <( a: <( • 45 45 •
8 10 12 14 8 10 12 14
85 BANKS 85 COOK • • • • 75 75 Ill • • • a: 0 0 • U) 65 • 65 • 0 < • • Ill a: m u 55 55 iii < a: < 45 45
8 10 12 14 8 10 12 14
HALBERD 85 HARTOG 85 • • • 75 75 UJ • • • a: 0 • u • • "' 65 65 . 0 • <( UJ a: Ill 55 55 ~ Ill < a: <( 45 45
8 10 12 14 8 10 12 14
FLOUR PROTEIN CONTENT (%) FLOUR PROTEIN CONTENT (%)
Figure 4.1 Relationship between the total score of Arabic bread and flour protein content for 6 wheat cultivars.
112 Protein content and quality affected sheeting thickness. High protein or strong flours produced thick doughs and low protein or weak flours produced thin doughs. Dough thickness was shown to affect bread quality (Section 4.3). The interaction between flour quality and dough thickness was discussed for the comparison between the test baking method and commercial practice, where differences in dough thickness resulting from flour quality were found to increase the differences between flours with the test baking method, thereby improving differentiation between samples.
4.5.3.2 Between cultivars
Optimal Arabic bread score and the protein content at which this occurred varied between cultivars and were; 72 at 11.6% for Egret, 73 at 11.4% for Rosella, 74 at 10.0% for Cook 77 at 9.8 for Halberd, 81 at 9.8 for Hartog, and 80 at 9.5 for Banks. These differences are discussed for the soft and hard grained cultivars under separate headings.
soft-grained wheats: The two softer grained cultivars, Rosella and Egret, required higher protein contents to achieve optimal baking quality compared to the harder grained cultivars. Across the protein range the baking quality of these soft grained cultivars was lower than for the hard grained samples. Both Rosella and Egret had low starch damage and low water absorption. The breads tended to be dry with poor crust colour and staled rapidly. Rosella showed better baking quality for the low protein samples than
113 Egret. This difference could be attributed to the stronger dough characteristics of Rosella.
Hard-grained wheats: Differences in quality were observed between the hard grained cultivars. Banks showed high baking potential and a good tolerance over a range of protein content. This variety is known for its balanced dough properties and it is likely that its strength combined with good elasticity made it well suited to the production of Arabic bread.
Above the protein content required for optimal baking in Hartog, the bread quality deteriorated rapidly. This is considered a result of 'over strong' dough characteristics at these protein levels. It is of interest to note that in both the present study and that of Qarooni (1988a), samples of Hartog with similar protein contents (10 and 9.8%), achieved the highest total bread scores.
Across the protein range, Cook was the least suited of the hard wheats to making Arabic bread. The doughs produced from this variety were over strong, making them difficult to sheet even at lower protein levels.
Halberd tended to produce doughs that were too weak, or at the higher protein contents, too short.
114 4.5.3.3 Combined sample set
When the data for all 49 samples were combined the relationship between bread score and protein content showed a similar trend to that found for individual cultivars, the curve of best fit being a quadratic. However, the curve only accounted for 38% of the population variance (Figure 4.2). That so little of the variance was explained emphasizes the differences observed between cultivars. A similar curve was presented by Qarooni et al (1988), however no supporting statistical parameters were provided. From a recalculation of the data it was found that the curve only accounted for 46% of the population variance which is similar to this study.
4.5.4 Pan bread and protein content
When the same samples were used to bake pan bread, the relationship between protein content and bread score was linear with a correlation coefficient of r=0.81 (P< 0.01), (Figure 4.3). A curve of best fit accounted for 64% of observed variance.
Clearly, compared to pan bread, factors other than protein content must be examined to understand the difference between cultivars and individual samples for Arabic bread quality.
115 85 •
75 UJ a: 0u ••... • CJ) ... • ... 65 • • • C ... <( • • w a: co u 55 co <( a: <( • 45 ...
8 10 12 14
FLOUR PROTEIN CONTENT (%)
Figure 4.2 Relationship between total Arabic bread score and flour protein content for 49 wheat samples. (o flour from hard wheat; • flour from soft wheat). Fitted ~urve, Arabic bread score= -83.1-0.5PSI+32protein -l.5protein.
85
• 75
UJ a: 0 u 65 en C <( UJ a: 55 IXl z <( c. 45 . •.
8 10 12 14
FLOUR PROTEIN CONTENT C%l
Figure 4.3 Relationship between pan bread score and flour protein content for 49 wheat samples.
116 4.5.5 Grain hardness
Given the correlation of grain hardness (PSI) with Arabic bread score, the sample set was divided into subsets of soft wheats and hard wheats.
4.5.5.1 Soft wheats
The soft wheats milled to give flours with low starch damage which results in low water absorption. This was indicated by the strong positive correlation between starch damage and water absorption (r=0.81, P<0.01). Low starch damage
results in pale crust colour due to the lack of available
sugars for caramelization. Lower water absorption of the flour, produced doughs low in,moisture which when baked gave dry, stiff breads of poor quality as discussed earlier for
the cultivars Rosella and Egret. These observations indicate that soft wheats are unsuitable for the production of Arabic
bread.
4.5.5.2 Hard wheats
The hard wheats milled to give higher levels of starch damage which resulted in water absorptions more suited to the
production of Arabic bread. With the higher levels of starch
damage, crust colour became a function of protein content as crust browning is dependent on both the caramelization and
Maillard reactions (Bertram, 1953).
117 When all samples with a grain hardness less than 20 were analyzed, a resulting population of 33 hard grained samples showed a significant (P< 0.01) quadratic relationship between protein content and Arabic bread score, where 56% of the population variance was accounted for by the following equation {Arabic bread score= 25Protein -1.3Protein2
48.9).
4 •.• 5.3 Correlation matrix for hard grained wheats
A correlation matrix was completed on the hard grained sample subset and some new factors emerged with significant {P< 0.01) relationships to Arabic bread score: protein content {r=-0.45), development time (r=-0.46) and valorimeter value(r=-0.45). These negative correlations suggest that for the hard grained wheats tested, the greatest limitation to bread quality was over strength. The greatest problem with over strength occurs in the sheeting process, with the bread
faults being similar to those associated with protein contents above the optimal levels.
Using this subset, correlation of the same factors to pan bread quality were strongly positive (P < 0.01): protein content {r=0.79), development time {r=0.69) and valorimeter value (r=0.65). This suggests that whilst high protein strength is desirable for pan breads, this is not the case for Arabic bread.
In earlier work at the Bread Research Institute of Australia,
118 Moss (1980) found reduced pan bread volume for flours with an extensograph resistance greater than 400 BU. It was possible to improve the volume of such over strong flour by increased dough development using a sheeted dough process. This process of dough development would not be practical for the production of Arabic bread, and experience suggests that development beyond their mixing requirement results in doughs which are too sticky for further processing.
4.5.S.4 Flour quality parameters
Using the hard grained samples a description of wheat and flour quality has been developed. For each character measured, a cut off value for bread score was defined at 75 points, above which the bread was considered to be of good quality. Each character was examined to see if there was a cut-off below or above which no samples scored above 75. An example involving protein content is provided in Figure 4.1. The ranges for optimal bread quality defined by this method are shown in Table 4.11. Within the range defined for each parameter, end product quality varies from poor to excellent. Within these ranges it is necessary to test bake a flour in order to determine its suitability for the production of Arabic bread. The baking potential of any samples outside the defined ranges is considered limited.
The range of quality parameters developed from this study supports the general descriptions provided by Qarooni et al. (1988), and Cornish and Palmer (1988). Hard grained, clean
119 milling wheats of moderate protein content and moderate dough strength appear to be the most suited to Arabic bread production. However this study emphasises that the baking potential of flours cannot be reliably predicted from wheat or flour quality tests, and to determine true baking potential, the sample must be test baked by a reliable method.
Table 4.11 Ranges of common wheat and flour tests for optimal Arabic bread quality
Test Range
PSI less than 20 Starch damage (%) 6.0 to 9.0 Protein content (%) 9.0 to 12.0 Farinograph Water Abs. (%) 58.0 to 65.0 Dev. Time (min) 2.0 to 5.0 stability (min) 3.0 to 8.0 Valorimeter value less than 60.0 Extensograph area (cm2 ) 60.0 to 125.0
120 4.6 Role of Flour Components for Arabic Bread
Flour quality has been shown to affect Arabic bread quality (Section 4.5). Differences in quality were attributed to factors such as grain hardness, protein content and genotype. However the flour component(s) responsible for these observed differences has(ve) not been identified. Using fractionation and reconstitution techniques it is possible to identify the contribution of components to product quality. Although it may be difficult to determine the interaction of components, the technique does provide a useful means for exploring differences in flour quality.
In this section, the role of the following flour components is investigated: lipid, water-solubles, starch and gluten.
Flour samples
Three flour samples were used for this study including samples of the two wheat cultivars Hartog and Halberd. The cultivar Hartog was shown to have a higher baking potential
for Arabic bread than Halberd (Section 4.5). A commercial bakers flour which was available in large quantities and was
considered well suited to the production of Arabic bread was also used. Analytical and rheological data for the three
samples is presented in Table 4.12.
121 Table 4.12 Analytical results of three flour samples.
Flour Commercial Hartog Halberd Bakers
Protein (%) 11.2 11.2 9.8 Maltose (mg) 1.9 3.6 2.4 Farinograph WA (%) 63.7 69.5 61.4 DT (min.) 5.1 5.5 4.3 Extensograph Max Res (BU) 340 320 310 Exten (mm) 233 222 170
4.6.1 Role of flour lipid
Baking trials were repeated in triplicate except for the lipid exchange and lipid sep,uation trials which were repeated in duplicate. Standard deviations for total bread score did not exceed ±3.1.
4.6.1.1 Baking absorption
Water absorption and mixing characteristics were examined for the commercial bakers flour. Mixograph development times were equivalent for the whole and defatted flours and the fully reconstituted flour (4.5 ± 0.2 min). This result was consistent with those obtained by MacRitchie and Gras (1973).
Farinograph water absorption of the defatted flour was 2.4 ±
0.3 percent greater than the whole flour and development time was 3.2 ± 0.2 min greater. Both water absorption and development time were equivalent between the whole flour and the fully reconstituted flour. It was noted that the
122 defatted sample appeared to stick to the blades of the farinograph such that even before the addition of water, the farinograph recorded a greater resistance, this would account for the higher water absorption. Accordingly higher Farinograph peaks for the defatted flours were recorded, the same water addition was used for whole, defatted and reconstituted flours. This was because the higher resistance to mixing of the defatted samples was not considered to be a function of moisture content.
4.6.1.2 Reconstitution of flour with parent lipid
Each of the three flours (Table 4.12), were defatted with chloroform. Lipid from each flour was added back at two levels, approximating 50 % and 100% of the original lipid content of the flour.
Dough Characteristics: Doughs prepared from the defatted flours were stiff, sticky and appeared to lack elasticity. Extensograph maximum resistance increased by 180 BU and extensibility decreased by 42mm when the flour was defatted. When lipid was reconstituted at 50% the "feel" of the dough improved, and at 100% the dough had similar handling characteristics to the whole flour.
After final proofing, samples of dough from the defatted flour and the whole flour were cut with a scalpel and cross sections were examined with a stereomicroscope (magnification
123 20x). No differences in cell structure were observed. It is possible that differences may have been identified with cryostat microtome sections viewed at higher magnification.
These observations indicate that although wheat lipid was an important component for dough development, it did not appear to affect the proofed dough structure.
Baking:
Total bread scores ranged from 63 to 81.7 (Figure 4.4). For each flour, the defatted samples gave the lowest baking scores. Reconstitution of 50% lipid resulted in higher scores and at 100% addition baking scores approximated those of the whole flour.
Zero lipid: Defatted flours without lipid addition baked to give breads of poor quality. The faults were consistent for each of the three flours and the most notable features were:
1) Smaller bread area and poor shape, faults that could be attributed to the observed stiffness of these doughs.
2) Dark crust colour and the occurrence of a type of blister on the upper crust which had not been observed with whole flour. The upper surface was covered with small (1 to 2mm diameter) white blisters that did not burn as do the usual blisters on the surface of Arabic bread.This suggests that they occurred in the later stages of baking. It was noted that loaves made a popping noise as they were removed from
124 the oven which appeared to be a result of the blisters bursting.
3) The bread "pocketed" as expected during baking. However after flattening for packing two hours after baking, the two layers stuck to each other, and were difficult to separate.
4) Crumb texture was sticky, which was consistent with the fusion of the layers.
5) The colour of the crumb was very white, which is consistent with the removal of pigments with the lipid,and was also very open, appearing as if all the cells had been torn open, with some holes in the crumb that extended through to the crust.
Although the bread was of undesirable quality, acceptable scores for ability to roll and fold, tearing quality and second day scores for all three flours were still achieved.
Fifty percent lipid: At a 50% level of lipid reconstitution, bread scores improved for all flour samples (Figure 4.4). Most of the features described for the defatted flours were still apparent, but to a lesser degree. The small surface blisters were present but they were fewer and tended to be smaller. The crumb was sticky but not enough to fuse the layers together. The crumb structure remained open but not as much as for the defatted sample. Second day scores were not significantly different to those of the whole flour for
125 all three samples (P< 0.05).
One hundred percent lipid: Full reconstitution of lipid resulted in bread quality that was indistinguishable from bread baked from whole flour for the Hartog and Halberd samples. For the commercial bakers flour, there were no obvious faults associated with the fractionation and reconstitution, however the total score was lower than for the whole flour (P< 0.1).
ARABIC BREAD SCORE 85.------~
80
75
70
60 DEFATTED FLOUR DEFATTED FLOUR DEFATTED FLOUR WHOLE FLOUR NO ADDED LIPID PLUS 50% LIPID PLUS 100% LIPID (CONTROLS)
- Halberd a Bakers D Hartog - Bakers + soy
Figure 4.4 Effect of levels of lipid reconstitution on the baking scores of three flours.
Many effects of defatting became apparent after baking. The open crumb structure and crumb stickiness suggested that
dough cells expanded with less resistance and burst,
126 resulting in large open holes in the crumb, compared to the fine even cell structure produced from whole flour. It is expected that the stickiness was a result of the changed crumb structure and altered moisture distribution. The surface blisters may be a result of a combination of factors such as, weakness in the upper crust and changes in the dynamics of internal gas pressure due to the open cell structure.
These results contrast with those found for pan bread, where flours defatted with either petroleum ether or chloroform produced similar loaf volumes to their control flours, and had fine crumb structure (Pomeranz et al., 1968; MacRitchie and Gras, 1973). The differences observed between these bread types may be due to the difference in baking conditions. In the present study Arabic bread was baked at 550°C for 33 sec. The high baking temperature resulted in far more rapid cell expansion and starch gelatinization than for pan bread. It is proposed that this rapid expansion placed a greater strain on cell structure and therefore a greater need for lipids to stabilize the cell structure. This supports the earlier descriptions of lipid function (MacRitchie and Gras, 1973; Wehrli and Pomeranz, 1970), but indicates that the lipids may have a more functional role in Arabic bread than in pan bread.
Rolling and folding, tearing quality and second day scores were lower but still acceptable for breads baked from defatted flour. It appears that whilst crumb structure may
127 play some role in determining these features, the nature of the gelatinised starch may be a more important determinant (assuming this is unchanged in the defatted state).
When lipid was reconstituted at 50%, Arabic bread quality improved. This is in contrast to the results of MacRitchie and Gras (1973) who found pan bread loaf volume was decreased and crumb structure was coarse. However another study which repeated this experiment obtained a different response (Chakraborty and Khan, 1988). This difference in results for pan bread could be either due to the flour samples or differences in baking methods. Given that the results of the present study were consistent for the three flours it is more likely that the different response observed for Arabic bread was due to the different baking conditions.
The restoration of bread quality with the reconstitution of all the chloroform-extracted lipid, indicates that this method of fractionation and reconstitution worked successfully with Arabic bread.
4.6.1.3 Bread quality of reconstituted lipid fractions
Polar lipid: The polar lipid was difficult to disperse as it was viscous and sticky. After dough mixing, spots of lipid were visible and even after sheeting some spots were apparent. The dough had a similar "feel" to dough prepared from the whole flour. Overall the bread quality was similar
128 to that of the whole flour with a total score of 77.8. Some notable features which distinguished the polar lipid reconstitution from the whole flour were: a small number of the white blisters; a whiter crumb colour and a slightly more open crumb structure.
Nonpolar lipid: Reconstitution of nonpolar lipid resulted in dough and bread which was difficult to distinguish from those made from the whole flour. The total score for this treatment was 78.5.
Reconstitution with both polar and nonpolar wheat lipids restored the baking potential of defatted flour. This observation is clearly different to those for pan bread where polar lipids are found to enhance loaf volume and nonpolar lipids depress loaf volume (MacRitchie and Gras, 1973; Ponte and De Stefanis, 1969). This supports the suggestion that the function of flour lipids in the baking of Arabic bread is different to that in pan bread.
4.6.1.4 Addition of soy oil to defatted flour
Soy lipid was added to the defatted commercial bakers flour at 50% and 100% of the extracted lipid level. At 50% the total score was lower than for the defatted flour with no added lipid (Figure 4. t·). All the faults were consistent with the defatted flour. The small surface blisters occurred along with fusion of the layers, sticky crumb and an open crumb appearance. At 100% lipid addition the faults
129 had improved, however the total score was below that of the 50% addition of wheat flour lipid. Blistering occurred to a lesser extent, the layers stuck together but were easier to separate and the crumb was less sticky and less open.
4.6.1.5 Addition of wheat lipid and soy lipid to whole flour
Wheat lipid and soy lipid were each added to the commercial bakers flour at levels of 0.5% and 1.0% of flour weight. Total scores ranged from 77.4 to 81 for the four treatments. None of these treatments resulted in significantly different bread scores to the original flour (P <0.05). It was noted that where lipid addition did result in higher second day rolling and folding scores, the second day tearing score was lower, resulting in no significant difference between second day scores (P ~0.05). Qarooni et al. (1989b) did find a small improvement in keeping quality with the addition of 0.5% and
1.0% shortening. This difference could be due to either the differences in test baking methods or the subjective nature of the scoring of bread quality.
4.6.1.6 Exchange of lipid fractions between flour samples
Each flour (Table 4.12) was defatted and baked with lipid extracted from the two other flours at approximately the original lipid content.
For each of the flours tested, no significant difference was found between the total score for the whole flour, defatted
130 flour reconstituted with native lipid or defatted flour reconstituted with either of the two foreign lipids (P <0.05). For example, defatted Halberd flour baked with either lipid from the commercial flour or from Hartog was no different to when baked with its own lipid.
Each of the three flours in this study gave bread of different quality. The Hartog sample achieved the highest scores and Halberd the lowest. The exchange of chloroform extracted lipid between these samples did not account for the difference observed in overall baking quality (total score).
Hartog flour had higher second day scores than the other flours (P ~0.05). When defatted Hartog flour was baked with Halberd lipid fraction the second day score was significantly reduced (P<0.05). Whilst this result does not clearly attribute the differences between these flours to their lipid content, it may account for some of the observed differences. Previous lipid exchange trials for pan bread have also not explained differences in loaf volume potential of the flours (MacRitchie, 1978).
4.6.1.7 TLC
TLC was used to compare the lipid extracted from the commercial bakers flour polar and nonpolar fractions of this lipid and soy lipid C , ·, '-~ 4. ,:.· ) . A reasonable degree of separation of the flour lipid into polar and nonpolar fractions was achieved when compared to that of MacRitchie
131 (1977). The results for the soy lipid were consistent with those of Eckly (1954) which indicate that it is composed predominantly of triglycerides.
Soy lipid did not fulfil! the role of wheat lipid in restoring bread properties. This is similar to previous results for pan bread where maize oil was used (MacRitchie, 1977). This was attributed to the low ratio of polar to nonpolar lipids in the maize oil. In the case of Arabic bread, this explanation would not be sufficient as wheat nonpolar lipids improved bread score. The TLC results showed that the wheat nonpolar lipid had a higher proportion of free fatty acids than the soy lipid c· f'i.: ,r.,3 4. !lf) • This difference in composition of the lipid may explain the inability of soy lipid to restore the baking potential of defatted flour.
132 Pp
'- ·-·-- Plate 4.14 Thin-layer chromatograms of; (W) whole wheat flour lipid, solvent chloroform; (N) nonpolar lipid, solvent chloroform; (S) soy lipid, solvent chloroform; (C) chloroform; (Wp) whole wheat flour lipid, solvent petroleum ether; (Np) nonpolar lipid, solvent petroleum ether; (Pp) polar lipid, solvent petroleum ether.
4. ,. 2 starch, Gluten and water-solubles
Baking tests were performed in duplicate and comparisons of treatments performed using analysis of variance.
Fractionation
Three flour samples (Table 4.12 ), were fractionated and information on the fractions is presented in Table 4.13.
133 Table 4.13 Protein content and ratio of fractions derived from three flour samples.
aProtein bweight of Fraction Content Fraction (%)D.M.B. (%)
Gluten Bakers 73.0±1.0 16.9±1.0 Hartog 75.0±0.8 14.8±0.5 Halberd 73.0±1.0 15.0±1.0 Starch Bakers 0.8±0.1 77.5±1.0 Hartog 1.1±0.1 79.0±1.0 Halberd 0.5±0.1 78.8±1.5 Water solubles Bakers 16.1±0.2 6.0±0.5
amean of 3 measurements bmean of 6 measurements
4.6.2.1 Role of water-solubles
When separating the starch and gluten components by the
method used in this study, 2.8L of water was used for each
400g of flour. Therefore to obtain the water-soluble
fraction, a large volume of water must be removed without
damaging the fraction. This required a lot of freeze drying capacity that was difficult to obtain. An experiment was designed to determine if the water solubles could be left out
of reconstituted samples and replaced by "synthetic yeast
food", as suggested by MacRitchie {1984).
After fractionation, the Bakers flour was reconstituted with and without the water-soluble fraction. The starch and gluten
134 without water-solubles was baked on its own, and with an enriched formula of 3% sugar, 0.5% malt flour and 0.5% ammonium chloride.
The reconstituted sample of starch and gluten without the addition of water-solubles had a low protein content and low maltose value (Table 4.14). Dough prepared from this sample was tight and felt dry, as a result it was difficult to round. The bread had uneven edges, pale crust colour, was stiff to handle and had very little crumb structure. With an
Arabic bread score of 66.2 ± 2.5, it was considered an unacceptable reconstitution.
When the starch and gluten were reconstituted with the enriched formula, the dough still felt stiff and dry. However the bread was an improvement on the starch and gluten recombination. Crust colour was acceptable, although still pale, the bread was soft and flexible on the first day and there was some cell structure evident in the crumb although this was poor and presented as a flat scaly crumb similar to bread made from a low protein flour. This treatment scored
72.5 ± 2.5, which was also considered unacceptable.
When starch and gluten were reconstituted with the water soluble fraction, the sample had a similar protein content and a higher maltose value than the original flour (Table
4.14). Dough behaviour was similar to that obtained with the whole flour, however it was not quite as smooth. The bread produced from this dough was of similar quality to the
135 bread produced from the whole flour, although the crust colour was still pale. The Arabic bread score for this reconstituted sample was 76.8 ± 2.5 compared to 78.9 ± 2.5 for the whole flour.
Table 4.14 Protein content and maltose values for selected reconstituted flours.
Protein Maltose Content Value Sample (%) 13.5 m.b. (mg g-1)
Bakers flour 11.2 1.9 Bakers gluten+ Bakers starch + aws (11% sample) 11. 3 2.3
Bakers gluten+ Bakers starch 10.5 0.7
aBakers water-soluble fraction
It appears that some improvement was obtained by the addition
of yeast food to the starch and gluten. This suggests that
one role of the water-solubles is to contribute to gas
formation as observed by Hoseney et al.(1969a). Even with the
enriched formula, the dough and bread were not as good as when the flour was reconstituted with the water-soluble
fraction. This could be because either the yeast food was
not adequate or the water-solubles have another role. The
tight, stiff, doughs resulting from starch and gluten without
water-solubles suggests that gluten behaviour may be modified by this fraction. Again this observation is in keeping with that of Hoseney et al.(1969a).
136 From these results it was decided that for any further study of the gluten and starch fractions, the water-soluble fraction would need to be included. No further attempt was made to define the role of the water-soluble fraction or to exchange this fraction between flours. This was largely due to the freeze drier capacity required to work with this fraction.
4.6.2.2 Role of starch and gluten
Protein content
Using fractions from the Bakers flour, samples were reconstituted to different protein levels by adjusting the gluten content. The Bakers flour when reconstituted to 9, 11 and 13% protein required, 55, 55.6 and 56.5% water addition, whilst mixing times for these samples were, 3.5, 4.0 and 4.5 min. Any differences in the baking quality of these flours could be directly attributed to their different quantities of gluten.
These samples were test baked in duplicate. A summary of the individual loaf quality parameters and their relationship to protein content for these samples follows.
Bread Area: Nine percent protein resulted in larger bread areas than the 13% sample (P < 0.05). This is consistent with earlier observations for flour protein content (Section 4.5.3).
137 Bread Shape: Although shape was not significantly different, there was a trend for the 9% samples to produce oval breads and for the 13% samples to have a slightly triangular shape, whilst the 11% samples were round.
Bread Smoothness and Cracks: Nine percent protein samples had significantly smoother surfaces than the high protein samples
(P < 0.01). The high protein sample resists sheeting and tends to catch and tear on the sheeting rolls causing a dimpled surface.
Crust Colour: All the reconstituted samples had pale crust colour. This suggests some change to the fractions resulting from the process of fractionation and reconstitution.
Crust Blisters: No samples had blisters.
Ability to Roll and Fold: Although there was no significant difference between the samples, it was noted that the 9% protein samples were not as soft.
Quality of Separation: The 9 and 11% samples pocketed without any problems, however for the 13% sample, some loaves had incomplete pocketing. This seems to be a result of tearing during sheeting.
Crumb Texture: The crumb texture of the 9% sample was dry and harsh, achieving significantly lower scores than the
138 other treatments (P < 0.05).
Crumb Appearance: The 11% sample achieved significantly higher scores than the 9 or 13% samples for crumb appearance
(P < 0.05). The crumb of the 9% sample was flat and scaley, whilst that of the 13% sample was too open and uneven.
Evenness of Layers: No significant difference was found.
Tearing Quality: The 11% sample achieved higher scores than either the 9 or 13% samples (P < 0.05). The 9% sample tended to be tough to tear whilst the 13% sample was too easy to tear.
Second Day Ability to Roll and Fold: There were no significant differences.
Second Day Tearing Quality: No significant difference although the 9 and 13% did show similar trends to those of the first day tearing quality.
Total Score: The 11% sample achieved a similar score (76.8 ±
2.0) to the whole flour(78.9 ± 2.5), whilst the 9% (70.7 ±
2.0) and 13% (70.9 ± 2.0) samples were both significantly
less (P < 0.01).The faults for the 9 and 13% samples occurred
for similar characteristics but were expressed differently.
139 Exchange
Flours were reconstituted with native starch and gluten to original flour protein contents, with the water-soluble component from the commercial bakers flour and mixographs were performed. The results indicated that the mixing characteristics of the reconstituted flours were similar to those of the whole flour (Table 4.15). This also indicated that the use of the water-soluble fraction from a single source could replace the native water-solubles of a flour sample for reconstitution.
Table 4.15 Mixograph results for re.constituted and whole flours.
Flour Mixing time (min.)
Bakers gluten + Bakers starch+ 1ws 3.3 ± 0.1 Bakers flour 3.1 ± 0.1
Hartog gluten + Hartog starch+ ws 3.8 ± 0.1 Hartog flour 3.7 ± 0.0
Halberd gluten + Halberd starch+ ws 2.3 ± 0.1 Halberd flour 2.7 ± 0.1
1 water-solubles from Bakers flour.
Starch and gluten fractions were then exchanged between the Bakers flour and the samples of Hartog and Halberd. The water soluble fraction for all reconstitutions was obtained from the Bakers flour and was added at a constant amount. Starch was added at a constant amount and gluten was adjusted for
140 each sample to give a total protein of 10.0% (13.5%m.b.). This was a similar protein content to the optimum found for both the Hartog and Halberd flour samples in Section 4.5.
Each combination of starch and gluten components was tested for baking absorption and dough mixing time. Gluten source did not affect the water absorption of flours however the Hartog starch required three percent more water addition for each gluten treatment. This must have been due to the high maltose value of this sample. Mixing requirements were 4.0 min. for each of the Bakers and Hartog gluten and 3.5 min. for the Halberd sample.
Protein content and maltose values for the reconstituted flours were also measured (Table 4.16), these can be compared to those for the whole flours presented in Table 4.12.
Table 4.16 Protein content and maltose values for selected reconstituted flours.
Protein Maltose Content Value Sample (%) 13.5 m.b. (mg g-1)
Bakers gluten+ Bakers starch + 1ws (10% sample) 10.3 2.4 Hartog gluten+ Hartog starch + 1ws 10.2 2.9 Halberd gluten+ Halberd starch + 1ws 10.1 2.5
All combinations of starch and gluten were then baked in
141 duplicate. A two way analysis of variance was used to identify the bread quality parameters affected by the exchange. A summary of these results follows.
Bread Area: No significant difference in scores occurred, although Halberd gluten appeared to give slightly larger bread areas. This may be the result of this cultivars weaker protein strength.
Bread Shape: Samples prepared with Halberd gluten had significantly lower scores for bread shape than the other samples (P < 0.05). The shape of Halberd samples tended to be oval which is associated with less resistance to sheeting, in this case resulting from weaker protein.
Bread Smoothness and Cracks: There were no significant differences between samples.
Crust Colour: Samples prepared with either Hartog starch or
Hartog gluten had lower scores than the other samples (P < 0.05). However all reconstituted samples had pale crusts and it is difficult to interpret this result.
Blisters: No significant differences observed.
Ability to Roll and Fold: Hartog starch resulted in
significantly higher rolling and folding scores (P < 0.01). All loaves baked with Hartog starch were softer and more flexible. This characteristic was also observed for the
142 Hartog flour sample.
Quality of Separation: All breads pocketed without any problems.
Crumb Texture: There were no significant differences between samples.
Crumb Appearance: Samples prepared from Bakers gluten gave significantly lower scores than for samples prepared from either Halberd or Hartog gluten (P < 0.05). The crumb of the samples prepared with Bakers gluten tended to be flat.
Evenness of Layers: No significant differences.
Tearing Quality: No significant differences.
Second Day Ability to Roll and Fold: The average score for samples baked with Hartog starch was 16.7 ± 0.5, whilst for
Halberd and the Bakers starch it was 14.6 ± 0.5 and 14.4 ±
0.5 respectively. This improved keeping quality associated with the Hartog starch was also observed for bread baked from
Hartog flour.
Second Day Tearing Score: No significant differences.
Total Score: The average total score for bread baked from the
samples containing Hartog starch was significantly higher
than for the other samples (P < 0.05). The higher scores due
143 to the Hartog starch were achieved for each gluten treatment (Table 4.17). This was due to the bread softness associated with this starch on both the first and second days scoring. The Hartog flour achieved a higher total score than either the Bakers or Halberd samples. This was largely due to the extra softness and flexibility of loaves made from this flour
(Table 4.17).
Moisture content: Hartog starch was associated with lower bread moisture, although the differences were small (P <
0.05). This was despite the extra baking absorption required for samples with this starch.
Table 4.17 Total Arabic bread scores for samples reconstituted with combinations of starch and gluten from the Bakers, Hartog and Halberd flour samples.
Starch source Bakers Halberd Hartog
Gluten source
Bakers 76.0 75.7 79.1 a78.9 Halberd 77.6 77.7 79.5 b77.5 Hartog 75.4 76.8 79.5 c82.5 L.S.D (0.05=5.2)
aBakers whole flour, bHalberd whole flour, cHartog whole flour
In this trial the differences between the reconstituted samples were not large, this was similar to the magnitude of the differences between the original flour samples. However a
144 consistent and significant difference was found for the Hartog flour and this was identified as being due to the starch component. This difference in bread quality due to the starch contrasts to the observations made for pan bread where differences in loaf volume are related to the gluten fraction (MacRitchie, 1978). Perhaps studies on pan bread have masked the effect of starch on bread quality by placing their major emphasis on loaf volume.
The Hartog starch had a higher level of starch damage than the other samples and whilst this must be considered as a possible explanation, starch damage levels for Hartog samples used in Section 4.5 or by Qarooni (1988a) did not have such high levels of starch damage and yet they still displayed superior keeping qualities. Another feature of the Hartog starch was its higher protein content than the other starch samples. This observation has been made with larger ranges of starch samples (D. Tomlinson, pers. comm.). Further work in this area would include the characterization of the starch samples with methods such as the Rapid Viscoanalyser, Viscograph, particle size analysis and differential scanning calorimetry (DSC). It may also be useful to follow the starch retrogradation of bread made from these samples with DSC. Further more a range of Hartog samples must be studied to ensure that this observation has a genetic origin.
145 5 CONCLUSIONS
5.1 A large proportion of Australia's wheat crop is exported to countries in the Middle East that produce Arabic bread as a major end use of the wheat. This represents significant export earnings for Australia. Therefore it is important for the Australian wheat industry to understand the factors affecting Arabic bread quality.
5.2 There has been a significant increase in the consumption of Arabic bread in Australia over the past five years. In 1989, approximately 2.3 million dollars worth of flour was sold for the production of Arabic bread in Australia. Therefore it is also of value to the Australian milling and baking industry to have an understanding of this product.
5.3 A new scoring system for the evaluation of Arabic bread quality was developed. This system provided a comparable assessment to that of Qarooni et al (1987), however it was simpler and easier to use. The proposed system is suitable for research as it provides a repeatable evaluation of bread quality and a comprehensive record of bread quality parameters. It is also suitable for quality control programmes in commercial production.
5.4 Water activity measurements indicate that Arabic bread is susceptible to spoilage by common bread moulds.
146 5.5 Moisture content of Arabic bread was affected by dough thickness and baking time and temperature conditions. Thicker doughs and higher baking temperatures for shorter times resulted in higher bread moisture.
5.6 Dough thickness and baking conditions were found to affect bread quality. These differences may be due to the following factors: moisture content, level of starch gelatinization, or differences in crumb cell structure. study of the rate of starch retrogradation of these samples may help to identify the cause of the observed differences. 5.7 Thinner doughs baked at higher temperatures for shorter times produced the best baking scores. These breads tended to be softer and more flexible when scored both two hours and 24 hours after baking. In general breads baked from doughs sheeted to less than 3mm (measured immediately after sheeting), required baking temperatures higher than 500°C, whilst doughs which are thicker than this benefited from temperatures below 5oo·c.
5.8 A new test baking method was developed. This was based on the method of Qarooni et al. (1987), with the incorporation of the improvement of bread quality using thinner doughs baked at higher temperatures. When compared to the method of Qarooni et al. (1987), the proposed method produced breads with higher overall scores and provided better differentiation between the flour samples tested.
5.9 Comparison of the new test baking method with commercial
147 production showed this method has commercial relevance and could be used to predict the performance of flours for commercial production.
5.10 The upper surface of the top layer of Arabic bread consists of a densely packed layer of ungelatinized starch, this was defined as the crust. The thickness of this layer varies with dough thickness and baking conditions. Thicker doughs resulted in thicker crusts, and higher baking temperatures resulted in thinner crusts.
5.11 The crumb component of the upper layer of Arabic bread consists of an open cell structure supported by starch which is mostly gelatinized. Samples baked at 600°C for 21sec
appeared to have less gelatinized starch than samples baked at 4oo·c for 90sec. The size of the crumb cells increased away from the crust, as a result thicker breads have a higher
proportion of larger cells than breads baked from thinner
doughs.
5.12 Breads baked at 600°C for 21sec had cells near the crust
which had a high proportion of ungelatinized starch on their
upper surface.
5.13 Observations from light and electron microscopy provided
complimentry evidence, while observation of freeze fractured
surfaces with an electron microscope allowed greater
discrimination of the level of starch gelatinization, and a
clearer view of bread microstructure.
148 5.14 A detailed description of the pocketing process was provided which incorporated the information on bread microstructure and starch gelatinization.
5.15 Flour quality is an important determinant of Arabic bread quality, however the commonly used tests of flour quality are more suited to the description of flour for the production of pan bread than Arabic bread.
5.16 For six wheat cultivars there was a parabolic relationship between bread score and protein content. For each cultivar there was a protein optimum above and below which bread quality decreased. Samples with protein contents below the optimum, had similar faults for all cultivars and samples with protein contents above the optimum had similar bread faults for all cultivars.
5.18 Optimum Arabic bread score and the protein content at which this occurred varied between cultivars.
5.19 Hard wheats (PSI ~ 20) were more suited to the production of Arabic bread than soft wheats.
5.20 Of the hard grained wheat cultivars, both Hartog and Banks at lower protein levels were more suited than Halberd or Cook to the production of Arabic bread. Amongst the hard wheats, over strength and shortness of doughs appear to be the major limiting factors for the production of quality Arabic bread.
149 5.21 The relationship between protein content and Arabic bread score for 49 samples was best described by a quadratic equation, however this accounted for only 38% of the population variance. A linear relationship between protein content and pan bread score accounted for 64% of observed variation.
5.22 Using the prediction equation of Qarooni et al (1987), a significant relationship between predicted and actual baking scores was found (P < 0.01). However the error associated with this prediction indicated that it would not be useful for the prediction of baking quality of flour samples. No useful prediction equations were generated by the present study.
5.23 Ranges for a number of wheat and flour quality parameters were defined for the assessment of samples for their suitability to the production of Arabic bread (Table 4.11). Within these ranges it is necessary to test bake in order to determine the real potential of samples for the production of Arabic bread. outside these ranges the baking potential of samples is considered severely limited.
In general the test ranges support the conclusions of other studies for hard wheats and flour of medium protein content and moderate protein strength for the production of Arabic bread. The parameters set by the present study and the advice to test bake, provide a more reliable basis for flour assessment than previously published.
150 5.24 Flour extracted with chloroform was successfully reconstituted with the extracted lipid, for three flour samples.
5.25 Flour lipid was shown to play an important role in the baking of Arabic bread. It was proposed that the most important role was for the stabilization of the cell structure during baking. This was similar to that described for pan bread, however the role of lipid may be more important for Arabic bread due to the high baking temperature which results in rapid cell expansion.
5.26 When flour lipid was separated into nonpolar and polar lipid fractions, both were found to restore the baking properties of defatted flour.
5.27 When soy oil was added to flour defatted with chloroform, it did not significantly improve the baking quality of the flour.
5.28 Neither wheat lipid or soy oil added to whole flour, at 0.5% or 1.0% of flour weight, significantly improved bread quality.
5.29 Exchange of chloroform extracted lipids between three defatted flours did not account for the difference in baking potential between these flours.
151 5.30 It was necessary to include the water-soluble fraction to achieve successful reconstitution after fractionation into starch, gluten and water-solubles. This fraction appeared to be important for yeast activity and dough development, which was consistent with the results of Hoseney et al. (1989).
5.31 When the gluten content was manipulated to produce reconstituted flours of different protein contents, the baking results showed similar trends to those observed for the whole flours. This confirmed that the method of fractionation and reconstitution employed was effective.
5.32 Exchange of gluten and starch between three flours found that the starch component of the cultivar Hartog accounted
for the superior bread quality associated with flour of this cultivar (within an appropriate protein range). This result indicates that the choice of wheat cultivar can be used to
achieve greater keeping quality which is an important aspect
of Arabic bread quality. Further study is required to confirm
this result and to elucidate the mechanism.
152 6 APPENDICES
APPENDIX 1
Questionnaire sent to Australian flour mills.
QUESTION 1
List the quantity of flour supplied by your mill to individual bakeries for the production of Arabic bread during the financial year ending June, 1988.
Bakery Registered name city [Quantity of flour I I of bakery I supplied (tonnes) 1
2
3
4
5
6
COMMENTS:
QUESTION 2
What were the approximate total tonnages of flour supplied for the production of Arabic bread in the following financial years ending June '87, June '86 and June '84? These figures will be used to determine whether or not the production of Arabic bread is constant or changing.
Financial year Total flour supplied for the ending production of Arabic bread (Tonnes)
June 1987
June 1986
June 1984
153 Appendix 2
Crumb Colour
A reference for crumb colour was made using bread samples prepared with flour of different colour grades. A flour with an initial colour grade of -0.6 was mixed with increasing quantities of pollard to produces samples with the following colour grades: 0.8, 2.0, 3.2 and 5.2. Each sample was baked in triplicate and Minolta Colour Meter readings taken of the crumb in the center of the upper layer. Of the six measurements made, the "Y" value gave the most useful relationship (Figure A.1).
Visual judgement of the crumb colour found that it lost its appeal at a flour colour grade above 3.2.
This method of evaluation of the crumb colour was very different to that of Qarooni et al (1987). They established a standard curve for crumb colour by baking the breads made from the same flour for different times and measuring the crumb colour with a Hunter Lab Colour Difference Meter. The result was that no significant correlation between crumb colour and flour colour was established when 33 flour samples with colour grades ranging from -0.6 to 7.1 were measured. On this basis it is doubtful that the crumb colour measurements were of value.
Objective measurement of crumb colour was not used for the
154 bread scoring system developed in this study. This was because in all instances flour colour grades of the flour samples used were below 3.2 . It was considered that whilst it is important to have a reference as established here, crumb colour could be effectively assessed by a trained bread scorer.
crust Colour
An objective measurement of crust colour was made as a reference. Bread prepared from a commercial bakers flour was baked for different times at 400°C to produce a range of crust colour. Measurements with the Minolta Colour Meter were made of the upper crust of these samples. The samples were baked in triplicate and two measurrements were made for each loaf. Of the prameters measured by the Minolta Colour Meter,"x" gave the most useful relationship (Figure
A.2). This is a similar approach to that used by Qarooni et al (1987), except that they used a Hunter Lab Colour Difference Meter for objective measurement.
A golden brown colour is considered the optimum crust colour, although this may vary with individual consumer preference. Optimum colour occurred in the range of x= 0.360 to 0.374. Objective measurement of crust colour was not used to score breads for this study because it was found that a trained scorer was able to discriminate between poor, satisfactory and good crust colour sufficiently for the scoring purposes.
155 Crumb Minolta Y value 60.------~
59
58
57 56
55
54
53
52
51 so---~---~---~---~--~---~--"'---' -1 0 1 2 3 4 5 6 Flour colour grade
Figure A.1 Flour colour grade versus Arabic bread crumb colour (Y value, Minolta Colour Meter).
Crust colour Minolta x value 0.39 ~------,
0.385 >--
0.38 ~
0.375,..
0.37 0.365
0.34 -----~1 ----~1 ----~_Ll_____ .L__l ___ -----" 75 80 85 90 95 100 Baking time (sec)
Figure A.2 Baking time versus Arabic bread crust colour (x value, Minolta colour meter).
156 APPENDIX 3 Analytical Data of Wheat and Flour Samples (Section 4.5) Farino graph Variety Flour Particle Maltose Water Dev. Extenso- Arabic Protein Size Abs. Time -grap2 Area Bread (%) Index (mg) (%) (min) (cm) Score Rosella 13.0 30 104 56.8 4.2 162 61 12.3 30 90 56.1 3.6 145 65 11.4 28 106 56.6 4.2 141 73 10.1 29 116 55.3 2.7 94 73 8.9 29 121 54.4 3.1 65 68 8.0 21 130 56.0 1. 6 55 67 7.1 26 121 51. 7 1. 3 69 54 Hartog 11.8 13 237 62.5 5.2 169 65 10.8 13 241 64.7 4.8 132 71 9.8 13 254 63.6 3.9 107 81 9.1 13 243 62.8 1. 9 96 80 8.4 13 251 62.4 1. 5 89 74 Egret 13.4 23 116 59.0 4.2 75 65 11. 6 27 119 56.6 3.9 98 72 10.5 27 130 56.9 2.9 66 68 9.7 28 135 56.2 2.8 63 66 8.5 28 111 55.9 1.6 55 46 7.8 32 126 55.2 1. 5 51 40 Banks 12.7 12 171 62.1 4.0 107 65 11. 7 14 195 63.l 4.6 124 77 10.7 15 198 62.4 4.5 109 79 9.5 13 192 59.7 3.8 103 80 9.2 11 210 58.4 2.7 97 78 7.9 22 143 55.5 2.9 64 69 Halberd 13. 3 16 201 62.8 4.0 72 67 11. 9 17 207 60.7 5.3 111 67 11.0 16 261 62.3 4.0 48 76 9.8 16 237 60.5 3.5 67 77 9.7 13 251 63.2 3.5 56 75 7.8 14 267 60.2 1.5 58 69 Cook 13.5 16 176 64.5 7.0 134 63 12.3 13 261 61. 9 8.2 158 62 11. 6 15 198 63.6 4.0 92 74 10.5 15 121 61.4 5.5 121 74 9.1 15 188 59.0 2.0 115 74 7.7 15 198 59.2 1. 7 92 65 Kulin 10.7 28 135 57.2 3.0 94 76 9.6 27 135 57.5 3.5 69 74 8.0 26 161 57.4 2.0 70 66 Minto 12.1 15 164 61.1 5.8 129 65 11.1 15 204 61.4 4.2 110 69 10.7 19 154 59.5 4.0 85 74 9.3 17 171 58.5 3.0 89 74 Osprey 12.7 14 156 61.4 5.0 119 69 12.0 11 201 64.4 3.8 80 77 11. 8 15 201 64.1 4.5 94 71 10.4 14 185 63.5 3.5 84 76 9.8 13 185 61. 9 3.5 74 76 9.2 12 218 61. 8 3.2 76 77
157 APPENDIX 4
Papers generated from this study as of November 1990.
Quail, K.J., McMaster, G.J., Tomlinson, D.J. and Wootton, M. Effect of baking temperature/time conditions and dough thickness on Arabic bread quality. J. Sci. Food Agric. 53 (in press).
Quail, K.J., McMaster, G.J. and Wootton, M. Flour quality tests for selected wheat cultivars and their relationship to Arabic bread quality. J. Sci. Food Agric. 53 (in press).
Quail K.J., McMaster, G.J. and Wootton, M. (submitted September, 1990). The role of flour lipid in the production of Arabic bread. J. Cereal Sci.
Quail, K.J., McMaster, G.J. and Wootton, M. (submitted October, 1990). Flat bread production. Food Technology Australia.
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