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1985 Modification of Rice Flour and Its Potential Use in the Food Industry. Samir Sideek Alhusaini Louisiana State University and Agricultural & Mechanical College
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University Microfilms International 300 N. Zeeb Road Ann Arbor, Ml 48106
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Alhusaini, Samir Sideek
MODIFICATION OF RICE FLOUR AND ITS POTENTIAL USE IN THE FOOD INDUSTRY
The Louisiana State University and Agricultural and Mechanical Col. Ph.D. 1985
University Microfilms International300 N. Zeeb Road, Ann Arbor, Ml 48106
Copyright 1985 by Alhusaini, Samir Sideek All Rights Reserved
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University Microfilms International
MODIFICATION OF RICE FLOUR AND ITS POTENTIAL USE IN THE FOOD INDUSTRY
A Dissertation
Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requriements for the degree of Doctor of Philosophy
in
The Department of Food Science
by
Samir Sideek Alhusaini B.S. University of Baghdad, 1972 M.S. Colorado State University, 1979 May 1985 © 1985
SAMIR SIDEEK ALHUSAINI
Alt Rights Reserved ACKNCWLEBGEMEKTS
Hie author wishes to extend his sincere appreciation and thanks
to Dr. Auttis Mullins, his major advisor and head of Food Science
Department for his advice, assistance and support throughout this
study.
Deep appreciation is extended to Dr. Darrell Gerdes, Dr, Robert
Grodner, Dr. Cameron Hackney of Food Science, Dr. Charles White of
Dairy Science and Dr. Jesse Jaynes of Biochemistry for their support,
assistance and serving on my examining committee.
Very special thanks are extended to Dr. James Rutledge and Dr.
Stanley Biede, former-faculty members of the Food Science Department
and my former advisors for the support, encouragement mid advice.
Special thanks for the faculty, staff and students of the Food
Science Department for their help and friendship.
The author would like to express his deep appreciation to all the other persons who have assisted with this study.
Very special thanks for Dr. Fahri Albagdadi of Anatcmy and Fine
Structure, School of Veterinary Medicine, for his help and guidance.
Appreciation and gratitude are due to my Father, Mother and all my family in Iraq, their love and support are indispensible.
Above all, the author wishes to express his gratitude to
Intithar, his wife, for her patience, understanding and support throughout this study, this dissertation is dedicated to her. TABLE OF CONTENTS
PAGE
ACKNOWLEDGEMENTS...... ii
TABLE OF CONTENTS ...... iii
LIST OF TABLES...... V
LIST OF F I G U R E S ...... vii
ABSTRACT...... XV
INTRODUCTION...... 1
LITERATURE REVIEW ...... 3
RICE- History and Production ...... 3
Composition and Nutritional Value of rice. . . 5
RICE IN THE FOOD INDUSTRY...... 12
Parboiled R i c e ...... 12
Quick Cooking R i c e ...... 14
Gun Puffed Rice Products ...... 16
Breakfast Cereals...... 17
MODIFICATION OF STARCHES AND THEIR USE IN THE FOOD INDUSTRY...... 22
Acid Modification...... 22
Oxidized Starches...... 23
Cross-linked Starches...... 24
Starch Phosphates...... 25
Pregelatinized Starches...... 26
Starch Acetate ...... 27
RICE F L O U R ...... 29
BREAD MANUFACTURING...... 33 PROBLEMS ASSOCIATED WITH WHEAT FLOUR BREAD ...... 37 TABLE OF CONTENT (cont'd)
PAGE
MATERIALS AND METHODS...... 42
PREPARATION OF MODIFIED RICE FLOUR...... 42
Chemical Control...... 42
Chemical Treatment With Anhydrides...... 42
MOISTURE...... 43
CRUDE F A T ...... 43
ASH ...... 43
PROTEIN DETERMINATION ...... 43
COLOR DETERMINATION ...... 43
CIARITY M E A S U R E M E N T ...... 44
AMYLOGRAPH A N A L Y S I S ...... 44
Sample Preparation for the Amylograms ...... 44
Amylograph Procedure...... 44
BREAD MAKING...... 45
BREAD VOLUME...... 46
WATER ACTIVITY...... 46
TEXTURE ANALYSIS...... 46
ELECTRON MICROSCOPY OF RICE FLOUR AND B R E A D ...... 47
TASTE PANEL EVALUATION...... 47
STATISTICAL ANALYSIS...... 49
RESULTS AND DISCUSSION ...... 51
PROXIMATE COMPOSITION OF R I C E ...... 51
COLOR AND CHROMATICITY OF RICE FLOUR...... 62
CLARITY MEASUREMENTS...... 68
iv TABLE OF CONTENT (cont'd)
PAGE
AMYLOGRAPH ANALYSIS
At Neutral pH ...... 84
At Acidic p H ...... 105
BREAD MAKING ...... 110
Specific Volume...... 125
Water Activity ...... 136
Texture A n a l y s i s ...... 141
Electron Microscopy of Rice Flours and Rice Breads ...... 147
Sensory Evaluation ...... 160
SUMMARY AND CONCLUSIONS ...... 174
BIBLIOGRAPHY...... 177
VITA ...... 189
v LIST OF TABLES
Tables Page
1 Rice Bread Formula...... 45
2 Proximate analysis of unmodified and modified rice flours...... 52
3 The effect of acetic anhydride versus succinic anhydride and their concentration on ash content of the modified rice flour ...... 55
4 The effect of alkali and anhydride concentration on ash content of modified rice flour. . . . 58
5 The effect of anhydrides, alkali and their interaction on protein content of modified rice flours...... 60
6 Total color difference and total chromaticity difference of modified rice flour...... 63
7 Mean values of total color differences and total chromaticity differences for modified rice flours as influenced by the concentration of anhydrides and alkali...... 65
8 Amylograph viscosities of unmodified and modified rice flour at neutral pH ...... 101
9 Mean Value for amylograph viscosities of modified rice flours ...... 103
10 Amylograph viscosities of unmodified and modified rice flours at acidic pH ...... 107
11 Water activity (a ) and specific volume (cc/gm) of rice breads made from modified rice flours...... 137
12 The effect of anhydrides concentration and type of alkali on the specific volume of rice b r e a d ...... 139
13 The effect of anhydrides concentration on the water activity of breads made from modified rice flours ...... 140
14 Texture analysis of rice bread ...... 142
vi LIST OF TABLES (cont'd)
Tables Page
15 Mean value for shear press (pH/W) for modified rice breads as influenced by the anhydride type and their concentrations...... 144
16 Shear press values as influenced by the alkali type at different anhydrides concentrations...... 145
17 Sensory evaluation scores for bread made from modified rice flours...... 161
18 Effect of rice flour modification on the sensory characterisitcs of rice bread . . 163
19 Effect of anhydrides concentrations at different modification times on the grain score of bread crumb...... 165
20 Effect of alkali in different concentrations of the anhydries on the grain score of bread crumb ...... 167
21 Effect of alkali in different anhydrides concentrations of the total score for rice bread...... 170
vii LIST OF FIGURES
Figure Page
1 A typical compression test curve showing the utilization of the cun/e to calculate the elasticity modulus...... 48
2 Score sheet for bread evaluation ...... 50
3 Ash content of anhydride modified rice flour . . 56
4 Ash content of modified rice flours under different concentration of anhydride and alkali...... 57
5 Protein content as affected by anhydride and alkali...... 71
6 Total color differences of rice flours treated with different concentration of anhydrides using sodium carbonate and sodium h y d r o x i d e ...... 66
7 Total chromaticity differences for rice flours treated with different concentration of anhydrides using sodium carbonate and sodium hydroxide...... 67
8 Opacity of rice flour treated for 1, 6 and 18 hours with sodium hydroxide ...... 69
9 Opacity of rice flour treated for 1, 6 and 18 hours with sodium carbonate ...... 70
10 Opacity of rice flour treated for 1, 6 and 18 hours with 0.1% acetic anhydride and sodium hydroxide ...... 71
11 Opacity of rice flour treated for 1, 6, and 18 hours with 1.0% acetic anhydride and sodium hydroxide...... 72
12 Opacity of rice flour treated for 1, 6 and 18 hours with 5.0% acetic anhydride and sodium hydroxide...... 73
13 Opacity of rice flour treated for 1, 6 and 18 hours with 0.1% succinic anhydride and sodium hydroxide...... 74
viii Page
Opacity of rice flour treated for 1, 6 and 18 hours with 1.0% succinic anhydride and sodium hydroxide...... 75
Opacity of Rice flour treated for 1, 6 and 18 hours with 5.0% succinic anhydride and sodium hydroxide...... 76
Opacity of rice flour treated for 1 , 6 and 18 hours with 0.1% acetic anhydride and sodium carbonate...... 77
Opacity of rice flour treated for 1, 6 and 18 hours with 1.0% acetic anhydride and sodium carbonate...... 78
Opacity of rice flour treated for 1, 6 and 18 hours with 5.0% acetic anhydride and sodium carbonate...... 79
Opacity of Rice flour treated for 1, 6 and 18 hours with 0.1% succinic anhydride and sodium carbonate...... 80
Opacity of rice flour treated for 1, 6 and 18 hours with 1.0% acetic anhydride and sodium carbonate...... 81
Opacity of rice flour treated for 1, 6 and 18 hours with 5.0% succinic anhydride and sodium carbonate...... 82
Amylograph at pH 6 of untreated rice flour (control) ...... 85
Amylograph at pH 6 of rice flour treated for 1, 6 and 18 hours with sodium hydroxide . . 87
Amylographs at ph 6.0 of rice flour treated for 1 , 6 and 18 hours with sodium carbonate . . 88
Amylogrpahs at pH 6.0 of rice flour treated for 1, 6 and 18 hours with acetic anhydride and sodium hydroxide...... 89
Amylographs at pH 6.0 of rice flour treated for 1, 6 and 18 hours with acetic anhydride and sodium hydroxide...... 90
Amylogrpahs at pH 6.0 of rice flour treated for 1, 6 and 18 hours with acetic anhydride and sodium hydroxide...... 91
ix Page
Amylographs at pH 6.0 of rice flour treated for 1, 6 and 18 hours with 0.1% succinic anhydride and sodium hydroxide...... 92
Amylographs at pH 6.0 of rice flour treated for 1, 6 and 18 hours with 1.0% succinic anhydride and sodium hydroxide...... 93
Amylographs at pH 6.0 of rice flour treated for 1, 6 and 18 hours with 5.0% succinic anhydride and sodium hydroxide...... 94
Amylographs at pH 6.0 of rice flour treated for 1 , 6 and 18 hours with 0.1% acetic anhydride and sodium carbonate...... 95
Amylographs at pH 6.0 of rice flour treated for 1, 6 and 18 hours with 1.0% acetic anhydride and sodium carbonate...... 96
Amylograph at pH 6.0 of rice flour treated for 1, 6 and 18 hours with 5.0% acetic anhydride and sodium carbonate...... 97
Amylographs at pH 6.0 of rice flour treated for 1, 6 and 18 hours with 0.1% succinic anhydride and sodium carbonate...... 98
Amylographs at pH 6.0 of rice flour treated for 1, 6 and 18 hours with 1.0% succinic anhydride and sodium carbonate...... 99
Amylographs at pH 6.0 of rice flour treated for 1, 6 and 18 hours with 5.0% succinic anhydride and sodium carbonate...... 100
Amylograph at pH 3.5 of unmodified rice flour (control) ...... 106
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 hours with sodium hydroxide . . 111
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 hours with sodium carbonate . . 112
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 hours with 0.1% acetic anhydride and sodium hydroxide...... 113
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 hours with 1.0% acetic anhydride and sodium hydroxide...... 114
x Page
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 with 5.0% acetic anhydride and sodium hydroxide...... 115
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 hours with 0.1% succinic anhydride and sodium hydroxide...... 116
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 hours with 1.0% succinic anhydride and sodium hydroxide...... 117
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 hours with 5.0% succinic anhydride and sodium hydroxide...... 118
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 hours with 0.1% acetic anhydride and sodium carbonate...... 119
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 hours with 1.0% acetic anhydride and sodium carbonate...... 120
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 hours with 5.0% acetic anhydride and sodium carbonate...... 121
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 hours with 0.1% succinic anhydride and sodium carbonate...... 122
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 hours with 1.0% succinic anhydride and sodium carbonate...... 123
Amylographs at pH 3.5 of rice flour treated for 1, 6 and 18 hours with 5.0% succinic anhydride and sodium carbonate...... 124
Cross sections of bread made with modified rice flour...... 126 a. No modification (Control) b. Sodium hydroxide for 1 hr. c. Sodium hydroxide for 6 hr. d. Sodium hydroxide for 18 hr. e. Sodium carbonate for 1 hr. f. Sodium Carbonate for 6 hr. g. Sodium Carbonate for 18 hr.
xi Figure Page
53 Cross sections of bread made with modified rice flour...... 128
a. 0.1% acetic anhydride and sodium hydroxide for 1 hr. b. 0.1% acetic anhydride and sodium hydroxide for 6 hr. c. 0.1% acetic anhydride and sodium hydroxide for 18 hr.
d. 1.0% acetic anhydride and sodium hydroxide for 1 hr. e. 1.0% acetic anhydride and sodium hydroxide for 6 hr. f. 1.0% acetic anhydride and sodium hydroxide for 18 hr.
g. 5.0% acetic anhydride and sodium hydroxide for 1 hr. h. 5.0% acetic anhydride and sodium hydroxide for 6 hr. i. 5.0% acetic a n h y d r i d e and sodium hydroxide for 18 hr.
54 Cross sections of breads made with modified rice flour ...... 130
a. 0.1% succinic anhydride and sodium hydroxide for 1 hr. b. 0.1% succinic anhydride and sodium hydroxide for 6 hr. c. 0.1% succinic anhydride and sodium hydroxide for 18 hr.
d. 1.0% succinic anhydride and sodium hydroxide for 1 hr. e. 1.0% succinic anhydride and sodium hydroxide for 6 hr. f. 1.0% succinic anhydride and sodium hydroxide for 18 hr.
g. 5.0% succinic anhydride and sodium hydroxide for 1 hr. h. 5.0% succinic anhydride and sodium hydroxide for 6 hr. i. 5.0% succinic anhydride and sodium hydroxide for 18 hr.
xii Figure Page
55 Cross section of breads made with modified rice flour...... 132
a. 0.1% acetic anhydride and sodium carbonate for 1 hr. b. 0.1% acetic anhydride and sodium carbonate for 6 hr. c. 0.1% acetic anhydride and sodium carbonate for 18 hr.
d. 1.0% acetic anhydride and sodium carbonate for 1 hr. e. 1.0% acetic anhydride and sodium carbonate for 6 hr. f. 1.0% acetic anhydride and sodium carbonate for 18 hr.
g. 5.0% acetic anhydride and sodium carbonate for 1 hr. h. 5.0% acetic anhydride and sodium carbonate for 6 hr. i. 5.0% acetic anhydride and sodium carbonate for 18 hr.
56 Cross sections of breads made with modified rice flours...... 134
a. 0.1% succinic anhydride and sodium carbonate for 1 hr. b. 0.1% succinic anhydride and sodium carbonate for 6 hr. c. 0.1% succinic anhydride and sodium carbonate for 18 hr.
d. 1.0% succinic anhydride and sodium carbonate for 1 hr. e. 1.0% succinic anhydride and sodium carbonate for 6 hr. f. 1.0% succinic anhydride and sodium carbonate for 18 hr.
g. 5.0% succinic anhydride and sodium carbonate for 1 hr. h. 5.0% succinic anhydride and sodium carbonate for 6 hr. i. 5.0% succinic anhydride and sodium carbonate for 18 hr.
xiii Page
The effect of sodium carbonate versus sodium hydroxide at different anhydride concentrations on the force required to shear the bread slices...... 146
Scanning electron micrographs of a) unmodified rice flour; b) Modified rice flour with 1.0% acetic anhydride in sodium hydroxide for 6 hr; c) modified rice flours with 1.0% succinic anhydride in sodium hydroxide for 6 h r ...... 149
Scanning electron micrograhps of a) rice bread; wheat bread; c) rice bread made from rice flour modified for 6 hr. with sodium hydroxide; d) rice bread made from rice flour flour modified for 6 hr. with sodium carbonate ...... 151
Rice bread made from rice flour modified for 6 hr. with a) 1.0% acetic anhydride and sodium hydroxide; b) 5.0% acetic anhydride and sodium hydroxide...... 154
Rice bread made from rice flour modified for 6 hr. with a) 0.1% acetic anhydride and sodium hydroxide; b) 0.1% succinic anhydride and sodium hydroxide; c) 0.1% succinic anhydride and sodium carbonate; d) 0.1% acetic anhydride and sodium carbonate .... 156
Rice bread made from rice flour modified for 6 hr. with a) 1.0% succinic anhydride and sodium hydroxide; b) 1.0% succinic anhydride and sodium carbonate; c) 5.0% succinic anhydride and sodium carbonate ...... 159
The effect of anhydride modification of rice flour bread grain scores...... 164
The effect of alkali in different concentrations of anhydride on the bread grain scores. . . . 166
The effect of anhydride concentrations at diffierent modification times on the bread crumb grain scores...... 168
The effect of alkali at different concentrations of anhydrides on the total score of rice bread...... 171
xiv ABSTRACT
Rice flour was modified with either 0.1, 1.0 and 5.0% acetic or
succinic anhydride for 1, 6 and 18 hr under basic conditions. The pH was maintained above 7.0 using either sodium hydroxide or sodium carbonate. The results showed that modified rice flours had lower
fat content as compared with the unmodified rice flour (control) .
The type of anhydride significantly influenced the fat content of rice flour. Ash content of rice flour increased significantly due to the anhydride concentrations and alkali type. Significant differences were also found in the protein content of modified rice flours due to the use of anhydride and alkali types.
Different concentrations of anhydrides alkali types resulted in an increase in the total color and chromaticity differences from the control. In general, solutions of modified rice flour had better clarity than that of the control.
Flour slurries behavior under neutral and acidic conditions was altered by modification with the anhydrides. Significant differences were found among the peak viscosities at 95°C, viscosities after holding at 95°C for 30 minutes and the setback viscosity of modified rice flours.
Flour modification resulted in production of rice bread with better quality and acceptability when compared with bread produced with unmodified rice flour. Breads with larger volume, softer crumb and better taste were produced from modified rice flour. Although seme modifications resulted in inferior quality breads.
x v Electron micrographs of rice flour and rice breads revealed that modification with anhydrides influenced their ultrastructure noticably in canparison with that of unmodified rice flour and bread.
XVI Chapter I
nmoxicTTCN
Rice has been one of the roost commonly used grains since
ancient times. It is the staple food for the greatest number of
people, with over half the world's population eating rice as the main
article of diet. Rice is produced in different parts of the world,
but primarily in Asia. It is also produced in the United States
primarily in the south, southeastern states and California. Medium
and long grain rice are grown in the southern states, while short
grain rice is grown in California. Rice is an important commodity in
the state of Louisiana.
In the more densely populated areas of the tropics, in addition
to its use as a source of energy, rice is also used as a main source
of dietary protein. Starch comprises about 90% of the total dry
substance of polished rice, protein about 8%, lipids 0.5% and ash
about 0.5%.
Rice is high in caloric value, N-free extract and niacin as
compared with other cereals. Rice has a fairly good balance of
essential amino acid and is fairly low in glutamic and some other non-essential amino acids. Rice contains high amounts of lysine in
canparison to other cereals, although lysine is still the first
limiting essential amino acid in rice. When mixed with diets based on potatoes, com, pinto bean and cottonseed meal, rice improved the nutritional quality of those diets. The favorable amino acid balance
1 2
of rice is shown by the fact that rice can be supplemented to bring the lysine content to an optimum level at lower cost than for wheat, com, millet or sorgum.
Rice protein lacks gluten, the main fraction in wheat protein.
Gluten is the protein fraction which is important for the utilization of wheat flour in different food products, especially bakery products. Gluten is also mainly responsible for the functionality of wheat flour in such food products. The lack of gluten in rice makes rice flours have poor functionality and of limited use in the food industry. The absence of gluten, low levels of protein, sodium, fat and fiber and the high amount of easily digested carbohydrates makes rice desirable for special diets. Patients with wheat or gluten allergies, hypertension, nephritis, urimic or digestive difficulties could benefit if good quality rice products such as bread, were made available, especially since it would provide another choice in their diets.
This study investigated the possible increase of the functional properties of rice flour through chemical modification to increase its utilization in the food industry, to provide new products for those who require special diets free from wheat and related cereals and to produce products such as bread for countries which mainly produce rice and have to import wheat for bread manufacturing. Chapter II
LITERATURE REVIEW
Rice - History and Production
Oryza sativa L. is the the major species of rice cultivated.
There are over ten thousand varieties of 0. sativa which are
classified into three subspecies: Indica long grains, Japonica thick
and short grains and Javonica broad thick grains. Within each of
these subgroups there exists waxy and non waxy types. The waxy types
have different cooking characteristics compared to the cannon non
waxy types of rice (Lu and Chang, 1980).
Rice is generally considered a semi-aquatic plant, although it
caii survive in the tropics or the subtropics. Twenty valid species
of rice are known to man. Oryza sativa L. and Oryza glaberrimasteud
are the most popular species and can be grown under different
conditions, ranging from lands flooded in deep water to drylands (Lu
and Chang, 1980). Today, more than 100 countries around the world
produce rice. The area of production extends from 50° north latitude
to 35° south latitude (Lu and Chang, 1980).
Rice varieties mature in different lengths of time, ranging fran
3 to 11 months. In some areas double or triple cropping is being
practiced, therefore, it is difficult to estimate precisely the total
rice hectarage. The world rice hectarage increased from 108.8 million hectare in 1953 to 144.7 million hectare in 1978. However,
this increase in acreage has not been uniform throughout the world
(Lu and Chang, 1980).
3 4
The Asian countries share of the world rice hectarage is about
90% followed by 4.53% for South America, 3.29% in Africa, 1.4% in
North America, 0.70% in Europe and 0.6% in Oceania (Lu and Chang,
1980). In 1978 the world's rice production was about 377 million
metric tons (Palacpac, 1977; Palacpac, 1978; USDA, 1979).
In 1975 the per capita consumption of rice was about 94.7 kg of milled rice for Asia, 33.54 kg for South America, 20.13 kg for
Africa, 15.5 kg for Oceania and 8.77 kg for North and Central
America. The world's average per capita consumption was 58.42 kg.
The largest per capita consumption was 246.46 kg by the South
Vietnamese followed by the Thais with 212.54 kg per capita. This is
compared with 6.39 kg per capita consumption by the United States
(USDA, 1976). The increase in world population between 1960 and 1976 was 30.27%, while the consumption of rice increased at a rate of
42.03% for the same period of time. People are now eating more rice and the increase in consumption coincides with an increase in income.
As incomes increased, a large sector shifted consumption behavior
toward finer foods such as rice. For example, in West Africa the demand for rice has surpassed maize, yams and cassava (Lu and Chang,
1980).
Commercial rice production in the United States started in 1685
in South Carolina. Production later spread into North Carolina,
Georgia, Alabama, Mississippi and Florida (Walker, 1960). After the
Civil War the southern states became the important rice producing
states in the United States with a rapid increase in rice acreage along the Mississippi River in Louisiana. At the beginning of the 5
20th Century rice growing extended to Texas and Arkansas then to
California.
Crop acreage increased irregularly in the United States and
reached a maximum in 1954, when more than one million hectare were
planted in rice. In 1954 rice acreage was put under government
control. The United States production increased steadily and in 1962
the export of U.S. rice exceeded one million metric tons. Between
1972 and 1975 the U.S. led the world with an average export of 1.78 million metric tons of milled rice, followed by China and Thailand with 1.51 and 1.14 million metric tons, respectively. During this
period the world production stood at 7.44 million metric tons (Lu and
Chang, 1980). In recent years the world production of rice has
increased by more than 50% due to many factors, primarily the use of high yield varieties and associated technologies.
The most common classification of rice is based on grain size.
Rice is classified as long, medium and short grain varieties. Long grain rice is produced in the southern states while the short grain production area is confined to California. Medium grain rice is grown in all rice producing areas.
Besides grain size, other characteristics used to classify rice are: 1) waxy and non-waxy and 2) glutinous and non-glutinous.
Composition and Nutritional Value of Rice
After harvesting, rough rice is dried and milled to remove the hull. The product of the dehulling process is known as brown rice.
Brown rice still contains the bran layer. White rice, which is more common, is produced by further milling of the brown rice. 6
Protein values (N X 5.95) have been reported to range from 5% to more than 13% for milled rice and slightly higher for brown rice.
Rice protein content is predominantly less than 10% for milled rice and brown rice. Protein content is influenced by varietal differences, planting date, fertilization, yield and environmental conditions (Saunders and Betschart, 1979). Rice protein is the major protein source for tropical Asians for whom rice contributes frcm 30 to 80% of calories and protein. White rice protein consists of about
3 to 5% albumin, 8 to 10% globulin, more than 80% glutelin and about
5% prolamins (Juliano, 1972a).
Quantitatively, rice is low in protein. However, rice protein has one of the highest nutritive values among cereal proteins due to its high lysine content when compared with other cereal proteins.
Despite the fact that lysine is available in higher quantities than other cereals, it is still the number one limiting amino acid in rice followed by threonine (Pecora and Hundley, 1951; Rosenberg, 1959).
Rice protein content of the essential amino acids is higher as compared to other cereals. However, it is low in glutamic acid and seme other non-essential amino acids (Houston and Kohler, 1970).
Brown rice has higher amounts of lysine than white rice due to the high lysine albumin which is located mainly in the outer layer of the kernel especially the aleurone layer (Tarnura and Kenmochi, 1963;
Baldi et al., 1976). The fraction of protein that has the highest amount of lysine is albumin followed by glutelin, globulin and prolamin (Tarnura et al., 1952; Lindner et al., 1961). 7
The addition of rice and rice by-products improves diets which
have been based on potatoes, c o m meal, pinto beans and cottonseed
meal (Kik, 1965) . Due to the high amount of lysine in rice as
compared to other cereals, the cost of supplementation of rice with
lysine to an optimum level is lower (Howe et al., 1967).
One of the popular methods for measuring the nutritive value of
protein is the protein efficiency ratio (PER). Egg protein has a
maximum of 3.5 to 4.0 PER. Egg protein is used as a standard to
evaluate other proteins. For rice the PER values range from 1.38 to
2.56 (Juliano, 1972a,b). The variations in the PER values are due to
varietal differences, protein level and experimental conditions. It
had been found that the PER values for Bluebonnet and Colusa
varieties are 2 and 1.9, respectively (Kennedy, 1980). Protein with
a PER of 2 or more is considered to be of good nutritional quality
and produce good growth in lab animals. The biological value of
brown rice and milled rice ranges from 67 to 89 and 61 to 81,
respectively (Sure and House, 1948; Kik, 1957). Fractions of the
protein have different biological values and depend upon the level of
the essential amino acids in each fraction (Lozsa and Koller, 1954).
Globulin and albumin have the highest biological value while prolamin has the lowest biological value.
The major component of rice is starch. Milled rice can have up
to 90% starch on a dry weight basis. Rice starch is comprised of
amylose (linear fraction) and amylopectin (branched fraction). The major fraction is amylopectin and is the only fraction in waxy rice.
Amylose content of non-waxy rice ranges from 8 to 37% of the starch 8
(Juliano et al., 1964; Juliano, 1970). Amylose ranges from 1 to 2% in waxy type rice.
Amylose and amylopectin gelatinization temperatures range from
55-79°C depending upon the cultivar and the environmental conditions during plant growth (Vidal and Juliano, 1967). Gelatinization temperatures may vary for different sairples of the same cultivar by be as much of 10°C. Gelatinization temperature is used to classify different rice varieties into low (<69°C), intermediate (70 to 74°C) and high gelatinization temperatures (>74°C) (Beachell, 1967).
Rices with different gelatinization temperatures differ in their water-absorption pattern. Starches with low gelatinization temperatures start to absorb water at lower temperatures than those with high gelatinization temperatures (Juliano et al., 1969). Water absorption of non-waxy starches continues even above its gelatinization temperature. In waxy starches the maximum water absorption is near the gelatinization temperature (Juliano et al.,
1969). Differences in gelatinization temperatures may be reflected in soaking time differences of the white rice (Juliano et al., 1965;
Juliano et al., 1969). The higher the gelatinization temperature the longer the cooking time. The starch with a lower gelatinization temperature tends to absorb water and swell at a lower temperature during cooking as compared to starches of higher gelatinization temperatures (Nagato and Kishi, 1966). Gelatinization temperatures of rice starches are usually higher than that of other common starches, thus rice starch requires higher cooking temperatures to effect a viscous paste. 9
The water absorption capacity of the starch molecules increases
with the increase in amylose content of the starch due to the greater
capacity of amylose to hydrogen bond. The maximum viscosity or peak
viscosity of waxy rices occurs at a lower temperature than that of
non-waxy rices.
Non-waxy rice is classified according to its amylose content as
low (10 to 20%), intermediate (20 to 25%) and high (25 to 33%)
amylose (Juliano, 1972a,b; Juliano et al., 1974). The most important
factor in determining the eating quality of cooked rice and rice cake
is the amylose-amylopectin ratio (Juliano et al., 1965; Juliano,
1973; Perdon and Juliano, 1975). Ambient temperatures during grain
development affect the grain amylose content especially in low
amylose rices (Nikuni et al., 1969; Suzuki and Murayama 1967;
Resurreccion et al., 1977).
The viscosity of high amylose rice usually drops very little
during cooking at high temperatures. The viscosity increases very
little upon cooling to 50°C.
A rice starch amylograph typical of most non-waxy cereals shows
a moderate pasting peak with a moderate decrease in viscosity when held at high temperature. The decrease in viscosity upon holding at high temperature is due to limited fragmentation and solubilization of the stable swollen granules. This is followed by an increase in viscosity upon cooling which is due to retrogradation and congelation of the amylose fraction (Schoch, 1967) . High amylose rice gives a
fluffy dry cooked rice while low amylose rice generally results in a
sticky cooked rice. 10
Other carbohydrates are present in rice in small amounts. The
sugar content of rice in the form of glucose and reducing sugars is
about 0.83 to 1.36% and 0.37 to 0.53% for brown rice and milled rice,
respectively (Juliano, 1972b). The main non-reducing and reducing
sugars are sucrose and glucose, respectively. The presence of
fructose, maltose, galactose, raffinose and other oligosaccharides
has been reported (Juliano, 1966).
Phytin is an important constituent of the outer layer of the
cereal grain. About 40% of the phosphorus content in milled rice and
80% of the phosphorus in brown rice is phytate phosphorus (McCall et al., 1953). Reported phytin phosphorus contents are: brown rice-
0.21 to 0.28%, milled rice - 0.04 to 0.06% and bran polish - 2.0 to
2.6% (Juliano, 1972b; Hayakawa, 1977).
Hemicellulose along with cellulose constitute dietary fiber and are highest in the rice bran and polish. It has been reported that brown rice contains 1.4 to 2.1% pentosans, while milled rice contains
0.6 to 1.1% compared to 8.6 to 10.9% in bran and 3.2 to 6% in polish
(Leonzio, 1967) . The distribution of pentosans is 43% in bran, 75%
in polish cind 42% in milled rice.
The distribution of cellulose in brown rice is 62% in bran and
27% in milled rice (Leonzio, 1967) . The high cellulose content in bran is constituent with the thick cell walls of the pericarp, the seed coat and the aleurone layer.
Fiber content of rices are 0.9% - brown, 0.3% - white and 0.2%
for parboiled (Watt and Merrill, 1963) . The fiber content of the outer layers of the rice kernels was reported as high as 6 to 7 times 11
as concentrated as in the original rice (Houston, 1967).
Rice contains very low amounts of fat. It has been reported
that total fat was 0.65% with a range of 0.19 to 2.73% (Simpson
et al., 1965). Fatty acids consisted of about 20% polyunsaturated
acids, linoleic and linolenic (Ressurreccion and Juliano, 1975). The
highest concentration of fat is in the outer layers and the lowest in
the central portion (Casas et al., 1963; Houston et al., 1964).
Ash content of rice ranged from 0.26 to 1.95% on a dry weight
basis (Simpson et al., 1965). Here again, ash is concentrated more
in the outer layers and decreases in the central parts of the kernel.
The major mineral constituents of the ash are phosphorus, potassium,
silicon, magnesium, calcium, sodium, iron and zinc (Kennedy, 1980) .
The vitamins present in rice include thiamin, riboflavin and niacin. Vitamins are concentrated in the outer layers while the concentration in the endosperm is the lowest as compared to other portions of the kernel (Houston and Kohler, 1970). The rice kernel contains about 0.13 thiamin, 1.54 niacin, 0.14 pyridoxine and 0.04 mg/100 gm riboflavin on a dry basis.
In areas where rice is the main source of food, brown rice would give more than sufficient amounts of niacin, thiamin and phosphorus.
Rice would also provide about 90% of the protein needs and 70% of the zinc requirements. Milled rice would only provide about 50% of the protein, niacin and phosphorus of the RDA's. Since the requirement of energy for men is greater than that for women, 3000 kcal versus
2000 kcal, dietary requirements can be easily met. For men, brown rice would provide more than sufficient amount of protein, iron, phosphorus, niacin and thiamin (Watt and Merrill, 1963). 12
Since rice is low in sodium and fat, it is very suitable for
people on low-sodium or low-fat diets. Also, the ratio of
polyunsaturated to saturated fatty acids is 2:1 (Kennedy and
Schelstraete, 1974).
Rice in the Food Industry
Different modification procedures have been applied to rice and
rice flour to increase their use in the food industry along with
altering their functional properties in certain ways to enable the
food manufacturers to use them in certain product.
Parboiled Rice. Parboiling of rice grains is a very well known
and good method of treating the rice grain to obtain rice with better
cooking characteristics. Parboiling is a moist heat process in which
the starch will change its crystalline form into an amorphus one, due
to the irreversible swelling and fusion of starch. Parboiling is
done by soaking, steaming, drying and milling of rice. The
parboiling process increases the yield of paddy, prevents the loss of
nutrients during milling, salvages wet paddy and prepares rice
according to consumer requirement (Ali and Ojha, 1976).
Modification of rice through parboiling affects the physical properties of rice rather than the chemical properties of rice. The water and heat gelatinize the starch and disintegrate the protein bodies in the endosperm. The starch granules are pressed together, creating strong cohesion between them. Modification of rice by this process brings about sane changes. One of the changes caused by the heat results in sterilization of the rice kernel therefore the kernel can not germinate. The heat will also kill any fungus and any insect 13
infestation; therefore, parboiling will increase or prolong the
shelf-life of rice grains. Hardening of rice kernels will increase
the yield of edible rice and decrease the quantity of broken grains.
Hardness also protects the grain and makes the rice more resistant to
insect infestation and make the grain less able to absorb moisture.
Gelatinization of starch makes the rice swell during cooking due to
the increase in water-absorption capacity. Parboiled rice is more
digestable because grains no longer stick together which means that
grains have more surface area for gastric juices to work on
(Gariboldi, 1972).
Solubilization of sane vitamins and minerals which spread
towards the inside of the endosperm during parboiling, improves the
rices nutritive value. The heat will also inactivate lipase, fuse
thermosoluble substances contained in the germ and spread them
throughout the caryopsis. This will result in a bran richer in fatty
substances and with stand storage better due to the formation of free
fatty acids (Gariboldi, 1972). Parboiling does not affect the
amylose content of rice in a noticable amount, but it will increase
the reducing sugar content of rice.
Parboiling has some drawbacks, such as: parboiling makes
polishing of rice kernels more difficult, the color of the grains will change, the rice attains a rather unique flavor and the grains
are darkened (Gariboldi, 1972).
From the economical standpoint, production and consumption of
parboiled rice offers some advantages. The higher yields increase
the availability of rice for human consumption. The increase in 14
nutritional value of rice is very important especially where people
rely on rice as their main source of nutrients and calories. The
higher cost of parboiling is justified by the increase of rice yield
after milling.
Quick Cooking Rice. Usually it takes about 25-35 minutes to
cook rice depending on the variety and grain size. In some
instances, rice is soaked, boiled, washed and steamed which takes
longer time. The time of cooking depends upon whether the rice to be
served is a plain rice, soup or a casserole type dish (Luh et al.,
1980).
In most cases, quick-cooking rice is precooked for a certain time, then the grains are dried in such a way to retain the grains in a porous and open-structure conditions free from lumps or aggregates
(Roberts, 1972).
Different types of quick-cooking rice products are available currently in the market. They range from relatively undercooked rice which requires 10-15 minutes to prepare or rice requiring 5 minutes to prepare such a "Minute Rice", to a variety which can be ready in a few seconds to 2 minutes. The products that require very short preparation time are usually sold as ready-to-eat breakfast cereals
(Luh et al., 1980) .
Depending on the consumer preference people like cooked rice to be fluffy, light and slightly dry. This has been the target for most quick-cooking rice development during the past 30 years. In Japan and China the approach is different, where people like short grain rice with pasty and sticky characteristics. 15
Different processes are used to produce quick-cooking rice
products, such as, the soak-boil-steam-dry-method, this process is
used by General Foods Corporation to make "Minute Rice". Different
versions of this process have been developed (Roberts, 1952; Campbell
and Hollis, 1954a,b; Shuman and Stanley, 1954; Flynn and Hollis,
1955). The process is summarized as follows: rice is soaked in water
to increase its moisture level to 30% then boiled for 10 minutes
until moisture increases to 70%, then the rice is cooled, washed and
dried with hot air (Luh et al., 1980).
Another process is used to produce expanded and pregelatinized
rice. A patent by Roberts (1955) was issued in which rice is soaked
in water then steamed under pressure at 10-15 psi for 5-10 minutes
and then dried at low temperatures. Finally the grains are puffed in
a hot air stream. This process is needed to produce flavored rice
dishes or casserole type products. Wayne (1963a) heated a
pregelatinized rice in a fluidized gas stream at high temperature.
While Mickus and Brewer (1957) heated the dry parboiled rice in a hot
air to expand or puff the grains in order to obtain a quick-cooking
rice product.
Another process for making quick-cooking rice involves rolling,
compressing or bumping to make thin cracks in the kernels thus
causing a high moisture absorption capacity. Parboiled rice or
pregelatinized rice is usually used. The rice is soaked in water or
steamed to increase water level then compressed and dried at a high
temperature (Ozai-Durrani, 1956). Low drying temperature was also used rather than the high temperature so the grains would have a hard 16
glassy texture rather than a porous one in order to use the product
in dry soup mixes (Unileverr 1957).
Quick-cooking rice is also produced by a dry heat treatment.
This process consists of drying rice grains by removing 3 to 5% of
its water content using hot air of different temperatures (Alexander,
1954; Baraet and Giesse, 1961).
Addition of the freeze-thaw process to the previously developed
series of steps of soaking, boiling and drying had been done
(Keneaster and Newlin, 1957). The parboiled rice was saturated with water for 16 hrs at room temperature. The rice was refrigerated to
32°F and held at the temperature for a few hours. The colloidal
starchy structure will break down by the formation of ice crystals
and produce porous grains. The grains will absorb water readily during the recooking process. Following the rice freezing period, rice is subjected to a fast freezing to a lower temperature. Then
rice grains are thawed and dried.
Gun Puffed Rice Products. Gun puffed rice is a very important method used for many years to produce breakfast cereals such as puffed rice and other puffed cereals. The process is accomplished by using conditioned grains and placing them in a puffing gun. After removal of air, steam is used to increase the pressure, then the pressure is released by releasing the grains into an expansion chamber under high vacuum (Carman and Allison, 1953a,b). Gun puffing can be used to produce quick-cooking rice providing that grain size
should not enlarges more than 2 to 3 times the original size of the raw rice grains. In addition to all the methods that have been 17
discussed, freeze-drying is also used to produce quick-cooking rice products (Wayne, 1963b).
Production of quick-cooking rice using chemicals has been practiced. An example is the use of saturated sodium chloride
solution at 80 C to partially pregelatinize the rice starch. Rice
should be cooked in a large amount of water to make it palatable and decrease the salt level in the final product (Lewis and Lewis, 1965).
Li et al. (1976) used hemicellulase enzymes to soften and remove the outer layer of unhulled rice while leaving the germ intact.
Prior to the enzyme treatment, rice is soaked in slightly alkali solution for 2 hrs and then neutralized with hydrochloric acid. The rice is then washed with water. The resultant enzyme treated rice is superior in its taste. Other chemicals such as wetting, emulsifying, solubilizing and foaming agents had been used. Fatty acid glyceride powder was used to prevent rice clumping upon steaming the rice (Li et al., 1976). Phosphate and polyphosphate solutions had been used to soak rice grains. The rice is cooked in a solution containing phosphate, saccharide and surfactant until most of the starch is gelatinized then dried rapidly (Tanaka and Yukami, 1969).
Breakfast Cereals. Rice breakfast cereals are divided into those which require cooking before serving and those which are ready to eat type. The first type is made from granulated milled rice while the second type can be made from the entire grain or from its milled product as well as fabricated rice products in the form of dough cooked in various ways.
Rice puffing or puffed rice is produced in the United States using short-grain rice. Puffing is accomplished either by sudden 18
application of heat to obtain the necessary rapid vaporization of
water or by pressure drop process which involves sudden transferring
of superheated moisture particles into a space at low pressure. The
former process is much more widely used (Matz, 1970; Hogan, 1977b) .
The sudden expansion of water vapor (steam) will cause the particle
to puff. Then the particles are dehydrated to maintain their
expanded state. Oven or gun puffing is used to prepare puffed rice
products.
Extruders are being used to prepare puffed breakfast cereals as
well as snacks. Superheated and pressurized dough is used. This
dough is usually extruded through an small opening into the
atmosphere. The water vapor expansion upon pressure release results
in products with a very large volume (Luh and Bhumiratana, 1980).
Rice is also used for making rice flakes (Hogan, 1977b) . Rice
is cooked for a certain time under pressure then cooked under
atmospheric pressure for longer time. The cooked rice is then dried
to 17% moisture and after drying the rice is flaked on large smooth
rolls. The pressure is adjusted for the flaking rolls so that the
flakes are well blistered after toasting. Toasting is done by
special ovens to dry the flakes to 3% moisture.
Shredded rice cereal is also a very popular item. This product
consist of rice, sugar, salt and malt. The moisture content is about
3% in the final product. Rice is cooked with other ingredients, then dried to seme extent and tempered in stainless steel bins. Shredded
rice is then made using shredding rolls similar to those used to make
shredded wheat cereal (Luh and Bhumiratana, 1980). 19
Other methods of food preservation such as canning, freezing and
freeze-drying are used to increase the consumption of rice by
introducing new convenient products to consumers. Different canned
rice products are available now such as soups with rice, meat and
rice dinner, casseroles, poultry and rice product, fried rice and
canned rice pudding (Bums, 1972) . Texture of canned rice may be
influenced by varietal differences, age of grain, parboiling
treatment and processing techniques. Varietal differences have been
attributed to variations in amylose content (Kester, 1959). Long
grain rice which has high amylose content tends to be dry, flaky and
bland. In contrast, short and medium rice varieties which have low
amylose content tend to be sticky, moist and better tasting. High protein rice needs longer cooking time because protein which
surrounds the starch molecules acts as a physical barrier to water
absorption, while low protein rice is more tender, needs less cooking
time and has a sweeter taste (Juliano et al., 1965).
Rice can be canned in excess liquid which is referred to as "wet pack" or canned free of moisture, "dry pack". Parboiled rice is usually cooked then washed with cold water, canned, sealed and retorted. Oil can be used to prevent cohesiveness. The problem of canned rice is the clumping of the grains and the difficulty of removing the product from the can. Research had been done to minimize that problem. Ferrel and Kester (1959) and Ferrel et al.
(1960) succeeded in reducing grain clumping by using oil emulsions and other surfactants. Buffalo butter and hydrogenated vegetable oil had been used in India to overcome this sane problem (Sripathy 20
et al., 1960). Verity and Allen (1964) used freezing to breakdown
the excess starch in the can fluid to prevent the starch of forming a
gel like material in the can. Due to the difficulties accompanying
rice canning, few canned rice products are available commercially
(Luh and Liu, 1980). One big problem is the rupturing of the rice
starch granules upon heating the rice at high temperature. Grains
will be destroyed and leaching will occur in the can. Rutledge et
al. (1972, 1974) and Rutledge and Islam (1973, 1976a, 1976b)
successfully produced canned rice with desirable sensory properties
by cross-linking white rice using epichlorohydrin. Cross-linking the
starch decreased, leaching dramatically and increased the stability of
the product during thermal processing. The cross-linked rice was
proven to be superior in comparison with the untreated rice's in
general appearance and taste. Additionally, no clumping occurred in
the cross-linked rice.
Frozen rice is also another convenient item to use since it
requires less time to prepare than raw rice. A study done by Boggs et al. (1951) showed that frozen rice is equal to the freshly cooked rice with respect to color, flavor and texture. In another study
Boggs et al. (1952) used brown rice and found that even after a prolonged period of storage of up to one year, the hydrated frozen brown rice was undistinguishable from the fresh cooked brown rice.
Ragab (1971) developed a method to produce frozen rice by roasting rice in fat then cooking it in water, packing and freezing.
Dehydrated rice using a freeze drying technique has also been developed. Blanchard (1972) and Huber (1972) developed a freeze 21
dried rice product that can readily be rehydrated. The problem of
freeze dried rice is cost, due to high cost of production this method
of preparing rice product may not compete with other methods of production of quick-cooking rice.
Rice in the form of flour or whole grain is used for manufacturing baby food formulas, especially in meat and vegetable combination (Luh and Woodroof, 1977). The largest use of rice in this industry is in making precooked infant rice cereal. Precooked
infant cereals are usually prescribed as the first solid food for
infants. It is an excellent vehicle to introduce essential vitamins and minerals into the infant diet. Hogan (1967, 1977b) discussed the process of making precooked infant cereal. Each food manufacturer has his own formulation to prepare such products and different ingredients are being used in the formulation of precooked rice cereals which includes several vitamins and minerals. The production of rice cereal is more difficult than other cereals. More attention has to be given to control the process of producing rice cereals in order to produce flakes with good quality. Emulsifiers were used to prepare a dried rice cereal product which is rapidly reconstitutable with liquid to form a smooth textured rice cereal suitable for infants (Kelly, 1972). Billerbeck et al. (1970) produced rice cereals with fruits. Addition of strawberries to precooked rice cereals is becoming more favorable by consumers. The increase of the product hygroscopicity due to the presence of fruits and sugar requires the use of moisture proof packages. Antioxidants usually are added to the packaging materials to prolong the product shelf 22
life (Luh and Bhumiratana, 1980). A new and sophisticated process to
lower the liquid requirement for reconstitution is being used now.
The enzyme diastase is used for that purpose by hydrolyzing part of
the starch (Luh and Buhmiratana, 1980).
Rice is also used to prepare formulated baby foods. It is used
in meat, fruits and vegetables puree of their soups. Rice is used in
such products not only as a food ingredient but also to give a
desirable consistency to the products (Luh and Kean, 1975; Luh and
Woodroff, 1975). A new low cost infant food had been developed by
Bhumiratana (1975), the product is high in rice protein. It is a
rice flour based product and is suitable for infants and young
children.
Rice is also used in manufacturing of other food products usually preferred by certain ethnic groups as in certain areas of the world.
Modification of Starches and Their Uses in the Food Industry
Rice is about 90% starch on a dry weight basis. Modification of cereal starches is done to alter the properties of starches in order to make starches more suitable for use in different food products.
Methods that are currently used to modify starches are discussed below.
Acid modification. Acid modification of starch is obtained by the action of acid on starch in a water suspension at sub-gelatinization temperature. Acid modified starches have a lower pciste viscosity thus making them easy to pour into molds. The acid hydrolysis will also improve the gel formation upon cooking 23
due to hydrolysis of amylopectin and the increase of amylose fraction
which is responsible for gel formation. The acid treatment also
increased the clarity of starch pastes (Osman, 1967).
In the food industry acid modified starches are being used in
gum confections particularly the non-waxy cereal type starches, due
to their ability to form concentrated hot fluid pastes which set to
form gels upon cooling (Shildneck and Smith, 1967) . Acid modified wheat starch has been proposed as a replacement for flour in angel
food cakes. Acid modified starch is also used in other industries
such as in the manufacturing of textiles, in sizing and fabric
finishing, in paper manufacturing to improve scuff resistance and printability and in laundries where acid modified starch improves the penetration and distribution qualities of the starch, thus improving the fabric appearance (Shildneck and Smith, 1967).
Oxidized starches. This method is carried out in a similar fashion to that of acid-modification but instead of using acid, alkaline hypochloride is used in this method. The most noticable physical characteristic of oxidized starches is the whiteness. The bleaching effect on the starch depends on the degree of oxidation.
Oxidized starches are very sensitive to heat (Scallet and Sowell,
1967) . Granules of the oxidized starch lose birefringence at a lower temperature with less degree of thickening than that of unmodified starches. Upon cooling the starch exhibits more clarity and fluidity.
Oxidized gel strength is reduced in comparison to that of natural starch (Osman, 1967). Therefore, oxidized starch is more suitable in the manufacturing of candies with tender texture and high 24
clarity. Recently an oxidized starch has been introduced in dry
gelatinized form and proposed for use in the food industry as a
thickener (Scallet and Sowell, 1967).
The major use of oxidized starches is the paper industry for
surface sizing and pigment coating of paper. Oxidized starches also
are useful in textiles, laundry finishing, and building materials.
Cross-linked starches. Starch granules usually swell and
ultimately break down upon cooking. The swelling and breakdown can
be controlled by cross-bonding or cross-linking among the starch
molecules. This method of modification is used specifically to
modify waxy cereal starches. Cross-linking is a mechanism by which
different polyfunctional groups insolublize the starch (Kerr, 1950).
With the shortage of certain starches such as tapioca starch
after World War II, the food industry did not have a starch that would give the clear, non-congealing paste that is desirable in many
food applications. Waxy c o m starch was introduced in 1942 with a
stringy cohesive paste that breaks down too rapidly. Those stringy
characteristics are not acceptable to the food industry.
Cross-linking can overcome such problems (Hullinger, 1967) . By varying the degree of cross-linking an excellent thickener can be
obtained and withstand severe treatment of high pressure jet cooking,
retorting, low pH in pie filling and salad dressing (Hullinger,
1967).
Cross-linked starches are resistant to acid hydrolysis, swelling
and form clear gels. These characteristics make cross-linked
starches preferable in manufacturing pie filling, canned soups, 25
Chinese foods, baby foods, desserts and spaghetti sauces (Schoch and
Elder, 1955). In addition, cross-linking has been used to improve
the quality of canned rice (Rutledge et al., 1972, 1974).
Cross-linked starches are also used in different non food
applications such as, glove dusting, paper coating, textile printing,
oil well drilling muds, paints, insecticides or herbicides
(Hullinger, 1967).
Starch phosphates. The hydroxyl groups in the starch can be
esterified with one or more of the acidic functions of phosphoric
acid. The resultant polymers have been described as inhibited or cross-bonded starches, since the formation of the di- or triesters bonds gives a cross-bonded network in which two or three starch
segments are bonded together. The cross-linking restricts starch granule swelling when cooked in water (Hamilton and Paschall, 1967).
Different chemical compounds have been used to cross-link starches.
Retrogradation or insolubilization of starches can be reduced by replacing some of the hydroxyl groups with other groups or introducing ionizing groups which cause the repulsion between starch molecules.
The introduction of strong acid groups may increase the stability of starches even more and the starch phosphates in which sane of the phosphate groups are monoesters are highly resistant to retrogradation during freezing and thawing (Osman, 1967). Starch phosphate solutions also have high clarity and high water-binding capacity and the ability against gel formation.
Due to the fact that starch phosphates have the ability to thicken without gelling, they are excellent for use in gravies, cream 26
soups, sauces, pie filling and baby foods (Hamilton and Paschall,
1967). Furthermore, starch phosphate improves the freeze thaw
stability of products subjected to such treatment. On the other hand, the untreated starches exhibit considerable syneresis and
liquid separation upon thawing or when the product is stored at low temperatures above freezing. Starch phosphates had been rated as the best choice in their freeze-thaw stability when compared with c o m starch, pregelatinized, cross-bonded waxy starch, all purpose flour and gelatinized c o m starch (Albrecht, 1958; Albrecht et al., 1960).
Some of the uses of starch phosphates in the food industry were salad dressing, puddings, instant dessert powder and instant pudding
(Evans, 1959; Korth, 1959; Neukom, 1958; Kerr and Cleveland, 1962;
Klostermann, 1963).
Pregelatinized starches. The starch is subjected to precooking, followed by drying. In addition to the common property of being cold water-dispersable, a greater weight of pregelatinized starch is needed to produce a given viscosity them the weight needed to get the same viscosity using the natural starch. One of the largest uses of pregelatinzied starch is in the instant pudding packaged powders.
The powder consists of pregelatinized starch, sugar and flavoring.
These powders are ready-to-eat after whipping in cold milk. The second largest use of pregelatinized starches is in pie fillings
(Osman, 1967).
It has been shown that pregelatinized starches increase water absorption of cake batters and aid in the entrapment of air and produce a moist cake of good volume (Boettger, 1963). In cake frosting, pregelatinized starch increases the tolerance to varying 27
additions of water and effectively controls the growth of sugar
crystals (Young, 1940; Butler, 1959). Pregelatinized starch is also
used in whipped chiffon-type desserts, doughnuts mixes and cream
puffs (Clausi et al., 1960; Johnson, 1960; Mitchell and Seidel,
1961) . In addition to those uses, pregelatinized starch is used as a meat binder and moisture stabilizer in table-ready meats, dry soups
formulas, candy glazing, for suspending cocoa and as an ice cream
stabilizer (Linn, 1935; Lolkema, 1952; Evans, 1953; Glabe, 1953;
Evans and Nelson, 1956; Corman, 1958).
Starch acetates. Acetylated starch is not a single, well-defined chemical entity but a series of products with property variants.
Acetylation is the substitution of the hydroxyl groups on the glucose units that are available for reaction with functional groups.
The degree of substitution can be up to a maximum of three moles of acetyl substitute per mole of glucopyranose unit, in that case all three available hydroxyl groups on each unit are acetylated.
Acetylation of starch with three substitutent groups on the glucose unit called triacetate and the degree of substitution is three (D.S.
= 3) . Theoretically, starch will contain 44.8% of acetyl groups by weight on an anhydrous basis. Monoacetate and diacetate contains
21.1% and 35% of acetyl groups respectively (Kruger and Rutenberg,
1967).
The tendency of starch solutions to increase in viscosity upon cooling and to set a rigid gel finally is related to the association of amylose molecules. The starch tendency for viscosity increment and to set a rigid gel is related to the association of amylose 28
molecules, acetylation affects the retrogradation or rigidity of
starch gel. Acetylation will also affect the association of
amylopectin branches. This is very important in the food industry
because the association of amylopectin branches causes cloudiness and
syneresis of starch dispersions. Very low amounts of acetylation is
enough to make a desirable change in the rheological properties. The
food manufacturers usually make starches with less than 0.2 D.S. or
5% acetyl to achieve the desirable characteristics of clarity and
resistance to rigidity (Kruger and Rutenberg, 1967).
Methods of acetylation require consideration of the physical and chemical properties of the raw materials, products, and by products as well as the process technology and cost.
Different chemical reagent-catalysts solvent systems had been used to manufacture starch acetate such as acetic acid, acetic anhydride, vinyl acetate and ketone (Traquair, 1909; Middleton, 1928;
Clarke and Gillespie, 1932; Caldwell, 1949; Wolff et al., 1951; Smith and Tuschhoff, 1960; Tuschhoff and Smith, 1962; Panzer, 1963; Smith and Tuschhoff, 1963.
Starch acetates containing 0.5 - 2.5% acetyl are used in foods, these starches have great stability and form a clear gel. As the degree of substitution increases, the stability of the starch increases. Stability of starch is very important especially at low temperature conditions. Even seme starches which have high stability under normal conditions, require acetylation in order to make them stable at low temperature (Kruger and Rutenberg, 1967). Due to the fact that acetylated starches are stable and form clear pastes, they 29
have been used in pie fillings. Acetylation and cross-bonding are
usually combined to treat starches in order to obtain starches with
high stability and clarity in addition to the resistance to viscosity
breakdown at high temperature, shear and low pH. These starches are
used in canned, frozen baked and fried food products (Kruger and
Rutenberg, 1967).
Rice Fleur
Two types of rice flour are presently available in the United
States (Hogan, 1977a) . The first is produced from waxy rice. This
flour has found limited use, primarily in California. It is used in
gravies, puddings and frozen foods. The other type of flour is usually prepared from broken grains of milled rice or from parboiled
rice, the latter would produce a precooked flour. There is a steady demand for rice flours for uses such as baby foods, breakfast foods and meat products. Rice flour is also used in refrigerated dough as a separating powder. Rice flour is used in bakery products to make bread, crackers, waffles, etc.
Commercial rice flours can be made from short, medium and long grain rice. Since rice flour is made from broken grains, its chemical composition is the same as that of the whole grain.
Differences among these flours include protein, lipid and starch content. The use of certain types of rice flour depends upon the characteristics that are important to particular food products.
The constituent that plays the main role in the behavior of rice flour in the food industry is the starch. The protein and lipids play a less important role. 30
In general, starches of high airy lose content as in tire long grain rice have lower peak viscosity (the highest viscosity of starch slurry) upon heating and higher set-back viscosity (the difference between the cooling peak viscosity and the maximum heating peak viscosity) upon cooling with a rigid gel formation. While the starch of waxy rice is low in amylose content, the viscosity is higher upon heating and has a low set-back viscosity upon cooling as compared with long grain rice (Luh and Liu, 1980).
Waxy rice flour is similar in its characteristics to those of waxy type flours frcm other cereal grains (Whistler and Paschall,
1967). The low amylose content and the appreciable amount of a-amylase characterize this type of flour. Waxy rice flour has lower peak viscosity than that of short grain rice flours probably due to the high amylase activity (Deobald, 1972). In addition, waxy rice flour has no set-back viscosity. This flour is very resistant to liquid separation (syneresis) during freezing and thawing. It had been found that waxy rice flour improves the stability of pudding, sauces and gravies. Incorporation of waxy rice flour in these food products gave the most satisfactory results as compared with all other stabilizers and thickening ingredients usually used in such products to increase their stability upon freezing and thawing cycles
(Hansen et al., 1951; Hansen et al., 1953). Stability of gravies at
32°F was 5 to 6 months when waxy rice flour was mixed or substituted for a portion of the wheat flour used in gravies. The stability was increased to at least one year when waxy rice flour was the sole source of starch used in these products. 31
Although waxy rice flour has the same lack of retrogradation
(insolubilization) as any other waxy flours, its unusual stability
over othex" starches may be due to the small size of its starch
granules or to its special structure. Purified waxy rice starch has
lower stability which may be caused by the amylase activity or the
gelatinization induced by the alkali treatment in the production of
the starch as compared to waxy rice flour (Lull and Liu, 1980).
Using air classification methods, researchers have tried
unsucessfully to produce a high protein rice flour (Stringfellow
et al., 1961). That may be due to the small starch granules, and to
the intimate dispersions of the protein bodies throughout the starch matrix: in the endosperm. Later researchers used an abrasion type mill and successfully produced a high protein rice flour. Hogan
et al. (1964) produced a flour with protein level more than twice
that of the original rice kernels. Houston et al. (1964) used CeCoCo mill, a commercial pearling machine of Japanese origin, to produce a high protein rice flour. In another study, it was concluded that high protein rice flour can be obtained from the outer layer of the
rice grains. This is also rich in other important nutrients such as calcium, phosphorus, lipids, thiamin, riboflavin and niacin (Houston et al., 1968).
Rice flours are used in snack foods, cookies, gravies, sauces, pudding, bread and cakes as well as other types of food products. In the orient rice is the main food item and used for the production of various snack foods. Both waxy and non-waxy rice flours are used for this purpose. The waxy rice flour is used to obtain proper texture 32
of the food. In production of puffed products, the waxy or glutinous
rice flour gives more porous texture and expands rapidly upon baking
or popping (Li and Luh, 1980).
Rice crackers are made in Japan from glutinous and non-glutinous
rice. The annua], production of rice crackers in Japan in 1968 was
148,000 metric tons. The industry had many problems mainly because
the techniques were kept secret and the product was traditionally
hand-made. Also, government control of rice distribution and pricing
recently limited the accessability of this raw material. In spite of
all those problems, the future is thought to be promising (Li and
Luh, 1980). Crackers made frcm glutinous and non-glutinous rice are made by using different techniques and manufacturing steps. The main
difference between the two types lie in the cooling treatment. The
difference in the ratio of amylose to amylopectin affects the
expansion rate and the quality of the product (Li and Luh, 1980).
Cake made frcm rice flour is also popular in the Orient.
Manufacturing of rice cake is somewhat similar to that of rice
crackers with a few differences. Rice flour is usually soaked in water then steamed, after that it is kneaded and formed into different shapes then heat pasteurized and cooked to give the final product which is called Mochi (Sakuri, 1975). Other methods of producing rice cake are also known such as the Taiwan process which
is surrmarized by using ground rice with water to form a slurry. Then
the slurry is drained and the rice dough is kneaded with water.
Sugar may be added to sweeten the cake. Other ingredients may be
added such as salt, mono sodium glutamate and raddish (Li and Luh
1980). 33
Bean et al. (1983) concluded that layered cake can be produced
by hydration of rice flour for several hours before using the flour
to make cakes that have good volume. Hydration helped to improve the
volume and eating quality of the cake.
Fried or popped snack products are also available. Every
product has its own unique characteristics and special preparation
technique. Such products are usually fried and expanded upon the
high frying heat. Extruders are used to produce extruded rice
products. Different flavored products are available and very popular
in some areas of the orient. Rice powder is used to make these
products then the products are usually sprayed with flavoring
solution and dried (Li and Luh, 1980).
Rice is used to produce a kind of breakfast cereal in the United
States by toasting rice in an oven. The rice is usually fortified with vitamins and iron. Sugar, salt and malt are added to this product. To preserve freshness of the product, BHA is used. Rice
flour is also used in baby foods, in the formulation of precooked rice cereal, and in meat and vegetable combinations (Luh and
Woodroof, 1977).
Bread Manufacturing
When mixed with water in the proper portions, wheat flour will
form an elastic dough which is capable of holding gas and form a sponge like structure when heated in an oven.
Halton and Scott-Blair (1937) described wheat flour dough as having protein chains that are responsible for its elastic behavior.
The linkage between the protein chains are not equally strong at 34
all points, so when dough rises seme linkages will break and cause
flow deformation. Other linkages will remain intact and give
rigidity to the dough. All these adjustments have to take place in
the presence of a starch-water mixture. The associated rigid
structure makes the complete relaxation of those elastic protein
units impossible. Gluten, a protein, is responsible for elasticity
and extensibility of wheat flour dough and its ability to hold gas in
its structure (Medcalf and Gilles, 1968). When the flour is wetted
with water, the protein particles are arranged into a heterogenous
fashion. Mixing tends to orient the protein particles in a parallel
arrangement, at this point the dough will be smooth which is an
indication to the bakers that mixing is adequate and at this point
exhibits maximum resistance to pull and maximum elasticity as the parallel positioned gluten strands will resist enlongation and will
relax to its original form when the force of enlongation will stop.
Upon prolonged mixing, the dough will become soft and sticky, but it will recover its strength if allowed to rest (Swanson, 1938).
Starch is the major component of any cereal flour, it constitutes 75-80% of the dry weigh of normal wheat flour. While in rice flour, starch constitutes about 90% of the flour dry weight. It was thought for years that starch is an inert filler found in spaces between protein molecules. With the work of various researchers it became apparent that starch did have an important role in flour quality (Medcalf and Gilles, 1968). Harris and Sibbit (1941, 1942) found that starch from different varieties of wheat varies greatly in baking quality. Wheat starch is generally superior in baking quality 35
when compared with starches from other cereals such as rice, c o m and
potato. It is generally accepted that the rheological properties of
dough are contributed by the gluten and to a lesser extent, the
pentosans. Stumberg (1939) suggested that during mixing, gluten
surrounds each starch granule with a layer of protein. He concluded
that granule size should be important for dough mixing properties.
Jongh (1961) prepared bread from wheat starch and water with salt,
yeast and sugar. The bread had a very coarse, irregular structure
and thick cell walls. The addition of glyceryl monostearate caused
the dough to acquire plastic properties and produced a good loaf with
fine crumb structure. These granules can influence the hydration of
the gluten during mixing. Larsen (1964) showed that starch absorbed water faster than gluten, although gluten absorbs more water than
starch. Thus starch plays an important role in the development of
the dough.
Starch may also have a more important role during mixing, the
starch granules may become embedded in the protein matrix and orient
themselves within the protein (Sandstedt and Schamuberg, 1954).
Gracza and Norris (1961), Gracza and Greenberg (1963) and Ponte et al. (1963) studied the effect of starch granules size on the rheological properties of flour. They found that the greater the number of smaller granules present, the greater the viscosity of the dough and the stronger the mixing curves. Starch also plays a role in the fermentation process. During fermentation amylases act on the starch granules and this function of starch as an enzyme substrate is 36
well known. Moreover, the researchers showed that other changes
occur during fermentation. The starch within the protein film became
more oriented which contributed to the strength of the cells which
form during fermentation. The film which forms the gas cells must be
continuous in order to retain the gas. That suggests a strong
relation between protein and starch (Sandstedt and Schaunburg, 1954;
Jongh, 1961; Sandstedt, 1961).
Starch is known to affect the crumb characteristics and the loaf
volume. It appears that starch is necessary in the baking process to
a greater extent than in mixing and fermentation processes. The
physiological properties of starch are very important, in particular,
the gelatinization properties. The action of amylase increases
during baking, this activity continues until the higher temperature
deactivates the enzymes. During baking, starch gelatinizes or swells
to a limited extent due to the relatively small amount of water in
the system. Some leaching-out of the more soluble amylase fraction probably occurs during this process (Schoch, 1965). During baking
the expansion of gas cells causes an orientation of the starch granules within the protein matrix. As the granules swell, they become more flexible. More expansion will tend to stretch the starch granules and increase this orientation. The partially swollen starch granules are flexible and do not break. Their major contribution is
to the loaf volume and crumb structure formed during baking (Medcalf and Gilles, 1968) . The starch will take up water and tend to remove water from the protein, therefore, this will result in a semi-rigid protein structure. 37
Problems Associated With Wheat Flour Bread
Inspite of the fact that wheat flour is the most suitable
ingredient for bread making, some people can't tolerate wheat bread.
People with certain diseases and those who are allergic to the wheat
protein gluten have to have bread made of ingredients other than
wheat flour.
It is known that people with celiac disease and nontropical
sprue are sensitive to food Which contain wheat and rye flour (Dicke
et al., 1953). Celiac syndrome includes several disturbances in which the symptoms, disorders of absorption and nutritional
deficiences are similar. They are gluten induced enteropathy also
known as primary idiopathic steatorrhea, celiac disease (in children) or nontropical sprue (in adults). This disease is of genetic origin, patients have an intolerance to the gliadin fraction of gluten. The mechanism of the sensitivity to gluten is not understood (Robinson,
1972). Patients with this disease have to exclude wheat, rye, oats, barley and any other products that contain those cereals from their diet. Cereals that can be tolerated are rice, c o m and soybean.
Patients having uremia should be placed on a low protein, low electrolyte diet. Uremia, is a term applied to the conditions arising from failing function of the kidney, literally means "urine
in the blood". Several severe disorders in the body occur in uremia patients. The use of a limited amount of high biological value protein has been well documented. This disease is a slow, wasting disease which leads to death. Diet therapy is not new in the therapeutic armamentorium. Bright (1936) used non-specific diets for 38
his uremia patients. Familiar to everyone is the customary low protein, low electrolyte diets usually prescribed to treat uremia.
Giordano (1963) and Giovannetti and Maggiore (1964) reported experiences with a dietary regimen with which gastrointestinal symptoms disappeared and blood urea nitrogen lowered. This regimen provided the essential amino acids and minimized the intake of non essential amino acids. Due to the low protein content of the rice and rice products such as in rice cereals and cream of rice, they are being used in diets of uremia patients who need to restrict their protein consumption and to maintain their caloric needs (Bailey and
Sullivan, 1968).
Researchers have made efforts to produce a gluten free bread which would be suitable for patients with celiac and other related disease. McGreer (1967) used cellulose gum to formulate bread using gluten-free wheat flour. In another study, a gluten-free bread was produced based on the Giordano-Giovannetti diet for uremic patients.
The bread was low in protein and low in electrolytes. Wheat or c o m starches were used with electrodialyzed whey as the protein source.
Carboxymethyl cellulose, monostearate and guar gum were used in the formulation of the bread (Smith, 1971) . A yeast leavened low protein bread was made in an attempt to produce low protein bread for patients with special diet requirements. Wheat starch was used as a base for the bread in addition to the yeast, monostearate and other ingredients (Steele et al., 1965). Sorenson (1970) used wheat starch as a base for phenylketonurea (PKU) patients. The main ingredient used for helping the dough to hold gases and produce bread with a 39
good loaf volume was msthylcellulose. Jongh (1961) concluded that in
order to make bread from wheat starch or bread based on starchy
materials, a substance for binding among starch granules has to be of
a certain strength and type to be effective in producing bread from
non wheat materials. There are three criteria which have to be met:
first, coherence among starch granules should be great enough to
prevent the dough from becoming leaky during fermentation and
expansion during baking; secondly, the coherence should leave enough mobility to the dough constituents to enable the dough to rise; and
finally, the binder should ensure that the bread crumb gains the
elasticity and softness desired for palatable bread. It has been
found that fat, glyceryl monostearate, egg white and gliadin can be used with wheat starch as binding substances (Kim and De Ruiter,
1968). Swelling agents such as carboxymethyl cellulose, gums, pregelatinized starches and surfactants such as lecithin and monostearate were used to produce a bread from wheat starch and low
fat peanut flour. Water, sugar, fat, yeast and salt were also added
in the mix. The results showed that bread made from wheat starch and peanut flour have volume as compared to wheat bread and the amount of water needed to make the dough was considerably mare than the amount of water needed to make the usual wheat bread (Kim and De Ruiter,
1968) . Kim and De Ruiter (1968) compared the use of different protein sources and starch components in bread making. The results
indicated that loaf volume, which is used usually to judge bread quality, varied according to the type of protein and starch used to make the loaves. Mixer speed, amount of water added, proofing time, 40
mixer type, variation of the amount of ingredients added to the flour
or the starch affects the quality of bread loaves produced from
different starch based doughs.
Sorghum and barley flours have been used to produce breads with
the idea of increasing utilization of those cereals especially in
areas where wheat is not produced in enough quantities for the
internal consumption (Hart et al., 1970). This study showed that
sorghum and barely breads can be made successfully by including methylcellulose in the formulation. Com, tapioca, arrowroot and
potato starches were used in association with sorghum starch to
produce sorghum bread.
Rice flour was used to substitute for some of wheat flour in bread making. This study showed that replacing wheat flour with 30%
rice flour produced an acceptable bread. Replacing wheat flour with
rice flour increases the protein efficiency ratio of bread by 9.1%
and rat growth by 7.7%. Although wheat bread contains a higher
amount of protein than that of rice-wheat bread, it appears that the
amino acid patterns of the rice wheat bread were responsible for the better protein efficiency ratio. The rice-wheat bread required only about 25% more yeast than the usual amount used wheat bread. Such bread could be very important for many nations economies
(Mosqueda-Suarez, 1958) . Very little work has been done in using rice flour to produce 100% rice bread or related products such as cakes. Nishita et al. (1976) investigated the use of rice flour to produce rice bread. Flour from a blend of short and medium grain rice was used. Water, methylcellulose, sugar, salt and oil were also 41
added to the flour mixture. The resulting bread had acceptable characteristics when compared to wheat bread. Rice cake was also made from rice flour (Bean et al., 1983). A modification of an existing method to produce layer cakes was used and the results indicated that hydration of rice flour increases the eating quality of rice layer cake. Cake made from flour hydrated for 6 hours had better crust color, larger volume and less gurnmyness or pastiness as compared with cake produced without a hydration period. Chapter III
MATERIALS AND METHODS
Rice flour, RM-100, was obtained from Riviana Food Inc. The
flour was kept refrigerated at 4°C until needed.
Preparation of Modified Rice Flour
Modification of rice flour was accomplished by a modification of
the method of Caldwell (1949).
Chemical control. Treatment of rice flour involved the addition
of 100 parts of flour to 125 parts of distilled water. Sufficient
sodium hydroxide or sodium carbonate was added to the flour/water mixture to raise the pH to 10-11. The treatment was carried out for
1, 6 and 18 hr. Then the flour pH was adjusted to 6.5 and the flour
was washed and filtered with cheese cloth. During filtration the
flour slurry was subjected to pressure to facilitate the filtration
process. The flour was then dried using a fluidized bed drier.
Chemical treatment with anhydrides. Sodium hydroxide or sodium
carbonate was added to a mixture of 100 parts flour in 125 parts
distilled water to raise the pH to 10-11. Acetic anhydride or
succinic anhydride were added to the flour slurry to lower the pH to
7.0. Alternating addition of alkali and anhydride was continued in
the same manner until all the anhydride was added. Based on the
flour weight, 0.1, 1.0 and 5.0% of the anhydrides was used. The
reaction was carried out for 1, 6 and 18 hr. After each treatment
the flour pH was adjusted to pH 6.5 then washed, filtered and dried
42 43
in the same manner as previously discussed in chemical control treatments.
Moisture
Moisture was determined by the method described by the AACC
(1976). Samples rice flours were dried in a precision gravity convection oven for one hour at 130°C (+/-1°C). Moisture was calculated as percent of weight loss by the sample.
Crude Fat
Crude fat was determined by the Goldfish method described by the AACC (1976) . Five grams of flour was dried in a vacuum oven.
Samples were then extracted for 4 hr using petroleum ether as the solvent.
Ash
Ash was determined by the method described by the AACC (1976).
Two grams of rice flour samples were weighed into combustion crucibles placed in muffle furnace at 600°C for 2 hr. The samples were cooled and the ash content was calculated.
Protein Determination
Nitrogen content of the rice flours was determined using the the method described by the AOAC (1980). A conversion factor of 5.95 was used to calculate the percent protein from the nitrogen content of rice flour.
Color Determination
The color of tire rice flours was determined using a Hunter Lab
Color Difference Meter Model D-25 to compare the color of modified 44
rice flour with that of rice. The unmodified rice flour was used as a control. The control L, a and b values were compared with the L, a and b values for modified flours. The total color differences (AE) for modified flours was calculated as follows:
+ (Aa) 2+ (Ab) 2
The total chromaticity difference was determined using the
Hunter Lab Color Difference Meter.
Clarity Measurement
Clarity of different concentrations of flour solutions was determined to evaluate the effect of modification on the clarity or opacity of flour solutions. Flour solutions of 0.5, 1.0, 1.5, 2.0,
2.5 and 3.0% concentration in distilled water were used. Samples were heated in a water bath until the temperature reached 95°C, then cooled to room temperature. The opacity of solutions was determined using the Hunter Lab Color Difference Meter.
Amylograph Analysis
The amylograph analysis was conducted using a Brabender Model
Va-lB Visco/Amylo/Graph.
Sample preparation for the amylograms. A slurry of rice flour was prepared for the amylogram by mixing 45 g of rice flour and 450 ml of distilled water in the amylograph bowl. The pH was adjusted to
6.0 and 3.5 to evaluate the behavior of rice flour at normal and acidic conditions.
Amylograph procedure. The rice flour slurry was first heated to
50°C in the amylography bowl. The slurry was then heated at a constant rate of 1.5°C/min for 30 min to 95°C. The slurry 45
temperature was held at 95°C for 30 min and then cooled at a constant rate of 1.5°C/min for 30 min to 50°C.
Bread Making
Bread loaves from each batch of the modified and unmodified rice flours were made according to a modification of the method used by
Nishita et al. (1976) for making rice bread leavened with yeast. The method used for bread making is given in Table 1.
Table 1 - Rice bread formula
Ingredients Weight(g)
Rice flour (14% Mb.) 100.0 Sucrose 7.5 Vegetable oil 6.0 Baker's compressed YeasJ. 3.0 Methyl cellulose (4000) 3.0 Salt 2.0 Non fat dry milk 1.0 Water 75.0 k Dow Chemical - Methocell 90 Hg 4000 cp
The bread was made as follows: flour, methocel (4000 cp) and dry milk were blended and added to a Kitchenaid Mixer Bowl, containing water, yeast, sugar and salt. Yeast was activated prior to the mixing procedure for 10 min using a mixture of warm water sugar and salt. After adding all the ingredients together, they were mixed for 3 min using a dough paddle attachment. The bowl was then scraped, followed by additional mixing at high speed for three minutes. A constant amount of dough (250 g) was weighed into a well greased small loaf pan and fermented for 1 hr at 86°F. Pans were covered with wet cloth to maintain a high relative humidity. The 46
dough was baked at 350°F for 35 min, then cooled to room temperature and plastic wrapped. The bread was used the following day for physical testing and sensory evaluation.
Bread Volume
Bread volume was measured by rape seed displacement. The volume of the loaf in cubic centimeters divided by the loaf weight in grams gave the volume in term of cubic centimeter per gram (cc/g) or the specific volume of the bread.
Water Activity
Water activity (a ) of the bread was determined using an Aminco w Hygrometer. A small portion of the bread slice was placed in a jar connected to the hygrometer by a sensor to give the relative humidity inside the jar. Then the water activity was calculated from the relative humidity readings using a standard curve.
Texture Analysis
Compressability and toughness of the bread were determined using an Instron Universal Testing Machine Model 1120 equipped with compression and Kramer shear cells.
The elasticity modulus for the compression test was calculated according to the following formulas:
FAC (N/div) = FSL (neutons)/100 (divisions)
DEF (mm) = DC (CRS/CHS)
Force (N) = FAC X F (div) 2 Stress (a) (M/M ) = Force/slice area
Strain (e) (m/m) = DEF/slice thickness 2 Elasticity modulus (N/M ) = Stress/Strain 47
Where: FSL = Full scale load in newtons CPS = Cross head speed mm/min CHS = Chart speed mm/min DEF = Deformation F = Force in division from curve DC = Distance in ran from curve
This information was obtained from the compression curve and the
Instron for measurement of the elasticity modulus (Figure 1).
Toughness of the bread was calculated as the peak high from the
Instron curve divided by the sample weight.
Electron Microscopy of Rice Flour and Bread
Selected flour samples were mounted on aluminum stubs and
sputter coated for 5 min with gold palladium. They were then
examined with a Cambridge stereoscan 150 scanning electron microscope. Selected bread samples were also prepared by cutting
small pieces of the bread crumb then they were freeze dried and mounted on aluminum stubs. The samples were then sputter coated for
8 minutes with gold palladium. The samples were examined using the
same electron microscope mentioned above. This electron microscope
study was done to evaluate the effect of modification on the
structure of rice flour and bread. Wheat bread sample were also examined to compare rice bread structure with that of wheat bread.
Taste Panel Evaluation
Bread loaves from each batch of flour were sliced uniformly into one half inch thick slices. The slices were then randomly presented to the panelists. Nine panelists evaluated the bread slices using a score sheet which is used by the American Institute of Baking to 48
7 F MAX
6
5
4
ARBITRARY POINT
3
2
1
0 DC ->
DEFORMATION (nro)
Figure 1 - A typical compression test curve showing the utilization of the curve to calculate the elasticity modulus. 49
evaluate wheat bread (Dalby and Hill, 1960). The score sheet is shown in Figure 2.
Statistical Analysis
The proximate analysis, opacity, color differences, instron measurements, amylograms and taste panel evaluation results were analyzed by the analysis of variance technique (ANOVA). The F-test was used to determine if significant differences exist among source of variations. When differences were found, means were separated using the Least Significant Differences (LSD) and Duncan's Multiple
Range Test to determine where differences occurred (Steel and Torrie,
1980). 50
SCORE SHEET FOR BREAD
Ideal Actual Penelized for Score Score Volume...... 10 Too small Too large Color crust.... 8 Not uniform Streaked Light Dark Dull Symmetry of form.. 3 Lower end Low side Protruding crust Low middle Uneven top Flat top Shrunken side Small end Evenness of baked... 3 Light side Light end Light bottom Dark bottom "Spotty" bottom Character of crust 3 Thick Tough Hard Brittle Brea): and shred... 3 One side only Insufficient Wild break None No Shred Shell Grain...... 10 Open Coarse Nonuniform Thick cell walls Holes Color of crumb.... 10 Gray, dark Streaky, dull Aroma...... 10 Strong, lack of Gassy Musty, sharp Taste...... 15 Flat, salty, Foreign sour Unpleasant after taste Mastication (chew- 10 Doughy, dry ability) Tough, gummy Texture 15 Rough-harsh, Ridged lumpy Too loose Core, crumbly Too compact Total 100 Average Score Actual Score OQMMENTS:
Figure 2 - Score sheet for bread evaluation. Chapter IV
RESULTS AND DISCUSSION
Proximate Ccsnposition of Rice Flours
The proximate composition of unmodified and modified, rice flours is given in Table 2. Fat, ash and protein were calculated on a 14% moisture basis. The moisture content of unmodified rice flour was
12.5%. The reported moisture content of milled rice samples ranged from 12.0% to 13% (Copeland, 1924; Adam, 1975). Modified rice flours in this study had a mean moisture content of 12.7%. Modified rice flours were subjected to air drying using a fluidized bed drier. The final moisture content of the modified flours can be effected by several factors: length of drying time, drier air speed, size of wet flour chunks and the initial moisture content of the flour.
Moisture content of modified rice flours was lowered to a range that made grinding the dry chunks of flour easy. The moisture level also prevented mold growth during refrigerated storage.
Crude fat content of unmodified rice flour was 0.99% and that of modified rice flours ranged from 0.1% to 0.98%. A wide range for the rice crude fat values has been reported and the variability in those values was largely due to the inherent variability among rice varieties and to differences in analytical techniques used by different investigators (Juliano, 1972b). It had been reported that crude fat for milled rice ranged from 0.2% to 2.7% (Simpson et al.,
1965). Significant differences (P<0.05) in the amount of crude fat
51 52
Table 2 - Proximate analysis of unmodified and modified rice flours
Treatment AnhydrideA Alkali Time % Moisture % Fat %Ash % Prote NaOH 1 13.15 0.42 0.53 6.59 6 14.10 0.51* 0.56 6.54 18 13.55 0.11 0.42 6.41
Na C 0 o 1 8.36 0.23 0.81 6.74 <£ 3 6 9.74 0.58 0.50 6.74 18 14.84 0.29 0.52 6.63
0.1% AA NaOH 1 12.57 0.41* 0.57 6.65 6 11.19 0.19 0.36 6.83, 18 16.07 0.39 0.38 6.04
1.0% AA NaOH 1 12.30 0.56 0.75 6.43 6 12.36 0.50* 0.50 6.74 18 14.59 0.12 0.51 6.28
5.0% AA NaOH 1 13.76 0.28 2.00 6.55 6 15.11 0.43 2.36 6.58 18 11.11 0.37 1.86 6.49
0.1% SA NaOH 1 16.62 0.52 0.75 7.27 6 10.51 0.67 0.75 7.79 18 11.85 0.98 0.69 7.58
1.0% SA NaOH 1 13.05 0.71 1.00 7.43 6 11.52 0.62 1.19 7.60 18 13.25 0.71 1.10 7.41 * 5.0% SA NaOH 1 12.50 0.59 3.03* 7.76 6 12.95 0.98 2.54* 7.21 18 12.70 0.64 2.51 7.26
0.1% AA Na„C0o 1 11.26 0.63 0.60 7.51 3 3 6 13.70 0.22* 0.70 7.00 18 13.55 0.16 0.57 6.75 * 1.0% AA Na-CO- 1 12.60 0.21 1.32* 7.00 2 3 6 11.70 0.73 2.83 7.32 18 7.80 0.30 1.13 7.44 * * 5.0% AA Na q o 1 16.20 0.10 4.92* 7.10 2 3 6 10.15 0.74 5.78 7.56, 18 12.00 0.20 4.11* 5.80
0.1% SA 1 12.20 0.65 0.80 7.64 Na-CO-,2 3 6 15.75 0.87 0.83 7.64 18 11.40 0.61 1.43 7.49 53
Table 2 - Continued
1.0% SA NaoC0, 1 13.45 0.60 1.96* 7.68 z j 6 13.00 0.49 2.58 7.48 18 11.65 0.63 1.85 7.35
5.0% SA Na_C0o 1 13.05 0.53 3.46* 7.64 Z J 6 11.90 0.66 3.58* 7.51 18 15.40 0.59 3.07 7.23
Control (rice flour) 12.05 0.99 0.53 7.68
A M = Acetic Anhydride SA - Succinic Anhydride * Significantly different (P<0.05) frcin the unmodified rice flour (control) 54
were found between the flours treated with acetic anhydride versus
the flours treated with succinic anhydride. Treatment time and
anhydride concentration had no significant effect on the amount of
crude fat in the modified flours. The significant differences that
were found were due to the pressure applied during filtration and
washing of the modified flour slurries after modification, some of
the fat washed out from the flour. Some of the variations in the fat
content of rice flours may be attributed to experimental error..
Ash content of the unmodified rice flour was 0.53% (Table 2).
The reported values for ash ranged from 0.26 to 1.95% (Simpson et
al., 1965). For the modified rice flours, ash content ranged from
0.36 to 5.78%. Statistical analyses indicated that significant
differences (P <0.05) existed between the different modified flours
due to the use of alkali type and the different concentration of the
anhydrides. Analysis of variance revealed a significant (P<0.05)
interaction between the type and concentration of the anhydrides, and
between the alkali and the concentration of the anhydrides used. Ash
content increased with the increase in the concentration of the
anhydride (Fig. 3) . Means for ash content are presented in Table 3.
The increase in ash content of modified flours was higher due to the use of sodium carbonate as compared with sodium hydroxide (Fig. 4).
The means for ash content are presented in Table 4. The increase in
ash content as the concentration of anhydrides increased was due to the increase in anhydrides concentration. Maintaining the pH at a level above 7 during the modification process required continual addition of sodium carbonate and sodium hydroxide. This 55
Table 3 - The effect of acetic anhydride versus succinic anhydride and their concentration on ash content of the modified rice flour
* Treatment Mean ash content
0.1% acetic anhydride 0.53 A 1.0% acetic anhydride 1.17 B 5.0% acetic anhydride 3.59 C
0.1% succinic anhydride 0.87 A 1.0% succinic anhydride 1.61 B 5.0% succinic anhydride 3.11 C
Means followed by the same letter do not differ significantly (P<0.05) according to the Least Significant Difference and Duncan's Multiple Range Test. iue s otn fahdiemdfe ie flours. rice modified anhydride of content Ash - 3 Figure
% ASH 0 1 1 2 2 3 3 . . . . . 0 5 00 . . 50 00 50 50 75 . 1.0 0.1 ------(CONCENTRATION OF ANHYDRIDE (CONCENTRATION OF S U C C D . ’ I C A N H Y D R I D E ACETIC ANHYDRIDE 5.0 56 iue - s cnet f oiid ie lus ne different under flours rice modified of content Ash - 4 Figure concentration of anhydride and alkali. and anhydride of concentration
% % ASH 3 . 0 1 1 2.7 3 3 3 2 . A . . . . . 5 2 0 3 6 - - - - - 0.1 1.0 CONCENTRATION OF ANHYDRIDE OF CONCENTRATION - • S O D I U M C A R B O N A T E SODIUM HYDROXIDE 5.0 57
58
Table 4 - The effect of alkali and anhydride concentration on ash content of modified rice flours
* Treatment Mean ash content
Sodium carbonate + 0.1% anhydride 0.82 A Sodium carbonate + 1.0% anhydride 1.94 B Sodium carbonate + 5.0% anhydride 4.24 C
Sodium hydroxide + 0.1% anhydride 0.58 A Sodium hydroxide +1.0% anhydride 0.84 B Sodium hydroxide + 5.0% anhydride 2.46 C
Means followed by the same letter do not differ significantly (PC0.05) according to the Least Significant Difference and Duncan's Multiple Range Test. 59
increased the amount of sodium in the flour slurry causing the
increase in ash content. Sodium carbonate had more of an effect on
the ash content them sodium hydroxide due to the lower solubility of
sodium carbonate in water as compared to that of sodium hydroxide.
The lower solubility meant that more sodium carbonate (more sodium)
was used to bring about the basic condition during modification of
rice flour. This excess sodium ended up in the modified flour.
The protein content of the unmodified and modified rice flours
are shown in Table 2. The protein content of the unmodified rice
flour was 7.68%, while the protein content of modified rice flour
ranged from 5.80 to 7.79%. Significant differences (PC0.05) were
found among modified rice flours due to the use of acetic anhydride versus succinic anhydride and the use of sodium hydroxide versus
sodium carbonate. The effect of the interaction between alkali and anhydrides on the protein content was significant (PC0.05) (Fig. 5) .
The mean values for protein content are presented in Table 5.
Mean values for protein using acetic anhydride modification were
lower them those using succinic anhydride. The effect of sodium carbonate versus sodium hydroxide was not significant. Significant
interaction between the type of anhydride and the type of alkali on the protein content were found (P<0.05). Samples treated with acetic anhydride in the presence of sodium carbonate and sodium hydroxide had protein content lower than those treated with succinic anhydride.
The loss in seme of the protein content during modification was the increasing nitrogen solubility at higher pH's (Betschart, 1974). 60
Table 5 - The effect of anhydrides, alkali and their interaction on protein content of modified rice flours
* Treatment Mean protein content
Acetic anhydride + sodium carbonate 7.11 A Succinic anhydride + sodium carbonate 7.52 B Acetic anhydride + sodium hydroxide 6.51 C Succinic anhydride + sodium hydroxide 7.48 B
Means followed by the same letter do not differ significantly (P<0.05) according to the Least Significant Difference and Duncan’s Multiple Range Test. modification of rice flour. rice of modification iue - rti cnet s fetd y nyrd ad alkali and anhydride by affected as content Protein - 5 Figure
% PROTEIN 6.5 6.6 6.7 6.8 6.9 7.0 7.2 7.3 7.5 7.6 a NA2CQ3 ALKALI SUCCINIC ANHYDRIDE SUCCINIC ACETIC ANHYDRIDE ACETIC NAOH 61
62
Color and Chromaticity of Rice Fleurs
Total color difference (AE) and total chromaticity difference
(AC) of the modified flours as determined with the Hunter lab color
difference meter are presented in Table 6. For the AE, significant
differences (PC0.05) were found among the modified flours due to the
use of sodium hydroxide versus sodium carbonate. The mean AE value
for flours treated with sodium carbonate was higher than that of
flours treated with sodium hydroxide (Table 7) . Significant
differences (P<0.05) were found among flours due to anhydride
concentrations. Means values of AE at the 1.0% and 5.0% anhydride
levels were significantly higher than that for the 0.1% anhydride
(Table 7) . Interactions between alkali and anhydride concentration
on the AE was significant at the 5.0% level (Table 7). The combined
effect of alkali and anhydride concentration on AE is illustrated in
Figure 6. Table 7 and Figure 6 indicated that mean AE values were
significantly higher for the 1.0% and 5.0% anhydrides when compared
to mean AE values for 0.1% anhydride where sodium carbonate was used
to bring about basic conditions. No significant differences (PC0.05)
existed between flour treated with 1.0% anhydride and flour treated with 5.0% anhydride.
The trends found for total chromaticity difference (AC)
resembled those found for AE. Values are presented in Table 7 and
illustrated graphically in Figure 7.
Some flour samples had considerably higher AE and AC values
(Table 6) . The same samples generally had higher ash content
compared with the rest of samples (Table 2) . The increase in AE and
AC values indicated that the colors of those samples were darker 63
Table 6 - Total color difference (AE) and total chromaticity difference (AC) of modified rice flour
Treatment
Anh.ydr.ideA Alkali Time AEAC
NaOH 1 3.74 2.25 6 1.74 1.30 18 .92 .92
NaOH 1 2.34 1.32 6 2.58 0.90 18 .75 .73
0.1% A A NaOH 1 0.93 0.87 6 1.74 1.06 18 .85 .18
1.0% AA NaOH 1 3.24 1.15 6 1.21 1.00 18 1.70 .40
5.0% AA NaOH 1 3.15 1.40 6 1.47 * 1.49 18 4.42 2.12
0.1% SA NaOH 1 1.21 0.42 6 .36 .21 18 .29 .24
1.0% SA NaOH 1 1.66 1.40 6 1.14 .91 18 .42 .31
5.0% SA NaOH 1 2.64 1.17 6 1.87 1.04 18 .57 .50
0.1% AA Na2C02 1 1.46 .89 6 2.59 1.13 18 2.60 0.65
1.0% AA N a 2C 0 3 1 7.87, 6.67, 6 6.58, 6.26, 18 4.29 3.64
5.0% AA Na2C02 1 8 .22, 7.88, 6 6.36 6.31 18 6.39 5.92 64
Table 6 - Continued
0.1% SA N a oC 0 o 1 1.22 0.50 fa fa 6 0.85* 0.00* 18 5.79 4.92
1.0% SA Na„CO_ 1 8.79* 7.70* fa J 6 8.03 7.50* 18 8.38 3.66 * 5.0% SA 1 7.74* 6.77* N a 2C0E 6 7.07* 6.87* 18 7.33 7.13
Control (unmodified flour) 0 0
* Significantly different (P<0.05) from the control
A AA = Acetic Anhydride, SA = Succinic Anhydride 65
Table 7 - Mean values of total color differences (AE) and total chromaticity differences (AC) for modified rice flours as influenced by the concentration of anydrides and alkali
* * Treatment AE AC
Sodium carbonate 5.3750A 4.6889 A Sodium hydroxide 1.7150 B 0.8822 B
0.1% anhydride 1.6742A 0.9225 A 0.1% anhydride 4.1167 B 3.3842 B 5.0% anhydride 4.8442 B 4.0500 B
0.1% anhydride + sodium carbonate 2.4517 A 1.3483 A 1.0% anhydride + sodium carbonate 6.5050 B 5.9050 B 5.0% anhydride + sodium carbonate 7.1683 B 6.8133 B
0.1% anhydride + sodium hydroxide 0.8976A 0.4967 A 1.0% anhydride + sodium hydroxide 1.7283 A 0.8633 A 5.0% anhydride + sodium hydroxide 2.5200 A 1.2867 A
Means followed by the same letter do not differ (P<0.05) according to the Least Significant Difference and Duncan's Multiple Range Test. ifrn cnetain f nyrds sn sdu croae and carbonate sodium using anhydrides of concentration different iue - oa clr ifrne o rc for tetd with treated flours rice of differences color Total - 6 Figure sodium hydroxide. sodium
TOTAL COLOR DIFFERENCE (AE) 0.5 2.0 2.5 0 5 0 5 0 o 0.1 CONCENTRATION OF ANHYDRIDE OF CONCENTRATION 1.0 - SODIUM CARBONATE SODIUM HYDROXIDE 5.0 66
67
6.5
6.0
5.5 U < 5.0 LEGEND:
SODIUM C\RBONATE M SODIUM HYDROXIDE a 3.5 M£ U M
0.1 1.0 5.0
CXM2NTRATI0N OF ANHYDRIDE
Figure 7 - Total chromaticity differences for rice flours treated with different concentration of anhydrides using sodium carbonate and sodium hydroxide. 68
(yellowish) than the color of the control flour (unmodified rice
flour).
The relationship between high ash content (mineral) and the
darkening of flour color has been documented by several
investigators. It has been reported that color differences among
cereal flours were attributed to differences in carotenoid pigments.
Cellulosic materials and mineral content (Patton and Dishaw, 1968;
Sheuey and Skarsaune, 1973). Gillis (1963) and Sheuey and Skarsaune
(1973) reported a high correlation between ash content of wheat
flour and the reading of the Agtron which is an instrument used to determine flour color reflectance values.
Clarity Measurements
Clarity of starch paste is a quality which is of interest to
food manufacturers. Starch clarity is an important criteria on aesthetic consideration. It is of special importance when starch is used as a thickening agent for fruit pie fillings. Pie filling
should have a fairly transparent paste, not a dull muddy appearance.
In constrast to clarity, opacity is also important in salad dressing or in instant dessert type products. Clarity measurements for modified rice flours were obtained using a Hunter lab color difference meter to measure the opacity of flours. The results are illustrated graphically (Figs. 8 - 21). A decrease in the opacity of rice flour solutions or an increase in clarity was noted in comparison with the opacity or clarity of the control (unmodified rice flour).
Treatment of rice flour with sodium hydroxide resulted in a decrease of rice flour solution opacity as compared with that treated 69
LEGEND
CONTROL
FLOUR CONCENTRATION (%)
Figure 8 - Opacity of rice flour treated for 1, 6 and 18 hours with sodium hydroxide. Figure 9 - Opacity of rice flour treated for 1, 6, and 18 hours with 18hours and 6,carbonate. 1,sodium for treated flour rice of 9-Opacity Figure
% OPACITY 21 15 24 18 30 27 33- 6- 3 39- 42- 45 48 51 - 4 5 57-1 0.0 ------11 0.5 ..
■ — FLOUR (%)CONCENTRATION 1.0 ......
. D N E C E L 1.5
— ------2.0
i 2.5
- CONTROL - —r •— — 3.0 70 Figure 10 - Opacity of rice flour treated for 1, 6 and 18 hours with 18hours and 6 1, for treated flour rice of 10-Opacity Figure 1.0% acetic anhydride and sodium hydroxide. sodium and anhydride acetic 1.0%
% OPACITY LU OCNRTO (%)FLOUR CONCENTRATION LEGENDr CONTROL 71 Figure 11 - Opacity of rice flour treated for 1, 6 and 18 hours with hours 18 and 6 1, for treated flour rice of - 11Opacity Figure 1.0% acetic anhydride and sodium hydroxide. sodium and anhydride acetic 1.0%
% % OPACITY 12- 21- IS 27 1S- 30 . 2.0 0.0 0.5 LU 3NETAIN (%) C3CNCENTRATI0N FLOUR 1.0 // LEGENDi 53.0 1.5 2.5 CONTROL 72 iue 2-Oaiyo rc for rae fr , ad 8 or with hours 18 and 6 1, for treated flour rice of 12-Opacity Figure 5.0% acetic anhydride and sodium hydroxide. sodium and anhydride acetic 5.0%
% % OPACITY 12- 21 24- 15- 10 27 30- 33- 36- 39- 42- 45- 48- 51- 54- 57- 0.0 - - . . 15 . 2. 3.0 .5 2 2.0 1.5 1.0 0.5 V / 1 / '/ I LU OCNRTO (%) CONCENTRATION FLOUR i D N E C E L 16 CONTROL 73 74
LECEND.
CONTROL
Figure 13 - Opacity of rice flour treated for 1, 6 and 18 hours with 0.1% succinic anhydride and sodium hydroxide. Figure 14 - Opacity of rice flour treated for I, 6 and 18 hours with 18hours and 6 I, for treated flour rice of 14- Opacity Figure 1.0% succinic anhydride and sodium hydroxide. sodium and anhydride succinic 1.0%
% OPACITY 15- 16- 27- 30- 33- 39 42- 48 54- 57 6CM 0.0 0.5 LU OCNRTO (%) CONCENTRATION FLOUR 1.0 1.5 2.0 CONTROL 3.02.5 75 76
6CH
57
54~]
484
454
42-
y cl 3 3 0 4 27-1 244 LEGEND• 214 164 16 CONTROL ’H 0.0 0.5 1.0 1.5 2.0 2.5 3.0 FLOUR CONCENTRATION (%) Figure 15 - Opacity of rice flour treated for 1, 6 and 18 hours with 5.0% succinic anhydride and sodium hydroxide. Figure 16 - Opacity of rice flour treated for 1, 6 and 18 hours with hours 18 and 6 1, for treated flour rice of 16-Opacity Figure 0.1% acetic anhydride and sodium carbonate. sodium and anhydride acetic 0.1% % OPACITY 15- 18- 27 30 33 42 45 57-1 0.0 0.5 LU CCJRTO (%) OCNCHJTRATION FLOUR 1.0 . D N E G E L 1.5 2.0 . 3.0 2.5 CONTROL 77 Figure 17 - Opacity of rice flour treated for 1, 6 and 18 hours with 18hours 6and 1, for treated flour rice of Opacity - 17 Figure 1.0% acetic anhydride and sodium carbonate. sodium and anhydride acetic 1.0% % % OPACITY 12- 15- 27- 30- 33 33 42 45- 54- 0.0 LU OCNRTO (%) CONCENTRATION FLOUR 1.0 - D N E G E L 2.0 2.50.5 1.5 COKTROL 3.0 78 Figure 18 - Opacity of rice flour treated for 1, 6 and 18 hours with 18hours 6and 1, for treated flour rice of Opacity - 18 Figure 5.0% acetic anhydride and sodium carbonate. sodium and anhydride 5.0%acetic % OPACITY 12- 21 24- 15- 0.0 . 1.5 0.5 LU OCNRTO (%) CONCENTRATION FLOUR 1.0 LEGEND■ 2.0 2.5 CONTROL 3.0 79 Figure 19 - Opacity of rice flour treated for 1, 6 and 18 hours with 18hours 6and 1, for treated flour rice of -Opacity 19 Figure 0.1% succinic anhydride and sodium carbonate. sodium and anhydride succinic 0.1% % % OPACITY LU OCNRTO (%) CONCENTRATION FLOUR CONTROL 80 81 57-1 5 4 - 46- 45 - 42 39- 3 6 - Me 33- 04 o OP 30 - 27 24- 21 16- 15- CONTROL 1 2 -1 0.0 0.5 1.0 1.5 2.0 2.5 3.0 FLOUR OTNCENTRATION (%) Figure 20 - Opacity of rice flour treated for 1, 6, and 18 hours with 1.0% succinic anhydride and sodium carbonate . Figure 21 - Opacity of rice flour treated for 1, 6 and 18 hours with 18hours 6and 1, for treated flour rice of Opacity - 21 Figure 5.0% succinic anhydride and sodium carbonate. sodium and anhydride succinic 5.0% % % OPACITY 12- 15- 21 18- 27 57- 0.0 - LU OCNRTO (%) CONCENTRATION FLOUR 1.0 1.5 V / 2.0 2.50 .5 OTOi. CONTRO 3.0 82 83 with sodium carbonate (Fig. 8, 9) . The highest clarity was obtained using sodium hydroxide for 18 hr, as compared with 6 and 1 hr treatments. While treatment of flour with sodium carbonate for 1 hr resulted in lower opacity values as compared with treatment of flour with sodium carbonate for 6 and 18 hr. Modification of rice flour with 0.1%, 1.0% and 5.0% acetic anhydride with sodium hydroxide resulted in a decrease in opacity or increase in clarity of rice flour solutions. Flour treatment with 0.1% and 1.0% acetic acid with sodium hydroxide for 6 hr and that treated with 5% acetic anhydride for 18 hr were more effective in increasing the clarity of rice flour solution in comparison with the same treatments for different times (Figs. 10, 12) . Treatment of rice flour with succinic anhydride and sodium hydroxide did not noticably affect the clarity of flour solutions particularly at higher concentrations (Figs. 13, 15) . Modification with acetic anhydride and sodium carbonate also increased the clarity and decreased the opacity of rice flour solutions (Figs. 16-18). The most effective treatment in lowering the opacity was the 5.0% acetic anhydride for 1 hr (Fig. 18) . Opacity measurements of rice flours treated with succinic anhydride find sodium carbonate are represented in Figures 19-21. Here again, modification of rice flour resulted in increased solution clarity. Treatment of rice flour with 0.1% succinic anhydride for 1 and 6 hr was not effective in lowering the opacity values as compared with the rest of the succinic anhydride treatments. Clarity of starch solutions, apart from the eye appeal, related to the dispersion and retrogradation or insolubilization of the 84 starch. The high amylose starches tended to retrograde due to the amylose (linear fraction) aligning themselves into an associated pattern and setting into a firm gel. Waxy starch (no linear fraction) is the most transparent starch when in solution. Modification of starches chemically will substitute some of the hydroxyl groups on the glucose units and prevent the linear starch molecules from aligning themselves into a retrograded pattern. Factors such as concentration of the starch, pH, presence of salts, etc. affects the starch paste clarity (Elder and Schoch, 1959). Amylograph Analysis At Neutral pH The amylogram of the rice flour used in this study (Fig. 22) was typical of non-waxy long grain rice flour slurry at netural pH (Halik and Kelly, 1959). The barbender viscosity of the rice flour was typical of most non-waxy cereal flours, which shows a moderate pasting peak, corresponding to a maximum volume occupied by the swollen granules, a moderate decrease in viscosity upon cooking for a long time due to seme fragmentation and solubilization of the relatively stable granules and a higher increase in viscosity upon cooling due to retrogradation or the insolubilization of the amylose linear fraction of the starch. The pasting temperature of the rice flour was 68°C with an intermediate peak of 820 barbender unit (B.U.) and a relatively high viscosity (770 B.U.) of the cooked paste upon cooling to 50°C. Those findings were in the range of those reported previously (Halik and Kelly, 1959: Webb and Stermer, 1972; Nishita and Bean, 1979). VISCOSITY (BARBENDER UNIT) ZOO- 0 0 3 100 0 0 4 0 0 6 0 0 6 0 0 7 0 0 6 0- - 0 iue 2*Ayorp a H futetdrc for (control). flour rice untreated of 6 pH at Amylograph * 22 Figure 060 30 IE (MINUTES) TIME 85 90 86 The amylograms of the modified rice flours under neutral conditions are presented in Figures 23-36. In general, the modified flours followed the some pattern as the unmodified rice flour. Generally, the peak viscosities of the modified rice flours were lower compared with the peak viscosity of unmodified flour (Table 8). Significant differences (P<0.05) were found in the peak viscosity values among flours treated with acetic anhydride vs. succinic anhydride (Table 9) . Succinic anhydride lowered the peak viscosity of rice flours more in comparison with acetic anhydride. Although the mean values for the peak viscosity of the modified flours were generally lower than that of unmodified rice flour, some flours had higher peak viscosities than that of unmodified rice flour. Those findings were similar to those reported by Kruger and Rutenberg (1967) for c o m and modified c o m starch (starch acetate). Succinic anhydride resulted in a significant (P<0.05) lowering the viscosity after the paste was held at 95°C for 30 minutes (prolong heating peak viscosity) as compared with rice flours treated with acetic anhydride. While the effect of both anhydrides on the setback viscosity was not significant (P<0.05). The mean values for the maximum peak viscosity, viscosity after 30 min. at 95°C and the setback viscosity are presented in Table 9. Significant differences (PC0.05) were found in the setback viscosity values among samples treated with sodium carbonate versus sodium hydroxide. The alkali type did not affect the maximum viscosity and the holding viscosity of the rice flours significantly (P<0.05). The concentration of the anhydrides affected the setback viscosity significantly (PC0.05). The increase in the anhydride VISCOSITY (BARBENDER UNIT) hours with sodium hydroxide. sodium with hours iue2 mlgaha H f ie lu tetd o 1 6 n 18 and 6 1, for treated flour rice of 6 pH at 23- Amylograph Figure 200 300- SOO 600 too- 600 - 0 30 IE (MINUTES) TIME LEGEND« 60 CONTROL 87 VISCOSITY (BARBENDER UNIT) iue2 -Ayorpsa H60o ie lu tetd o 1 6 and 6 1, for treated flour rice of 6.0 pH at -24Amylographs Figure 18 hours with sodium carbonate. sodium with 18hours 200 300 ♦ 500 0 0 6 700 900- 00 0- - 0 30 IE (MINUTES) TIME i D N E G E L CONTROL 88 VISCOSITY (BARBENDER UNIT) iue2 mlgah t H . frc fortetd o 1 6 and 6 1, for treated flour rice of 6.0 pH at -Amylographs 25 Figure 18 hours with 0.1% acetic anhydride and sodium hydroxide. sodium and anhydride acetic 0.1% with 18hours 200 300- 4 600- 600 00 7 - 0 0 9 0 0 - 0 30 IE (M3M7FES) TIME TlttE (MIKUTES) LEGEND* 60 ------CONTROL 89 VISCOSITY (BARBENDER UNIT) 00 3 «00 700- iue 6 mlgah tp 60o ie lu rae o , 61,and for treated flour rice of 6.0 ph at Amylographs - 26 Figure 18 hours with 1.0% acetic anhydride and sodium hydroxide. sodium and anhydride acetic 1.0% with 18hours 0 IE (MINUTES)TIME • D N E G E L CONTROL 90 VISCOSITY (BARBENDER UNIT) iue 7 mlgah a H . frc fortetdfr1 6and 1, for treated flour rice of 6.0 pH at Amylographs - 27 Figure 18 hours with 5.0% acetic anhydride and sodium hydroxide. sodium and anhydride acetic 5.0% with hours 18 200 300 400 0 0 5 00 6 00 7 - 0 30 IE (MINUTES) TIME 60 CONTROL 91 VISCOSITY (BARBENDER UNIT) iue 8 mlgah a p 60o rc for rae o 1,6and for treated flour rice of 6.0 pH at Amylographs - 28 Figure 18 hours with 0.1% succinic anhydrid eand sodium hydroxide. sodium eand anhydrid succinic 0.1% with 18hours 200 300 400- soo 600 700 600 901 - 0 30 IE (MINUTES) TIME LEGEND* 090 60 CONTROL 92 VISCOSITY (BARBENDER UNIT) iue 9 mlgah tp 60o ie lu rae o , 6and 1, for treated flour rice of 6.0 pH at Amylographs - 29 Figure 18 hours with 1.0% succinic anhydride and sodium hydroxide. sodium and anhydride succinic 1.0% with 18hours 200 300 400 500 00 6 700- eoo - 0 30 IE (MINUTES) TIME 60 CONTROL 93 VISCOSITY (BARBHMDER UNIT) iue 0 mlgah a p 60o ie lu tetd o , 6and 1, for treated flour rice of 6.0 pH at Amylographs - 30 Figure 18 hours with 5.0% succinic anhydride and sodium hydroxide. sodium and anhydride succinic 5.0% with 18hours 0 0 2 300-] IOC 400- 500' 600- 700' © 900' 00 -] 0 - 30 IE (MINUTES) TIME ’♦N LEGEND 60 // CONTROL 94 90 VISCOSITY (BARBENDER UNIT) iue 1 mlgah tp 60o ie lu rae fr 1, 6and for treated flour rice of 6.0 pH at Amylographs - 31 Figure 18 hours with 0.1% acetic anhydride and sodium carbonate. sodium and anhydride acetic 0.1% with 18hours 200 300^ 100 50 OH 700- 90CH 0- - - 0 30 IE (MINUTES) TIME 0 4 CONTROL 95 90 VISCOSITY (BARBENDER UNIT) iue 2 mlgah a H . f ie lu rae o 1 6and 1, for treated flour rice of 6.0 pH at Amylographs - 32 Figure 18 hours with 1.0% acetic anhydride and sodium carbonate. sodium and anhydride acetic 1.0% with 18hours 300 400- soo 700 0 30 IE (MINUTES) TIME LEGEND CONTROL 96 VISCOSITY (BARBENDER UNIT) Figure 33 - Amylographs at pH 6.0 of rice flour treated for 1, 6 and 1, 6for treated flour rice of 6.0 pH at Amylographs - 33 Figure 18 hours with 5.0% acetic anhydride and sodium carbonate. sodium and anhydride acetic 5.0% with 18hours 0 0 2 0 0 0 1 300 100 400 500 600 00 7 - 0 - 0 3 IE (MINUTES) TIME 60 CONTROL 97 VISCOSITY (BARBENDER UNIT) iue 4 mlgah a H . frc for rae fr1 6and 1, for treated flour rice of 6.0 pH at Amylographs - 34 Figure 18 hours with 0.1% succinic anhydride and sodium carbonate. sodium and anhydride succinic 0.1% with 18hours 200-1 300- «00 600- 700- OOO- 900-j 0 IE (MINUTES) TIME LEGEND* 60 CONTROL. 98 VISCOSITY (BARBENDER UNIT) iue3 mlgah tp . frc for rae fr , and 6 1, for treated flour rice of 6.0 pH at - 35Amylographs Figure 18 hours with 1.0% succinic anhydride and sodium carbonate . carbonate sodium and anhydride succinic 1.0% with 18hours 200 300 400 500 600 700 900-j - 0 30 IE (MINUTES) TIME LEGEND* 60 CONTROL 99 VISCOSITY (BAFBENDER UNIT) iue 6-Ayorpsa p 60o rc fortetd o 1 6 and 6 1, for treated flour rice of 6.0 pH at 36- Amylographs Figure 18 hours with 5.0% succinic anhydride and sodium carbonate. sodium and anhydride succinic 5.0% with 18hours 200 300- 400- 500- 700 eoo- - 0 IE (MINUTES) TIME 6030 CONTROL 100 90 101 Table 8 - Amylograph viscosities of unmodified and modified rice flours at neutral pH Treatment Gelatinization Peak Viscosity Setback AnhydrideA Alkali Time Temp. Viscosity 30 min, 95 C Viscosity NaOH 1 71 760 380 -60 6 70.4 710 345 +10 18 71.6 870 390 -120 Na„C0Q 1 71.6 745 335 0 Z sj 6 71 730 360 +40 18 73.1* 700 320 -10 0.1% AA NaOH 1 72.8* 780 305 -100 6 71.1 860 390 -60 18 71 855 410 -105 1.0% AA NaOH 1 70.4 780 380 +30 6 72.5* 760 400 +90 18 71 890 410 -60 5.0% AA NaOH 1 73.1* 790 410 +120 6 73.1* 730 350 +60 18 73.1 770 500 +120 0.1% SA NaOH 1 71 590 285 +30 6 71 560 250 -10 18 69.5 650 290 -50 1.0% SA NaOH 1 70.7 590 278 -5 6 71.9* 590 260 -5 18 71.1 630 270 -10 5.0% SA NaOH 1 72.5* 520 250 +60 6 73.4* 550 270 +70 18 73.7* 560 310 +110 0.1% AA Na_C0o 1 70.4 830 390 +40 Z j 6 70.4 820 370 +10 18 71 790 350 -30 1.0% AA Na„C0o 1 75.5* 760 500 +110 Z 6 6 70.4 610 400 +190* 18 71 800 495 -50 5.0% AA NaoC0o 1 75.5* 155* 170 +195* Z J 6 73.4* 540 500 +290* 18 73.4* 810 780 +190* 0.1% SA Na_C0o 1 71 670 290 -50 Z J 6 71 660 310 +40 18 68 625 295 +15 102 Table 8 - Continued 1.0% SA Na2C03 1 71 605 330 +105 6 71 575 420 +205* 18 71 580 350 190* 5.0% SA Na2C03 1 71 530 540 +360* 6 71 565 450 +235* 18 72.5* 495 330 +75 Control (rice flour) 68 820 390 -50 A AA = Acetic Anhydride SA - Succinic Anhydride ♦Significantly different (PC0.05) from the control (unmodified rice flour). 103 Table 9 - Mean values for araylograph viscosity of modified rice flours * Mean Values * Treatment Peak Vise. Viscosity Setback Vise. 30 min, 95 C At Neutral pH+ : Acetic anhydride 740. 56 A 417.22 A 45. 78 A Sucinic anhydride 585. 83 B 321.00 B 75. 83 A Sodium hydroxide 691. 94 A 334.33 A 15. 83 A Sodium carbonate 634. 44 A 403.88 A 117. 78 B 0.1% anhydride 724. 17 A 327.92 A -22. 50 A 1.0% anhydride 680. 83 A 374.42 A 65. 83 A 5.0% anhydride 584. 58 A 405.00 A 157. 08 A At acidic pH: Acetic anhydride 694.39A 112.78A -451. 50 A Succinic anhydride 577. 56 B 97.50 A -367. 38 B Sodium hydroxide 654. 94 A 97.77 A -451. 78 A Sodium carbonate 617. 00 A 112.50 A -367. 11 B 0.1% anhydride 690. 50 A 130.42 A -406. 16 A 1.0% anhydride 646. 33 A 109.17 A -415. 91 A 5.0% anhydride 571. 08 A 75.83 B -406. 25 A + Neutral conditions (pH =6), Acidic conditions (pH =3.5) * Means followed by the same letter do not differ significantly (PC0.05) according to the Least Significant Difference and Duncan's Multiple Range Test. 104 concentration resulted in an increase in the setback viscosity which meant an increase in the rigidity of gel upon cooling. The increase in anhydride concentration caused a decrease in the peak viscosity of rice flours and an increase in the viscosity after 30 rnin at 95°C, although those changes were not significant (P<0.05). Amylograms of flours that had a high ash content corresponding to the high sodium in those samples showed distinctly different amylograms when compared with other flours. The flours with high ash content showed an increase in peak viscosity with the increase in ash content. A typical example is shown in Figure 33, where the flour treated with 5.0% acetic anhydride and sodium carbonate for 1, 6 and 18 hr showed an increase in peak viscosity with the increase in treatment time. No distinct peak was obtained due to the high salt content. The same trend was found in samples treated with 5.0% succinic anhydride and sodium hydroxide, 5.0% succinic anhydride and sodium carbonate. These samples had a high ash content. The effect of high ash content on the amylograms of rice flours was similar to that of salt on the starch amylograms reported by D'Appolonia (1972). The amylograms of those flours that had high ash content would indicate that the high salt causes the starch granules to remain intact for a longer time before fragmentation takes place. It had been reported that c o m starch paste was affected very little during heating with NaCl in concentrations up to 0.1N. At higher concentration of NaCl the peak viscosity increased. The effect of sodium salt on starch viscosity is dependent upon the type of starch. While com starch viscosity increased with sodium chloride and 105 calcium chloride, the viscosity of potato starch decreased with the presence of those salts (Osman, 1967). The same investigator concluded that although the effect of salt on cereal starches is less than that on potato starch, they are sufficient to require consideration in interpretation of changes occurring in starch containing foods. Gelatinization temperature, peak viscosity, viscosity after 30 min at 95°C and the setback of rice flours at neutral pH are presented in Table 8. In general, gelatinization temperatures for modified rice flours were higher than that of unmodified rice flour. Peak heights ranged from 155 to 890 B.U. for modified flours compared to 820 B.U. for unmodified flours. Holding peak viscosity ranged frcm 170 to 780 B.U. for modified flours. While it was 390 B.U. for the unmodified rice flour. The setback viscosity ranged from -105 to 360 B.U. for modified rice flours compared with -50 B.U. for unmodified rice flour. Acidic pH The amylogram of unmodifed rice flour under acidic conditions (pH 3.5) is presented in Figure 37. The viscosity results, that is, peak viscosity and viscosity after 30 min. at 95°C from the amylograph curve were 780 and 105 B.U. with a setback of 470 B.U. (Table 10) for the modified rice flours peak viscosity ranged from 295 to 805 B.U. and viscosity after 30 minutes at 95°C ranged from 35 to 185 B.U. The setback values ranged from -635 to -185 B.U. The behavior of rice flours under acidic conditions was similar to the behavior of other cereal starches under acidic conditions. Anker and Geddes (1944) reported that the maximum viscosity of wheat VISCOSITY (BAPBEHDER UNIT) 0 0 6 00 30 200 400 0 0 5 700 eoo-^ too- iue 7 mlgah t H . fumdfd ie lu (control). flour rice unmodifed of 3.5 pH at Amylograph - 37 Figure ------0 IE (MINUTES) TIME 60 106 90 107 Table 10 - Amylograph viscosities of unmodified and modified rice flours at acidic pH. Treatment Gelatinization Peak Viscosity Setback AnhydrideA Alkali Time Temp. Viscosity 30 min, 95°C Viscosity NaOH 1 68.9 755 80 -560 6 69.5 735 85 -545 18 69.5 715 90 -535 N a oC0., 1 69.5 663 70 -513 z J 6 69.5 683 70 -523 18 69.2 725 80 -545 0.1% AA NaOH 1 68 700 100 -470 6 68 750 115 -508 18 69.2 780 140 -510 1.0% AA NaOH 1 70.4 705 100 -460 6 71 750 170 -430 18 70.4 760 60 -635 5.0% AA NaOH 1 70.4 710 75 -530 6 70.4 643 75 -463 18 70.4 805 150 -520 0.1% SA NaOH 1 67.1 700 100 -480 6 71 543* 115 -283 18 68 600 100 -390 1.0% SA NaOH 1 70.4 598 70 -498 6 68 593 70 -443 18 68 585 110 -415 5.0% SA NaOH 1 69.2 507* 60 -377 6 71 530* 90 -320 18 69.5 530* 60 -400 0.1% AA Na„CO,, 1 70.1 783 170 -373 z J 6 69 780 125 -510 18 70.1 750 185 -345 1.0% AA Na_C0o 1 71 525 185 -315 z -> 6 69.5 580 115 -320 18 70.1 770 115 -515 5.0% AA Na_C0o 1 72.5* 295* 45 -185* z J 6 69.5 518* 65 -428 18 71 695 40 -610 0.1% SA Na„CO^ 1 69.5 650 165 -290 z z 6 68.9 675 150 -350 18 70.1 575 100 -365 108 Table 10 - Continued 1.0% SA Na„CO., 1 69.5 580 120 -295 J 6 69.2 550 90 -340 18 69.8 560 105 -325 5.0% SA Na9C0, 1 72.5* 555 80 -355 J 6 69.5 565 135 -260 18 69.5 500* 35 -427 Control (rice flour) 69.2 780 105 -470 A AA = Acetic Anhydride SA - Succinic Anhydride * Significantly different (P<0.05) from the control 109 starch decreased in linear fashion with the increase in pH. In other words, the decrease in pH produced an increase in the maximum viscosity of wheat starch. Campbell and Briant (1957) reported similar results for the maximum viscosity. They concluded that the increase in citric acid concentration caused the maximum viscosity to become progressively lower but not as low as in the absence of citric acid. The effect of acid on the maximum viscosity was varied due to varietal differences, starch, granule size, as well as the treatment that the starch or flour was subjected to and to the presence of different ingredients like sugars. After reaching the maximum viscosity, the presence of acid caused a drastic lowering of the starch viscosity due to the breakdown of the starch paste. The reduction of paste viscosity was attributed to the disintegration of the amorphous regions of the starch granules and consequent weakening of the granule structure, permitting granule fragmentation with little swelling. The presence of ingredients such as sucrose in the food system has an effect on the viscosity of starch under acidic conditions. Campbell and Briant (1957) reported that increasing the sugar added to the starch paste under acidic conditions resulted in a a thickening effect and higher viscosities were reported with the higher sucrose concentrations. Significant differences (P<0.05) were found among the modified rice flours in their maximum viscosities and their setback viscosities due to the use of acetic anhydrides versus succinic anhydride (Table 9). The effect of sodium carbonate on the setback viscosity was significantly different (PC0.05) from that of sodium hydroxide (Table 9). Only the highest concentration of the anhydride 110 (5% versus 0.1 and 1%) produced a significant difference (PC0.05) in the viscosities of rice flours held at 95°C for 30 min. The behavior of rice flours under acidic conditions are illustrated in Figures 38-51. A slight increase in the maximum viscosity was found in a few amylograms while in the majority of the samples the maximum viscosity was depressed upon lowering the pH to 3.5. The thinning effect of the acid on the viscosity of rice pastes held at 95°C for 30 min was obvious. Modified rice flour pastes varied in their ability to withstand acidic conditions. Some samples were found to have a better resistance to the thinning effect of acid on their paste viscosities as compared with the unmodified rice flour. However, these differences were not significant (PC0.05) (Table 10) . Other samples had a lower viscosity when held at 95°C for 30 min compared with the unmodified rice flour. The setback data showed that acidic conditions resulted in the loss of paste rigidity upon cooling. This is an important characteristic in pie fillings, gravies and other related food products. The results showed that some modified rice flours samples were better when compared to the unmodified rice flour since they had lower setback values which meant that they were less rigid when cooled. Samples with high ash content after modification showed noticably lower maximum viscosities in comparison with the unmodified rice flour maximum viscosity (Figs. 43, 44, 45, 48, 50, 51). Bread Making Bread was made freon modified rice flour in this study to explore the possibility of using this flour in the baking industry. Cross VISCOSITY (BARBENDER UNIT) iue 8 Ayorp a p 35o ie lu tetd o 1 6 and 6 1, for treated tlour rice of 3.5 pH at Amylograph - 38 Figure i8 hours with sodium hydroxide. sodium with i8hours 0 0 2 00 3 0 0 5 00 6 700 i oo- 0------0 30 IE (MINUTES) TIME LEGEND. 60 CONTROL 111 9C VISCOSITY (BARBENDER UNIT) Figure 39 - Amylogrpahs at pH 6.5 of rice flour treated for 1,and 6for treated flour rice of 6.5 pH at Amylogrpahs - 39 Figure 18 hours with sodium sodium carbonate. with 18hours 200 300 500 100- 400 600 70< 00 6 0~ - - 0 30 IE (MINUTES) TIME LEGEND. 60 CONTROL 112 90 Figure 40 - Amylogrpahs at ph 3.5 of rice flour treated for 1, 6and for treated flour rice of 3.5 ph at Amylogrpahs - 40 Figure 18 hours with 0.1% acetic anhydride and sodium hydroxide. sodium and anhydride acetic 0.1% with 18hours VISCOSITY (BARBENDER UNIT) 100 200 300- 500 - 0 0 6 700 600- - 0 060 30 IE (MINUTES) TIME LEGEND CONTROL 113 90 Figure 41 - Amylographs at pH 3.5 of rice flour treated for 1, 6and for treated flour rice of 3.5 pH at Amylographs - 41 Figure VISCOSITY (BARBENDER UNIT) 18 hours with 1.0% acetic anhydride and sodium hydroxide. sodium and anhydride acetic 1.0% with 18hours eoo- 500 600- ?oo- 200 300' 400' ! 00 ' - ' 30 IE (MINUTES) TIME 60 114 90 VISCOSITY (BARBENDER UNIT) iue 2 mlgah a H . frc fortetd o 1 6and 1, for treated flour rice of 3.5 pH at Amylographs - 42 Figure 18 hours with 5.0% acetic anhydride and sodium hydroxide. sodium and anhydride acetic 5.0% with 18hours 200 600- 500' 700- 1 DO- eo o- 00-1 - 0 30 IE (MINUTES) TIME LECEND 60 115 90 VISCOSITY (BARBENDER UNIT) Figure 43 - Amylographs at pH 3.5 of rice flour treated for 1, 6and for treated flour rice of 3.5 pH at Amylographs - 43 Figure 18 hours with 0.1% succinic anhydride and sodium hydroxide. sodium and anhydride succinic 0.1% with 18hours 50C' 600- 300' 700 200 400- 100 - - 0 30 IE (MINUTES) TIME LEGEND. 60 COWTROL 116 90 VISCOSITY (BARBENDER UNIT) iue4 mlgah tp 35o rc for rae fr , and 6 1, for treated flour rice of 3.5 pH at -Amylographs 44 Figure 18 hours with 1.0% succinic anhydride and sodium hydroxide. sodium and anhydride succinic 1.0% with 18hours 6CC-, 700- 300 500- 0 0 2 400- 100 0- - - 30 IE (MINUTES) TIME 60 CONTROL 117 90 VISCOSITY (BARBENDER UNIT) iue4 mlgah t H . f ie lu tetd o 1 6 and 6 1, for treated flour rice of 3.5 pH at -45 Amylographs Figure 18 hours with 5.0% succinic anhydride and sodium hydroxide. sodium and anhydride succinic 5.0% 18with hours 400- - 0 50 600-j 700- 600' 300- 0 0 2 100 - 0 30 IE (MINUTES) TIME LEGEND 60 CONTROL 118 90 VISCOSITY (BARBENDER UNIT) iue4 mlgah tp . frc for rae fr , and 6 1, for treated flour rice of 3.5 pH at -46 Amylographs Figure 18 hours with 0.1% acetic anhydride and sodium carbonate. sodium and anhydride acetic 0.1% with 18hours 200A 100H 300-3 400- 500- 600-3 700-3 BOO- 30 IE (MINUTES) TIME 60 CONTROL 119 VISCOSITY (BARBENDER UNIT) iue4 mlgah tp 35o ie lu tetd o I 6 and 6 I, for treated flour rice of 3.5 pH at - Amylographs 47 Figure 18 hours with 1.0% acetic anhydride and sodium carbonate. sodium and anhydride acetic 1.0% with 18hours 300- 200 - 0 0 5 600- 100- - 0 0 7 - 0 0 6 - 0 30 IE (MINUTES) TIME LEGEND 60 CONTROL 120 90 VISCOSITY (BARBENDER UNIT) iue4 mlgah tp 35 frc fortetd o 1 6 and 6 1, for treated flour rice of 3.5 pH at 48-Amylographs Figure 18 hours with 5.0% acetic anhydride and sodium carbonate. sodium and anhydride acetic 5.0% with 18hours 200 600- 700- 300- 400- 500- 800- too- - 0 30 IE (MINUTES) TIME LECEKD 60 CONTROL 121 VISCOSITY (BARBENDER UNIT) iue 9-Ayorpsa H . o rc for rae fr , and G 1, for treated flour rice of 3.5 pH at 49-Amylographs Figure 18 hours with 0.1? succinic anhydride and sodium carbonate. sodium and anhydride succinic 0.1? with 18hours 0 0 2 300- 500- 600- 100- *oc eoo 0- - 0 30 IE (MINUTES) TIME 60 122 VISCOSITY (BARBENDER UNIT) iue5 mlgah tp 35o ie lu tetd o 1 6 and 6 1, for treated flour rice of 3.5 pH at -50 Amylographs Figure 18 hours with 1.0% succinic anhydride and sodium carbonate. sodium and anhydride succinic 1.0% with 18hours 0 2 300- 600 «00 500 700 60G' 0- ! 0 30 IE (MINUTES) TIME LEGEND 60 CONTROL 123 90 iue 1 mlgaha H . frc for rae fr , and 6 1, for treated flour rice of 3.5 pH at Amylograph - 51 Figure VISCOSITY (BARBENDER UNIT) 18 hours with 5.0% succinic anhydride and sodium carbonate. sodium and anhydride succinic 5.0% with 18hours - 0 0 6 0 0 2 eoon 300- 700' 500' 100- ' 0 30 IE (MINUTES) TIME LEGEND. 60 CONTROL 124 90 125 sections of the bread baked using modified rice flour are presented in Figures 52 to 56. A cross section of rice bread made from unmodified rice flour (control) is presented in Figure 52a. Figures 52 (b-g) represent breads from flour modified with sodium hydroxide and sodium carbonate for 1, 6 and 18 hr. respectively. Breads from flours modified with 0.1%, 1.0% and 5.0% acetic anhydride and sodium hydroxide are presented in Figure 53 (a-i). Succinic anhydride and sodium carbonate effect on bread manufacturing is illustrated in Figure 54 (a-i) where cross sections of bread from flour treated with different concentration of succinic anhydride and for different times are shown. Bread from flour treated with acetic anhydride and sodium carbonate, are shown in Figure 55 (a-i), while bread from flour treated with succinic anhydride and sodium carbonate are shown in Figure 56 (a-i). The cross sections of the different breads illustrates the general appearance of the bread slices, the crumb texture, shape and volume. Differences in the bread volume and the acceptability and quality of the bread will be discussed later in this chapter. In general, breads which had large volume had softer, squeezable crumb which are preferable characteristics of bread. Breads with small volume had a more dense mass, less air cells and of poor quality. Specific Volume Volume is a very important measurement in evaluating bread quality. People prefer bread with spongy texture and relatively large volume. The effect of modification on the specific volume of the breads made from modified rice flours is presented in Table 11. 126 Figure 52 - Cross sections of bread made with modified rice flour. a. No modification (Control) b. Sodium hydroxide for 1 hr'. c. Sodium hydroxide for 6 hr. d. Sodium hydroxide for 18 hr. e. Sodium carbonate for 1 hr. f. Sodium Carbonate for 6 hr. g. Sodium Carbonate for 18 hr. LZV Figure 53 - Cross sections of bread made with modified rice flour. a. 0.1% acetic anhydride and sodium hydroxide for 1 hr. b. 0.1% acetic anhydride and sodium hydroxide for 6 hr. c. 0.1% acetic anhydride and sodium hydroxide for 18 hr. d. 0.1% acetic anhydride and sodium hydroxide for 1 hr. e. 1% acetic anhydride and sodium hydroxide for 6 hr. f. 1% acetic anhydride and sodium hydroxide for 18 hr. g. 5% acetic anhydride and sodium hydroxide for 1 hr. h. 5% acetic anhydride and sodium hydroxide for 6 hr. i. 5% acetic anhydride and sodium hydroxide for 18 hr. 130 Figure 54 - Cross sections of breads made with modified rice flour. a. 0.1% succinic anhydride and sodium hydroxide for 1 hr. b. 0.1% succinic anhydride and sodium hydroxide for 6 hr. c. 0.1% succinic anhydride and sodium hydroxide for 18 hr. d. 1% succinic anhydride and sodium hydroxide for 1 hr. e. 1% succinic anhydride and sodium hydroxide for 6 hr. f . 1% succinic anhydride and sodium hydroxide for 18 hr. g. 5% succinic anhydride and sodium hydroxide for 1 hr. h. 5% succinic anhydride and sodium hydroxide for 6 hr. i. 5% succinic anhydride and sodium hydroxide for 18 hr. 121 132 Figure 55 - Cross section of breads made with modified rice flour. a. 0.1% acetic anhydride and sodium carbonate for 1 hr. b. 0.1% acetic anhydride and sodium carbonate for 6 hr. c. 0.1% acetic anhydride and sodium carbonate for 18 hr. d. 1% acetic anhydride and sodium carbonate for 1 hr. e. 1% acetic anhydride and sodium carbonate for 6 hrs. f. 1% acetic anhydride and sodium carbonate for 18 hr. g. 5% acetic anhydride and sodium carbonate for 1 hr. h. 5% acetic anhydride and sodium carbonate for 6 hr. i. 5% acetic anhydride and sodium carbonate for 18 hr. 133 134 Figure 56 - Cross sections of breads made with modified rice flour. a. 0.1% succinic anhydride and sodium carbonate for 1 hr. b. 0.1% succinic anhydride and sodium carbonate for 6 hr. c. 0.1% succinic anhydride and sodium carbonate for 18 hr d. 1.0% succinic anhydride and sodium carbonate for 1 hr. e. 1.0% succinic anhydride and sodium carbonate for 6 hr. f. 1.0% succinic anhydride and sodium carbonate for 18 hr g- 5.0% succinic anhydride and sodium carbonate for 1 hr. h. 5.0% succinic anhydride and sodium carbonate for 6 hr. i. 5.0% succinic anhydride and sodium carbonate for 18 hr 135 136 The mean for specific volume using sodium carbonate differ significantly (P<0.05) from that using sodium hydroxide. Anydride concentration also influenced the specific volume of breads significantly (P<0.05). The mean values are presented in Table 12. The higher the concentration of the anhydrides, the lower the specific volume of the bread. Here again, the higher amount of sodium associated with the increase in anhydride concentration during modification had an inhibitory affect on the yeast which was used to leavened the bread. The bread volume depended mainly on the action of the yeast to produce carbon dioxide. The presence of sodium at high level inhibited the yeast from producing enough gas to raise the dough causing poor loaf volume. Water Activity Values for water activity (a^) are presented in Table 11. The water activity of bread made from unmodified rice flours was 0.98 while the a of breads made from modified rice flours ranged from 0.95 to 0.99. Usually baking products have a^ value of 0.95 to 0.99. The concentration of anhydrides significantly (P<0.05) influenced the water activiy of the breads. At 1.0% and 5.0% anhydrides concentration, the water activity of breads decreased significantly (P<0.05) in comparison with the water activity at 0.1% anhydride (Table 13) . The reason for this decrease in a was that the w increase in anhydride concentration accompanied by an increase in the alkali used to keep the condition basic during modification. The higher the alkali amount used, the higher amount of sodium that caused the lowering the water activity. 137 Table 11 - Water activity (a^) and specific volume (cc/gm) of rice breads made from modified rice flours Treatment * ______Water Specific AnhydrideA Alkali Time Activity Volume NaOH 1 0.97 1.94 6 0.97 2.07 18 0.97 1.85 N a oC 0 o 1 0.96 1.38 2 j 6 0.95 1.66 18 0.96 1.98 0.1% AA NaOH 1 0.99 1.68 6 0.99 1.72 18 0.95 2.28 1.0% AA NaOH 1 0.96 1.81 6 0.97 1.62 18 0.95 1.59 5.0% AA NaOH 1 0.96 1.45 6 0.93 1.43 18 0.97 1.34 0.1% SA NaOH 1 0.96 2.01 6 0.96 1.82 18 0.98 2.83 1.0% SA Na„C0o 1 0.96 1.65 2 2 6 0.96 2.22 18 0.97 2.33 5.0% SA Na„C0o 1 0.94 1.39 2 J 6 0.98 1.41 18 0.93 1.48 0.1% AA Na_CO-, 1 0.96 1.54 2 o 6 0.99 1.60 18 0.95 2.22 1.0% AA N a oC 0 0 1 0.96 1.71 6 0.93 1.33 18 0.95 1.42 5.0% AA Na_C0o 1 0.92 1.50 2 J 6 0.94 1.60 18 0.94 1.27 138 Table 11 - Continued 0.1% SA Na.CCU 1 0.98 2.25 £. J 6 0.97 1.71 18 0.96 1.47 1.0% SA Na„C0o 1 0.94 1.31 6 0.93 1.49 18 0.97 1.20 5.0% SA Na„C0o 1 0.95 1.66 6 0.94 1.27 18 0.93 1.26 Control (unmodified flour) 0.98 1.77 * No significant differences (P<0.05) were found from the control A AA = Acetic anhydride SA = Succinic anhydride 139 Table 12 ~ The effect of anhydrides concentration and type of alkali on the specific volume of rice breads Treatment Mean Specific Volume Sodium hydroxide 1.78 A* Sodium carbonate 1.54 B 0.1% anhydride 1.93 A 1.0% anhydride 1.64 B 5.0% anhydride 1.42 B k Means followed by the same letter are not significantly different (P<0.05) according to the Least Significant Difference and Duncan's Multiple Range Test. 140 Table 13 - The effect of anhydrides concentration on the water activity of breads made from modified rice flours Treatment Mean Water Activity 0.1% anhydride 0.97 A* 1.0% anhydride 0.95 B 5.0% anhydride 0.94 B * Means not followed by the same letter are not significantly different (P<0.05) according to the Least Significant Difference and Duncan's Multiple Range Test. 141 Texture Analysis Texture analysis results from breads made from modified rice flours are presented in Table 14. The shear press value (pH/w) ranged from 0.197 to 0.510 (newton/g) compared to 0.374 for the bread made from unmodified rice flour (control). The results revealed that some samples required more force than others. The bread made from rice flour modified with 0.1% acetic anhydride and sodium carbonate for 18 hr required the highest force applied. That modified with 5.0% acetic anhydride and sodium carbonate required the lowest force. The bread which received the lowest force had a brittle, loose texture resembling the texture of cake rather than bread. In comparing the breads from modified rice flours with the control, no significant differences were found in the shear press values (PC0.05). Significant differences (PC0.05) resulted in the shear press values due to the use of acetic anhydride versus succinic anhydride (Table 15). The anhydride concentration also significantly (PC0.05) affected the shear press values (Table 15). The results showed that with the increase in anhydride concentration the force required to shear the bread slices decreased. Table 16 shows a significant effect of alkali type at different anhydrides concentrations. The results illustrated graphically in Figure 57 show that the force required for shearing slice decreased with the increase in anhydride concentration using sodium carbonate and sodium hydroxide to provide the alkali conditions. However, using 0.1% anhydride with sodium carbonate required the highest force to sheer the bread 142 Table 14 - Texture analysis of rice bread Treatment Sheer press Compressability AnhydrideA Alkali Time pH/W (newton/gm) E. Modulus (newton/M ) NaOH 1 0.290 3338.69 6 0.395 3407.33 18 0.290 3514.59 N a oC0 o 1 0.255 3510.44 £■ 3 6 0.372 3486.25 18 0.289 3601.71 0.1% AA NaOH 1 0.292 3447.23 6 0.331 3526.20 18 0.260 3865.92 1.0% AA NaOH 1 0.373 2013.86 6 0.230 3500.12 18 0.370 2483.48 5.0% AA NaOH 1 0.295 3577.51 6 0.315 3574.47 18 0.297 3555.81 0.1% SA NaOH 1 0.263 3609.03 6 0.297 3589.75 18 0.296 3187.34 1.0% SA NaOH 1 0.250 3554.82 6 0.260 3756.93 18 0.265 3457.93 5.0% SA NaOH 1 0.211 3647.12 6 0.202 3554.98 18 0.217 3506.31 0.1% AA Na„C0o 1 0.318 3475.39 2 3 6 0.407 3664.96 18 0.510 3666.88 1.0% AA Na„C0o 1 0.288 3633.10 6 0.277 3542.68 18 0.282 3522.59 5.0% SA Na„C0o 1 0.197 3668.72 6 0.306 3554.47 18 0.287 3572.50 0.1% SA Na„CO, 1 0.330 3577.03 2 3 6 0.396 3199.03 18 0.274 3562.75 143 Table 14 -- Continued 1.0% SA Na„CO_ 1 0.290 3451.98 6 0.280 3565.16 18 0.280 3500.27 5.0% SA N a oC 0 o 1 0.191 3579.98 6 0.211 3683.34 18 0.212 3531.39 control 0.374 3641.30 * Significantly different (PC0.05) from the control A AA = Acetic Anhydride SA = Succinic Anhydride 144 Table 15 - Mean value for sheer press (pH/W) for modified rice breads as influenced by the anhydride type and their concentrations * Treatment Means Acetic anhydride 0.313A Succinic anhydride 0.263B 0.1% anhydride 0.331A 1.0% anhydride 0.287 B 5.0% anhydride 0.245 C * Means followed by the same letter do not differ significantly (P<0.05) according to the Least Significnat Differences and Duncan's Multiple Range Test. 145 Table 16 - Sheer press values as influenced by the alkali type at different anhydrides concentrations •k Treatment Means 0.1% anhydride + sodium carbonate 0.372 B 1.0% anhydride + sodium carbonate 0.283 A 5.0% anhydride + sodium carbonate 0.234 A 0.1% anhydride + sodium hydroxide 0.290 A 1.0% anhydride + sodium hydroxide 0.291 A 5.0% anhydride + sodium hydroxide 0.256 A * Means followed by the same letter do not differ significantly (P<0.05) according to the Least Significant Difference and Duncan's Multiple Range Test. ifrn ahdie cnetain o te oc rqre t shear to requried force the at on hydroxide sodium concentrations versus carbonate anhydrides sodium of effect different The - 57 Figure the bread slices. bread the PEAK HIGHT/SAMPLE WEIGHT 0 0 0 0.23- 0.25- 0.27 0.29- 0.30- 0.32 0.33- 0.35- 0.36- 0.37 . . . 0 2 21 22 - - - 0.1 CXJNCENTRATION OF ANHYDRIDE OF CXJNCENTRATION OrJ HYDROXIDESOOriJM CIH CARBONATE SCOIUH 5.0 146 147 slices. The canpressability results revealed no significant differences among breads due to the use of alkali, anhydride type concentration, and modification time. Elasticity modulus 2 (newton/m ) for breads made from modified rice flours ranged from 2013.86 to 3865.20 compared to 3641.30 for rice bread made from unmodified rice flour (control). In general, modification of rice flour caused a decrease in the force required to compress the bread slices as compared to the control and reflected an increase in bread softness. The increase in the bread softness (squeezability) may be due to tiie fact that modification resulted in an increase in the bread volume for several samples. As the volume increases, the bread will have more air cells which gives the bread the preferable squeezable characteristics. Canpressability and softness of bread is affected by different factors. In a study done by Platt and Powers (1940), it was reported that canpressability increased due to the increase in shortening, skim milk solids and sugar added to the flour prior to bread making. They indicated that proper mixing, optimum fermentation and the degree of baking also increased the softness of the bread crumb. Staling of bread decreased the compressability drastically during storage. Maleki et al. (1980) concluded that the decrease in baking time increases the moisture content in the bread and resulted in softer bread after baking and during storage for 3 days. Protein content also influenced bread softness, the higher the protein content the softer the bread produced. 148 Electron Microscopy of Rice Flours and Rice Breads Scanning electron micrographs of the unmodified and modified rice flours are shown in Figure 58. The micrographs of the unmodified rice flour show large irregular starch granules with some protein bodies. In comparison with the unmodified flour, modified flours showed the starch granules with an angular (generally five-sided) surface. The starch granules were more aggregated into clusters than the granules of unmodified rice flours (Figs. 58b, 58c). Modification of rice flour with acetic anhydride and succinic anhydried are shown in Figures 58b and 58c, respectively. Modification with succinic anhydride appeared to affect the surface of the starch granules in giving them rougher surface as compared with acetic anhydride. The shape of modified rice flour starch granules was similar to that of rice starch reported by Fitt and Snyder (1984). However, the starch granules shape of the modified rice flour had a more angular shape with sharper edges. Micrographs of wheat bread (ccmmercially made) and rice bread made from unmodified rice flour are presented in Figures 59a and 59b. The wheat bread micrograph showed that the gluten which is responsible for the elastic and extensible properties of the bread dough formed a smooth surface with the starch granules were embedded inside the dough. The smooth, sticky and uncracked surface which is elastic and extensible gives the dough the ability to retain gas and produce bread with a good volume. In comparison, unmodified rice bread had a rough surface with starch granules projecting out from the surface. This reflects the fact that rice dough lacks the 149 Figure 58. Scanning electron micrographs of a) Unmodified rice flour; b) Modified rice flour with 1% acetic anhydride in sodium hydroxide for 6 hr; c) Modified rice flours with 1% succinic anhydride in sodium hydroxide for 6 hr. 091- 151 Figure 59 - Scanning electron micrographs of a) Rice bread; b) Wheat bread; c) Rice bread made from rice flour modified for 6 hr with sodium hydroxide; d) Rice bread made fran rice flour modified for 6 hr with sodium carbonate. Z21 153 protein glutin. The use of methylcellulose in rice bread formulation helped the dough to retain the gas to some extent, however, the breads had small volume and a very dense texture as compared with wheat bread. Micrographs of rice breads modified with sodium hydroxide and sodium carbonate are presented in Figures 59c and 59d. The starch granules were lined up on the crumb surface and were not enmeshed within it. These crumbs lacked elasticity and the loaves were of poor volume. The clear cut cracks and the small holes serves as an indication of the lack of elasticity and extensibility of the dough. Rice bread made from rice flour treated with acetic anhydride and sodium hydroxide are shown in Figures 61a, 60a and 60b. At 5.0% acetic acid concentration, bread crumb had smoother surface where most of the starch granules embedded within the surface. Figure 61 (a,b,c and d) shows the effect of 0.1% acetic anhydride versus 0.1% succinic anhydride with the use of sodium hydroxide versus sodium carbonate as an alkali medium. In general, it appeared that succinic anhydride gave more stickiness to the bread dough in comparison with acetic anhydride. The effect of different concentrations of succinic anhydride with sodium hydroxide is illustrated in Figures 61b and 62a. Surface smoothness and stickiness increased with the increase in the concentration of succinic anhydride. The use of different concentrations of succinic anhydride with sodium carbonate is llustrated in Figures 61b, 62b and 62c. Here again, the increase in succinic anhydride concentration caused an increase in smoothness of the crumb surface and in different 154 Figure 60 - Rice bread made from rice flour modified for 6 hr with a) 1% acetic anhydride and sodium hydroxide; b) 5% acetic anhydride and sodium hydroxide. 991 156 Figure 61 - Rice bread made fran rice flour modified for 6 hr with a) 0.1% acetic anhydride and sodium hydroxide; b) 0.1% succinic anhydride and sodium hydoxide; c) 0.1% succinic anhydride and sodium carbonate; d) 0.1% acetic anhydride and sodium carbonate. 157 158 Figure 62 - Rice bread made from rice flour modified for 6 hr with a) 1% succinic anhydride and sodium hydroxide; b) 1% succinic anhydide and sodium carbonate; c) 5% succinic anhydride and sodium carbonate. 6SI- 160 treatments did not result in a large volume with an acceptable bread all the time. Some breads with smooth surfaces were rejected by the taste panel or had a low total score. The poor volume and the poor quality of those breads could be attributed to the high amount of electrolytes (mainly sodium). Sodium inhibited the growth of yeast and prohibited production of carbon dioxide, which gives rise to the bread dough. Also, the high sodium content made those breads unpalatable. Sensory Evaluation Loaves of bread made from modified rice flours were evaluated by a trained taste panel. The results are presented in Table 17. The results showed that volume of bread slices varied among the different breads as compared with the bread from unmodified rice flour (control) . Some breads made from modified rice flour had very high scores. Volume scores ranged from 4.90 to 9.72 (max. score = 10) compared to 5.78 for the bread made with unmodified rice bread. The large volume is preferable by consumers. This characteristic is one of the most important parameters that bread quality is based on. Few samples had very low scores. The use of sodium hydroxide alone resulted in breads that had larger volume as compared with breads made from flours treated with sodium carbonate. Breads made frcm modified rice flour that had high ash content had small volume and inferior quality. In addition, seme breads were discarded and not examined by the taste panel due to the very harsh and unpleasant taste of those bread. The unpalatabi1ity of those breads may be attributed to the fact that they were made 161 Table 17 - Sensory evaluation scores for bread made from modified rice flours Treatment AnhydrideA Alkali Time Volume Grain Taste Texture Total NaOH 1 8.28 7.78 11.39 10.89 76.44 6 7.42 8.55 12.50 12.4 83.17 18 7.83 8.21 12.44 12.00 80.19 1 5.72 7.91 9.28 9.22 64.40 Na„C0oA J 6 5.83 8.22 11.33 10.55 74.39 18 6.89 7.72 12.55 13.33 80.16 0.1% AA NaOH 1 6.75 8.03 11.92 12.11 78.80 6 5.80 7.75 11.83 11.5 74.86 18 8.28 7.55 12.61 12.94 82.30 1.0% AA NaOH 1 7.03 8.32 12.28 11.94 82.26 6 7.41 9.01 13.08 12.17 82.60 18 6.94 8.69 12.11 11.61 80.82 5.0% AA NaOH 1 6.47 7.82 11.00 10.67 75.82 6 4.92 7.52 10.05 9.72 68.33 18 5.69 7.83 10.61 10.47 71.05 0.1% SA NaOH 1 9.31 8.6 13.00 13.72 88.61 6 9.39 8.28 12.00 13.55 85.90 18 9.14 7.83 13.75 14.14 89.24 1.0% SA NaOH 1 7.01 7.83 10.67 11.72 77.26 6 9.72 8.11 13.28 14.28 89.45 18 9.44 8.51 12.97 13,94 90.01 0.1% SA Na_CO- 1 6.19 8.01 11.33 10.44 74.24 6 5.61 7.68 10.72 9.58 71.65 18 7.50 7.65 11.05 11.5 77.35 1.0% AA Na_C0o 1 7.12 7.33 11.00 10.97 74.41 b *5 18 5.89 7.89 10.61 10.72 73.37 0.1% SA Na_C0o 1 8.75 7.91 12.50 13.11 84.49 Z J 6 7.75 7.83 12.27 11.90 82.53 1.0% SA Na_C0o 6 5.11 7.72 7.78 8.53 63.02 2 o Control (unmodified flour) 5.78 8.30 12.03 10.78 77.60 A AA = Acetic Anhydride, SA = Succinic Anhydride 162 with flours that had a very high ash content. The highest volume score was given to the bread made from flour modified with 1.0% succinic anhydride and sodium hydroxide for 6 hr, while the bread made with flour modified with 1.0% succinic anhydride and sodium carbonate for 6 hr received the lowest score. Differences in volume scores were not significant (P<0.05). Bread crumb grain score varied among different breads with the highest score of 9.01 (maximum score = 10) given for bread made from flour modified with 1.0% acetic anhydride and sodium hydroxide for 6 hrs. The lowest score (7.33) was given to bread made from flour treated with 1.0% acetic anhydride and sodium carbonate for 1 hr. Significant differences (P<0.05) were found among the crumb grain score due to the use of sodium hydroxide versus sodium carbonate (Table 18). The effect of acetic anhydride versus succinic anhydride and the different anhydrides concentrations are illustrated in Figure 63. These were not significant (P<0.05). A significant (PC0.05) effect of alkali at different concentrations of anhydrides was found. Table 19 shows the mean values for the grain scores and the effect of alkali in different anhydrides concentrations. These results are illustrated graphically in Figure 64. The results revealed that at lower concentrations of anhydrides (0.1% and 1.0% versus 5.0%) the grain scores were higher. In addition, the grain scores were higher for breads when sodium hydroxide was used in comparison with sodium carbonate. The anhydride concentration and time of modification interacted and significantly affected the grain scores. The results are presented in Table 20 and illustrated graphically in Figure 65. 163 Table 18 - Effect of rice flour modification on the sensory characteristics or rice bread * Treatment Means Taste Sodium hydroxide 12.08 A Sodium carbonate 10.93 B Texture Sodium hydroxide 12.30 A Sodium carbonate 11.08 B Grain Sodium hydroxide 8.11 A Sodium carbonate 7.72 B Total Score Sodium hydroxide 81.15 A Sodium carbonate 75.79 B Means not followed by the same letter do not differ significantly (P<0.05) according to the Least Significant Difference and Duncan's Multiple Range Test. Figure 63 - The effect of anhydride modification of rice flour bread flour rice of modification anhydride of effect The - 63 Figure crumb grain scores. grain crumb BREAD GRAIN SCORE 7.65- 7.68- 7.71- 7.77 7.83 7.92- 8.0 0.1 CONCENTRATION OF ANHYDRIDE OF CONCENTRATION ♦ SUCCINIC ANHYDRIDE ♦ SUCCINIC ACETIC ANHYDRIDE 5.0 164 165 Table 19 - Effect of alkali in different concentrations of the anhydrides on the grain score of bread crumb * Treatment Means 0.1% anhydride + sodium hydroxide 8.01 B 1.0% anhydride + sodium hydroxide 8.41 A 5.0% anhydride + sodium hydroxide 7.73 B 0.1% anhydride + sodium carbonate 7.76 B 1.0% anhydride + sodium carbonate 7.65 B * Means have the same letter do not differ significantly (P<0.05) according to the Least Significant Difference and Duncan's Multiple Range Test. iue 4 Te fet f lai n ifrn cnetain of concentrations different in alkali of effect The - 64 Figure anhydride on the bread grain scores. grain bread the on anhydride BREAD GRAIN SCORE 7 7.7- 7.5^ 7.8- 9 . 7 8 8 8 8 . . . . . 6 0 2 3 5 ^ ^ - - - 0.1 1.0 CONCENTRATION OF ANHYDRIDE OF CONCENTRATION LEGQ'ID: SODIUM HYDROXIDE SODIUM CARBONATE 5.0 166 167 Table 20 - Effect of anhydrides concentrations at different modification times on the grain score of bread crumb " k Treatment Means 0.1% anhydride for 1 hr. 8.08 ABC 0.1% anhydride for 6 hr s. 7.85 ABC 0.1% anhydride for 18 hrs. 7.50 C 1.0% anhydride for 1 hr. 7.70 ABC 1.0% anhydridefor6 hr s. 8.13 AB 1.0% anhydride for 18 hrs. 8.25 A 5.0% anhydride for 1 hr. 7.82 ABC 5.0% anhydride for 6 hrs. 7.53 A C 5.0% anhydride for 18 hrs. 7.83 ABC * Means with the same letters are not significantly different (PC0.05) according to the Least Significnat Difference modification times on the bread crumb grain score. grain crumb bread the on times modification iue 5 Te fet f nyrd cnetain t different at concentration anhydride of effect The - 65 Figure BREAD GRAIN SCORE 7.5- 7.6- 7.7- 7. 6*7. - o . e e .2 0.1 CONCENTRATION OF ANHYDRIDE OF CONCENTRATION LEGEND hr h 1 r h 8 l a - B - » r h 6 5.0 168 169 Using 0.1% anhydride for 18 hrs, resulted in the lowest grain score, where as, the use of 1.0% anhydride for 18 hrs. resulted in the highest grain score. Bread taste scores are presented in Table 17. The highest score was given to bread made from flour modified with 0.1% succinic anhydride and sodium hydroxide for 18 hr. The lowest score was for bread frcrn flour modified with 1.0% succinic anhydride and sodium carbonate for 6 hr. The use of sodium carbonate to bring about basic conditions during modification adversely influenced the taste scores (P<0.05) in comparison with sodium hydroxide. The mean scores are presented in Table 18. Significant differences (P<0.05) were found in the bread texture scores due to the use of sodium carbonate versus sodium hydroxide (Table 18) . The texture scores for the different breads from modified rice flours are presented in Table 17. The scores ranged from 8.53 to 14.28 (maximum score = 15) . The texture score for the control bread was 10.78. The total scores for breads made with modified flour ranged from 63.02 to 90.01 (maximum score = 100). The total score of the control bread was 77.60 (Table 17) . Significant differences (PC0.05) among the total scores for breads were found due to the use of sodium carbonate versus sodium hydroxide (Table 18) . The effect of alkali type at different anhydride concentrations was significant (P<0.05), the results are presented in Table 21 and illustrated graphically in Figure 66. The results showed that low anhydride concentrations (0.1% and 1.0% versus 5.0%) resulted in higher total scores when sodium hydroxide was used to provide the basic conditions during 170 Table 21 - Effect of alkali in different anhydrides concentration of the total score for rice bread * Treatment Means 0.1% anhydride + sodium hydroxide 83.29 A 1.0% anhydride + sodium hydroxide 83.75 A 5.0% anhydride + sodium hydroxide 71.73 AB 0.1% anhydride + sodium carbonate 79.08 AB 1.0% anhydride + sodium carbonate 70.27 C * Means with the same letters are not significantly different (P<0.05) according to the Least Significant Difference and Duncan's Muptiple Range Test. iue 6 Te fet f lai t ifrn cnetain of concentrations different at alkali of effect The - 66 Figure anhydrides on the total score of rice bread. rice of score total the on anhydrides BREAD TOTAL SCORE 70 71 72 73 74 75 76 77 78 80 81 82 83 79 0.1 CONCENTRATION OF ANHYDRIDE OF CONCENTRATION 1.0 SODIUM GXRBONATE♦ LEGEND: SODIUM HYDROXIDE 5.0 172 modifications. The results also revealed that the use of sodium carbonate resulted in lower total scores in comparison with the use of sodium hydroxide. In general, the taste panel evaluations revealed that a high quality bread can be produced from modified rice flour. Some modification resulted in a very good quality breads, others resulted in an inferior quality bread. The factor that caused the low scores and poor quality of those breads was the high ash content of these breads. As previously discussed, the increase in ash content adversely influenced the bread volume. The high ash also caused a harsh taste and tendered seme breads unpalatable. The breads made from flour modified with 5.0% anhydride flour, especially when sodium carbonate was used, produced the most unacceptable breads. The high concentration of anhydride during modification along with the addition of high amounts of sodium carbonate causes an increase in the ash content in the modified flours. Bread characteristics cure influenced by different factors. The flour type, composition of flour, flour treatments and ingredients added to the flour during dough making are very important in determining the quality and acceptability of bread in addition to the procedures and conditions of baking (Shopmeyer, 1960) . As in the bread made from 100% rice flour, additional factors can also affect the quality of the bread produced. Nishita et al (1976) reported that volume of rice bread was influenced by many factors. The type and amount of methylcellulose added (usually added to enhance air entrapment into the dough), amount of water used to make the dough, type of gums used and the type of shortening influenced the quality of rice bread. In 173 another study, Nishita and Bean (1979) concluded that rice bread is affected by physiocochemical properties of rice used in production of the bread. They reported that although all types of rice can produce bread of similar appearance, the rice with low amylose content and low amylograph viscosity produced breads with superior crumb characteristics. Sll®*ARY AND CONCLUSIONS The objectives of this study were: 1) to investigate the possibility of increasing or altering the functional properties of rice through chemical modification, as a means to increase its utilization in the food industry; 2) to provide new products for those who require special diets free from wheat and related cereals and 3) to provide products such as bread for countries that have to import wehat for bread manufacturing. Proximate analysis of modified rice flour revealed significant differences in the amount of fat was found between flours treated with acetic anhydride versus succinic anhydride. Few samples were significantly different in their crude fat content. As compared with the unmodified rice flour (control). The ash content of modified rice flour was higher than that of the control especially for those treated with 5.0% anhydride. Alkali type and the different anhydride concentrations affected the ash content of modified rice flour. The type and concentration of anhydrides also influenced the ash content, in addition to the influence of alkali type and anhydride concentration. The increase in ash content was due to the use of sodium hydroxide and sodium carbonate during modification. Differences were found in the protein content between flours treated with acetic anhydride versus succinic anhydride and between those treated with sodium hydroxide versus sodium carbonate. The effect of alkali at different concentration of anhydride was significant on the protein content of modified rice flours. 174 175 Modification of rice flour resulted in an increase in the total color and chromaticity differences. Differences were found due to the use of acetic versus succinic anhydride. Alkali type at different anhydride concentrations also influenced the color and chromaticity of rice flour. With the increase in anhydride, the total color and chromaticity difference from the control increased, sodium carbonate resulted in more darkening of rice flour color as compared with sodium hydroxide. Modification increased the clarity of rice flour solutions. Sodium hydroxide was more effective in increasing flour slurries clarity than sodium carbonate. Amylograms of modified rice flours showed that modification influences the behaviour of rice flour. Differences were found in the peak viscosities of flours treated with acetic versus succinic anhydride. Differences were found in the setback between floors treated with sodium hydroxide versus sodium carbonate. The setback viscosity was also influenced by the anhydride concentrations. At acidic pH modifications resulted in a better resistance of rice flour under low pH in comparison with the control. Anhydride concentration, types and alkali type influenced the setback visocities. Bread with a very good overall quality was produced with modified flours. However, some modifications resulted in an inferior quality bread mainly due to the high ash content rather than the modifications. The breads had larger volume, softer squeezable crumb, good taste and lower water activity than the control. 176 Electron micrographs of rice flour and bread showed noticable alteration of their ultrastructure due to the modification with anhydrides and alkali. The structure of seme rice breads resembled that of wheat bread. The use of chemical modifiers on rice flours can change the functional properties of rice flours in a way that can increase the use of rice in such products of breads and possibly other bakery products such as cakes and crackers and also in starch based products such as pie fillings or puddings. 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Criteria of rice quality. In: "Rice Chemistry and Technology." D.F. Houston (Ed). American Assoc, of Cereal Chem., Inc., St. Paul, MN. Whistler, R.L. and G.E Paschall. 1967. "Starch Chemistry and Technology. II." Academic Press, New York. Wolff, I.A., D.W. Olds and G.E. Hilbert. 1951. The acetylation of c o m starch, amylase and amylopectin. J. Amer. Chem. Soc. 73:346. Young, D.J. 1940. U.S. Patent 2,221.563c. VITA Samir Sideek Alhusaini was b om to Mr. and Mrs. Sideek K. Alhusaini, on July 1, 1951 in Mosul, Iraq where he attended primary school. He completed his secondary school in Baghdad. Upon completion of his secondary school in 1968, he was admitted to the University of Baghdad, College of Agriculture in Baghdad, Iraq. In 1972 he received a Bachelor of Science degree in Food Science. The author then spent 4 years at the Higher Institute of Agricultural Technology as assistant lecturer and then he was admitted to the University of Colorado in Fort Collins, Colorado. He received his Master of Science degree in Food Science in May, 1979. He enrolled at Washington State University at Pullman, Washington until 1982. Then he transferred to Louisiana State University in the Department of Food Science where he is a candidate for a Ph.D. degree in Food Science. 189 DOCTORAL EXAMINATION AND DISSERTATION REPORT Candidate: Samir Sideek Alhusaini Major Field: Food Science Title of Dissertation: Modification of Rice Flour and Its Potential Use in the Food Industry Approved: ajor Professor and Chairman A 6r Dean of the Graduate School EXAMINING COMMITTEE: Date of Examination: April 17, 1985