/
MELT TRANSFORMATION EXTRUSION OF SOY PROTEIN; /'
A Thesis Presented to The Faculty of the College of Engineering and Technology Ohio University
In Partial Fulfillment of the Requirement for the Degree Master of Science
by Corry S. Hendrowarsito ;;:;' November, 1984
OHIO UNIVERSITY LIBRARY Acknowledgements
The author wishes to express her appreciation to Professor John R. Collier, without whose guidance and counsel this study could have not been possible. Thanks is al so extended to the facul ty of the Department of Cherni cal Engineering for their advice and help. Special thanks is also due to Indro Subowo, whose help and patience were invaluable. Finally, thanks is due to my parents and brothers whose support were unlimited.
i ABSTRACT
Hendrowarsito, Corry Suzannadevi. M.S. November 1984. Chemical Engineering Director of Thesis: Dr. John R. Collier Title: Melt Transfor.ation Extrusion of Soy Protein (pp. 104, 42 figures, 12 tables)
The purpose of thi s research was to apply the ~1el t Transformation Extrusion Process to the extrusion of soy protein. As a result, an improved layered fibrous texture occurs in soy protein extrudates. Commercially, fibrous soy protein products are used as meat extenders and substitutes. The premoist soy protein was extruded in a system consisting of 3/4 1t - d i a met e r Brabender single screw extruder, an eighteen inch conditioner zone, and a uniaxial die having a deformation ratio of 24:1, 1/16 11 x 1/2 11 ribbons were produced. Variables studied included oC), process temperature profile (160-90 screw speed (40-80
RPt4) and moisture content (30-40%). The effect of these variables on die pressure, absorption, bulk density, product temperature, and extruder throughput was investigated using response surface analysis. Studies using optical and scanning electron microscopy were conducted to examine the product structure.
i i The r~TE process produced higher pressure drops (300-1500 psi) and longer residence times (5-15 minutes) compared to the more conventional low pressure extrusion (less than 500 psi). Control of both shear rate or stress, and temperature profile were found to be the most important factors. Product temperature and operating pressure were significantly
affected by screw speed. Shear rate or stress, and pressure decreased with increasing moisture. The best operating conditions for maximum texturization . 0 0 0 0 were a temperature pr o f t l e of 160 -135 -110 -50 C, 80 RPM, and 40% moisture. Differential scanning calorimetry was employed to determine the crystallinity of the dough. The result indicated that DSC was not an appropriate method. Scanning electron microscopy displayed clearly the physical changes which occurred due to process conditions.
iii Table of Contents
Page
List of Figures vi
List of Tables .. i x Chapter
1 . Introduction 1
2. Background of Study .. 4 2.1 Protein 6
2.2 Soy Protein and Its Commercial Use 8
2 • 3 Mechanism of Fiber Formation. 11
3. Theory 16 3.1 Melt Transformation Extrusion Process (MTE) ••••••• 16 3.1.1 Shear Stress and Flow Induced Crystallization ...... 17
3.1.2 Pressure Effect on Crystallization 21
3.2 Extrusion Cooking 24 3.3 Characteristics of Textured Protein Prod uc ts ...•...•... 28
3.4 Response Surface Analysis (RSA) 29 4. Description of Equipment and Material 31
5 • Experimental Procedure 40
5.1 Preliminary Experimentation 41
5.2 Experimentation 45
5.3 Specimen Testings 47
i v Chapter Page
6. Results ...... •. 50
7. Discussion ... 74
8. Conclusion ....•.•.. 87
9. Recommendation ... 89
Bi bl t ography •...... •. 91 Appendixes
A. Experimental Data •.•••••• 97
B. Response Surface Analysis Program 101
C. Response Surface Analysis Results 102
v list of Figures
Figure Page
1. Mechanism of Protein Denaturation. 12
2 . Structure of Spherulite . 18
3 . Su99ested i~ 0 del for Fibe r Format ion • 18
4. Elongational Flow in a Converging Die .. 20 5 . Nematic Liquid Crystalline Form. 22 6. Cross Section of a Typical Food Extruder. 25
7. Sc he (0a tic Di a gram for the Un i a x i a 1- rib bon Die 33
8 . Schematic Diagram for the Fiber Die 34
9 . Photograph of Uniaxial Die Halves. 35
10. Photograph of Fiber Die Pieces ..• 35 11. Schematic Diagram for the Extrusion Process with a Melt Conditioner Zone . . . 38 12 . Front View of the Extrusion Set-up 39
13 . Simplified Extrusion Flow Sheet 45 14. Extrusion Rate versus Screw Speed at different Moisture Contents ... 52 15. Extrusion Rate versus Screw Speed at different Process Temperature. 53 16. The Effect of Screw Speed and Moisture on the Extrusion Rate at 8 Constant Processing Temperature of 150 C (zone II). •..• 54 17. The Effect of Processing Temperature and Moisture on Extrusion Rate at a Constant Screw Speed of 70 RPM ••..••.... 55
vi Figure Page
18. Die Pressure versus Screw Speed at different Processing Temperatures · · · . ... · . . 56 19 . Die Pressure versus Screw Speed at different Noisture Contents . . . · · · · . . 57 20. Die Pressure versus Screw Speed for the Fiber Die Runs ...... · · · . . · 59 21. The Effect of Screw Speed and Moisture on the Die Pressure at a COBstant Processing Temperature of 152.8 C (zone II). . . . 60 22. The Effect of Temperature and Moisture on the Die Pressure at a Constant Screw Speed of 45 RPM •••• •• •••••• 61 23. The Effect of Temperature and Screw Speed on the Die Pressure at a Constant Moisture Content of 40 w/o •••••••.••• 62
24. DSC Endotherm for Indium 63 25. Typical DSC Endotherm of Texturized Soy Protein Product ...... •.. 64 26. The Effect of Temperature and Moisture on the Product Absorption at a Constant Moisture Content of 35 wlo ...... 65 27. The Effect of Temperature and Moisture on the Product Absorption at a Constant Screw Speed of 70 RPM ••• •••••• 66 28. The Effect of Screw Speed and Moisture on the Product Absorptionoat a Constant Processing Temperature of 150 C (zone II) .•.• 67 29. The Effect of Temperature and Screw Speed on the Product Bulk Density at a Constant Moisture Content of 35 w/o • • • • • • 69 30. The Effect of Temperature and Moisture on the Product Bulk Density at a Constant Screw Speed of 76 RPM •...•..•.•••. 70
v; i Figure Page 31. The Effect of Temperature and Screw Speed on the Product Temperature at a Constant Moisture Content of 27 wlo ...... 71 32. The Effect of Temperature and Moisture on the Product Temperature at a Constant Screw Speed of 135 RPM . .. 72 33. The Effect of Temperature and Moisture on the Product Temperature at a Constant Process- ing Temperature of 140°C (zone II) .... 73 34. Optical Micrograph of Fiber Die Runs, 12X .. 77 35. Scanning Electron Micrograph of Run F4 shows porous structure, 700X ...... 77 36. Processing Temperature Profile at different Heating Zones...... 81
37. Residence Time versus Screw Speed 83 38. Scanning Electron Micrograph of Untexturized Soy Protein with Strands of Fibers, lOOOX. 84 39. Optical Microscope of Fibrous Structure of Run F3, 150X ...... • . . . .. 84 40. Scanning Electron Micrograph of Isolated Fiber of Run F3, 4000x ...... 86 41. Scanning Electron Micrograph of Run 13, lOOOX 86
42. SAS Program .•. 101
vii i list of Tables
Table Page 1. Extruded versus Spun Texturizing Ingredients 5
2 • Typical Composition of Soy Flours, Concentrates and Isolates 9
3. Amino Acid Composition 9 4. Changes in Characteristics of Soybean Protein at High Temperature Heating...... 15 5. Experimental Pattern of Processing Condition Code s...... 44
6. Effects of Variables on Extrudate Character- istics ...... 75
7. Die Temperatures 97
8. Flow Rates ..... 98
9 • Pressure Profiles. 99 10. Extrusion characteristics 100 11 . Regression Coefficients. 102 12. Analysis of Variance 103 13. Levels of Variables Significance on Extrudate Characteri sti cs •...•.•..••• •• 104
ix Chapter 1 INTRODUCTION
The texturization of vegetable protein products to simulate meat has been one of the significant developments in the food engineering industry. Once these products have been texturized and rehydrated they can be used as meat extenders or total meat substitutes.
Food manufacturers are interested in these products, because their use as ingredients imparts favorable changes in the structure, texture, and composition of the finished foods, at an attractive price. Those products which have been texturally and histologically restructured through processing have fibrous structures and integrity similar to that of muscle ti ssue. They can be produced by one of the two basic processes, wet spinning and thermoplastic extrusion [1]. The topic of this work is the extruded material.
Theoretically, the temperature of extrusion varies from
80 0 to 17SoC (180o-350 oF). There is very little degradation of the protein, which contains 20 to 40% moisture. The resulting pressure ranges from 14 to 60 atm (200-900 psi).
Al though the process has rel ied heavily on the theory of plastic extrusion, food extrusion cooking has some characteristics of its own. All aspects of production, 2 storage, handling and environment should be considered a long with economic considerations. At Ohio University, a melt transformation extrusion (MTE) process to produce highly oriented semi-crystalline polymers has been investigated by Collier [3J. In this process a plasticating extruder supplies molten polymer to specifically designed dies through a melt conditioner (medium pressure pipe). The molecules of the molten polymer are partially oriented by passing the material through this conditioner zone (2000-8000 psi) immediately before ex trusion through a converging die. As shown in this research, MTE was at a lower pressure range (500-2000 psi). This process was useful in enhancing the fibrous texture of soy protein. Reports have dealt with the extrusion texturization of soy protei n. The product characteri sti cs are thought to be dependent upon the following independent variables: screw speed, feed rate, moisture, product temperature, residence time, and protein content [3-5]. The objective of this investigation was to apply the MTE process to soy protein and to observe a definite layered structure of fibers in the soy protein extrudate under the predetermined conditions. Texture was used as the basic tool of observation. It can be viewed as a direct consequence of microstructure, which originates from chemical composition and physical
forces acting upon it. Scanning electron micrographs of the 3 inner layers will be used to reveal the morphology of the soy protein extrudate. Advantages of using the scanning electron micrographs in studying the ultrastructure of soybean and soy protein have been shown by previous researchers [6-8]. Optical microscopic observations have also been used in support of the textural observations. Chapter 2 BACKGROUND OF STUDY
In recent years texturized vegetable protein process for the transformation of powdered soy protein into a meat-l ike texture has received some acceptance and popularity. The simulation of meat depends on such textural characteristics as thickness, smoothness, cohesiveness, shear and friction forces [9]. It has been thought that this kind of texture develops with the formation of fibers. Fiber formation can be obtained through several process which can be either chemical or physical. Many new processes have been developed to yield textured protein products. The two most basic industrial processes for generating texture from proteins are spinning and extrusion. Spinning of protein fibers involves modification of the isolated protein through solubilization in alkali [10]. During the alkali treatment the globular protein unwinds and deaggregates to form a series of dispersed flexible chains. When the material is ready for spinning, it is forced into alignment through a porous membrane. Protein fibers (about 0.003 in diameter), which are partially oriented, are coagulated in an acid bath. The fibers are then stretched to a desirable strength and cut into a desirable size. The stretching causes further 5 orientation of the protein fibers.
On the other hand,' the thermoplastic extrusion process
is a simpler process. Researchers have detailed variations
of the basic thermoplastic extrusion process [11-14]. The
process involves plasticizing flour and water in an extruder
to high temperatures and pressure. The emerging extrudate
flashes off steam and expands, resulting in a dry and
textured product. This technique has been chosen for this
study because of its advantages over the spinning process
(table 1), and its similarities to the MTE process. Other
processes that are less popular are gelation [15J and direct
steam texturization [16]. Thus, extrusion is not the only
method of texturization [17]. Further details on the
extrusion process and soy protein will follow in chapter 3.
Table 1. Extruded versus Spun Texturizing Ingredients [14J
Advantages Disadvantages Thermoplastic *Inexpensive *Limited use extrusion *Simple process *Poor structured *Good protein quality analogue texture *Can absorb water *Flavor, color and fat *Thermodynamically effecti ve Fi ber *Versatile *Expensive spinning *Good structured *Technically difficult analogue texture *Low protein quality *Flavor, color 6 2.1 Protein
Native protein molecules are known to be folded with well-defined, unique three dimensional structures. Princi- pally the molecules of proteins are made up of carbon, hy- drogen, oxygen, nitrogen, sulfur and some traces of phospo- ruse The protein consists of small units, called amino acids. These amino acids play a very important role in pol ymer t za t t on to form a long chained molecule. They have toe following chemical formulas typified by [18]:
leucine lysine
CH CH 3 3 >CH~HCOOH >CHyHCOOH CH NH CH NH 3 2 3 2 isoleucine valine
The amino (-NH 2) and carboxyl (-COOH) groups are chemically active, basic and acidic, respectively. Thus the 7 amino group of one amino acid readily combines with the carboxyl group of another and forms a peptide bond at the center (eq. 1).
o R II I '-CH NH 2-R 2-COOH + NH 2-R-CH 2-COOH -- H2-y-C-j-I-COOH + H20 R' HH (1) dipeptide
The remaining free amino and carboxyl groups at the end can react with independent amino acids to form polypeptides. The possibility of variations among proteins is enormous. This variation depends on a combination of different amino acids, different sequences of amino acid wi thi n a cha in and di fferent shapes the cha in assumes. The chain can be coiled, folded or straight. These differences are responsible for the differences in texture of the proteins. This complex configuration of a protein can be modified to form fibrous texture by subjecting the material to external forces utilizing protein psychochemical properties (dough forming, film forming, moisture holding, emulsifying, thickening, gelling, stabilizing, cohesiveness and others [19]). 8 2.2 Soy Protein and Its Co.mercial Use
The utilization of soy protein depends on its functional and physical properties, nutritional and economical values. The functional value of soy protein, including its physical and chemical properties, have been reported [20-22]. Some of these properties, such as emulsification, viscocity and water holding capacity are important in meat formulation. These functional properties, which contribute performance aspects in affecting structure and texture formation, outweigh their nutritive contribution [23]. There are three types of commercially available soy protei n: soy flour (1 ess than 65~ protei n ) , soy protei n concentrate (65 to 89% protein), and soy protein isolate (90% and higher protein) [23-24]. All three types of these products can be used to yield a range of textured vegetable protein; the cost increases with the protein concentration. A typical analysis of soy protein concentration is tabulated in table 2. Soy concentrates (70%) is used as the raw material in this study. There are three dietary uses of texturized vegetable protein (TVP) [26]: 9
Table 2. Typical Composition of Soy Flours, Concentrates and Isolates [25J Per cent (moisture-free basis) Soy flours Concentrates Isolates Protein 56.0 72.0 96.0 Fat 1.0 1.0 0.1 Fibre 3.5 4.5 0.1 Ash 6.0 5.0 3.5 Carbohydrates (soluble) 14.0 2.5 0 carbohydrates (insoluble) 19.5 15.0 0.3
Table 3. Amino Acid Compo st t ion'' [26J
Amino Acid Soy flour FAO breference protein
Arginine 7.0 2.0 Histidine 2.4 2.4 Isoleucine 4.2 4.2 Leucine 7.7 4.8 Lysine 6.4 4.2 Methionine 1.0 2.2 Methionine + cystine 2.2 4.2 Phenylalanine 4.7 2.8 Threonine 3.6 2.6 Tryptophan 1.7 1.4 Valine 4.4 4.2
aI n, grams per 16 g N. bFood and Agticulture Organization 10 (1) Analogues: products which are made to resemble another product. (2) Supplements: products which are made to meet a deficiency. They are not added for textural purposes but for their functional properties, especially to bind fat and moisture.
(3) Extenders: to stretch out food which is available. This is the most common use for extruded textured proteins. They can be used with meat to reduce prices and, in some cases, to improve quality.
It can be seen that in nutritional value the TVP is comparable to meat. Soy protein is known to contain all of the essential amino acids needed by the human body, except it has a lower than desirable content of sulfur-containing methionine (table 3). Hegarty and Ahn [27J proved the nutritive value in soybeans by comparing soy-based meat analog with ground beef. Finally, soybean protein is abundant, commercially available and inexpensive. It is the largest cash crop in the United States, exceeding corn, wheat and cotton. It is used extensively in the food industry. The price of the texturized materials range from 27-45 cents per pound on a dry basis, which after hydration translates into a 9-15 cents per pound meat replacement [25]. 11
2.3 Mechanis. of Fiber For.ation
The mechanism of protein texturization during extrusion cooking is not clearly understood. Many researchers have reported that the extruder environment enhances the trans formation of amorphous soy protein to fibrous microstruc tures [14,31,59-63]. A fiber is defined as a body of matter having a high ratio of length to lateral dimension and which is principally composed of longitudinally oriented linear molecules [28]. Fiber can be thought of as a result of realignment of protein subunits that are disassambled due to pressure and heat of the extruder environment. This re alignment is done by the shearing action of the extruder [29,30]. Smith emphasizes that the cooking extruder has the ability to work dough to restructure and retexture the proteins [31].
Thermal denaturation, which is the key parameter of texturization, involves gelation and restructuring. The process is irreversible and is described through a sequence of steps. Figure 1 shows the formation of hydrogen bonds and amide bonds between aligned molecules in a denatured state. During heating, the ionic, disulfide, hydrogen bonds and van der Waals' forces organizing and holding the native globular proteins are interrupted and the hydrated proteins begin to unfold. The relatively linear protein chains are 12
Native state
unfolding
Associating Amide bond
Figure 1. Mechanism of Protein Denaturation [23J 13 oriented through a shear environment, so that the reactive sites on adjacent molecules can cross-link the protein to achieve a fibrous texture [29,30,33]. Previous reports suggest that formation of fibers involves the formation of certain types of intermolecular peptide bonds (see section 2.1). The work of Cumming et al.
[34] describes the pressure and temperature influences on the dissociation of soy protein into subunits which subsequently become insolubilized and form high molecular weight aggregate. On studying the formation of spun soy fibers, Jenkins [35] demonstrated that the fibrous texture of extruded soy protein can be improved by adding an elemental sulfur-containing adjunct. It is believed that molecular changes occur in the elongated curled protein molecules by lateral reaction of the cystine bonds
{NH - CH- C0 formed by amino acid groups between the 2 2H)2 peptide chains, which are generally parallel and overlapping. In 1976, Burgess and Stanley [36] suggested that lIisopeptide ll crosslinking may playa role. They assumed that crosslinking of protein chains occur through amide bonds between free carboxyl and amino acid side groups of the protein chains. The energy for the endothermic denaturation process consisting of breaking and forming of new bonds was determined using differential scanning calorimetry to be endothermic (90-100 KJ/KG) [37]. Sensible heat changes 14 occuring because of temperature rise in the product must also be considered [37]. Qualitative changes in soy protein during high temperature heating are shown in table 4. Table 4. Changes in Characteristics of Soybean Protein at High Temperature Heating [29J
Temperature of heating (OC) 100 105 110 120 130 140 150 160 170
cross-strlicture of subuni ts intact 1i ttl e degraded ..1* degraded---- solubility rapid decr-ease-s--s l ow increase ..I- rapid increase-- binding force (degree of aggregate) rapi d i ncr-ease-s--e low decrease .1- rapi d decrease-- expans i on property increase .... rap; d decrease------texture hard fragile ..,.. soft elastic •to. like sol------
...... 01 Chapter 3 THEORY
When a bulk polymer is crystallized in the absence of external forces, there is no preferred orientation of crystallites or molecules. Orientation, which is defined as the degree of alignment of polymer chains in a particular direction, is greatly influenced by deformation and ternperature gradients in the system. As the polymer becomes oriented, the mechanical and physical properties improve
[28,38].
3.1 Melt Transfor.ation Extrusion Process (MTE)
The MTE is a thermoforming process. The objective is to deform a polymer melt, and to align the chains in a common direction or directions. This process has advantages over other orientation processes, since orientation is induced in the molten state. In the molten state the deformation can be quite influential; organization at all dimensional levels can be affected either directly or indirectly: the basic molecules, the aggregate-crystallite, the crystalline amorphous entity, the single crystal lamella, and the larger 1 7 aggregation, called spherulite [39]. The orientation due to the deformation may be developed in glassy or amorphous polymers, as well as in crystalline polymers. Since the amorphous chains have not experienced crystallization, they do not gain appreciable strength by orientation because they fail by separation rather than by chain scission. In the crystalline polymers, the crystallization is enhanced by chain alignment.
3.1.1 Shear Stress and Flow Induced Crystallization
In the molten unoriented state, the linear molecules are randomly coiled. Upon supercooling, the polymer tends to crystallize and form spherulitic structures with no macroscopic orientation (figure 2). The stacking of parallel lamellae of the substructures produces a high local order among the amorphous or disordered regions. Flow induced crystallization and a shear field can produce a high deformation. Mechanically, this causes the forming lamellae to begin to slip from their originally preferred alignment, such that the polymer axis becomes a l i qned in the orienting direction. The extension due to flow of the folded chains forms stacks of parallel lamellae that can be either along or against the lamellae axis [40]. Figure 3 shows this behavior in a crystalline polymer. Sphtrut,'ic choins folded at 18 riQht anQ~ to main alis Amorphous Inter - spherulj,ic material
Defect, in fibritt
Amorphous intff- fibril tor material
Single .> crystal nucleus Spheruli'e
Figure 2. Structure of Spherulite [28J
~~---_. ( a )
( b )
Figure 3. Suggested Model for Fiber Formation (a) By unfolding of molecules from more than one lamella, (b) By gradual chain-tilting, slip, breaking off blocks of folded chains 19 Upon approaching the entrance region of the die, the velocity distribution of a molten polymeric material changes to a "wine glass stem shape" (figure 4). The flow streamlines converge rapidly inducing an elongational effect of the previously random coiled polymer chain and giving a higher degree of orientation [41-42]. The rate of uncoiling of the polymer chains at the converging section depends on the deformation ratio and the type of polymer processed [43,44,48].
Previous work using plastics on the MTE process describes the four important processing conditions which contribute to the amount of orientation in the extrudate [43,44,46-52]: (1) die design and deformation ratio
(2) screw or line speed
(3) operating pressure (4) temperature profile
The MTE process has been used with dies having reduction ratios from 2:1 to 16:1, with half angles ranging from 10° to 26°, and die geometries that deform the melt in either uniaxial or biaxial directions. Furthermore, fiber, ribbon and more complex dies have been used along with this process
[44,46-52]. Extrusion rates, controlled partially by screw speed, govern the level of deformation on the polymer melt, as well as the orientation. 20
!, : 1 n (= 0 n f 0 rm d t ion
z
Flow streamlines
Crystal growth tront and i sot herma 1 line
Figure 4. Elongational Flow in the "Wine Glass Stem" Region of a Converging Die 21 3.1.2 Pressure Effect on Crystallization
As proposed by Brown [53], the development of the extended chain crystals may be related to the formation of the nematic Illiquid crystals." A nematic structure consists of a parallel stacking of rods with relatively perfect internal structure, but not necessarily matched from end to end (figure 5). Collier postulated that a liquid crystalline form could occur in the materials studied under critical temperature, pressure, and field conditions [2]. This behavior of different crystalline structures (polymorphism) is not limited to the simpler polymers but is also observed in proteins and synthetic polypeptides [54,55]. In the case of synthetic polymers, the working pressure for MTE ranges from 2000 to 8000 psi, which is 1/4-1/5 that of a solid state extrusion [56].
Thermal properties Earlier observations of oriented (extended) polymer have shown a higher melting point than that of a random melt (quiescent) [43.44,46-52]. In terms of entropy change, ( 2 )
The melting points are,
( 3 ) 22
y )-'2 X
(
(D
Figure 5. Nematic Liquid Crystalline Form 23
( 4 )
where subscript f stands for fusion, q for quiescent, and ex for extended. As,
( 5 ) then,
T T 6.5 ~Sf ( 6 ) m / m = f / ex q q ex from ( 2 ) ,
T / T 1 or T T ( 7 ) m > m m ex mq ex > q
Tm = Tm -Tm ( 8 ) ex q
Hence, the melting point of polymeric material is directly related to its degree of orientation. 3.2 Extrusion Cooking
Extrusion, in general, refers to the shaping of the products to the desired size and consistency by forcing the material through a die under a high pressure. Extrusion has long been used in the food industry in the making of special shapes of food products (e.g. macaroni, bacon bits). Previous researchers have shown that the extrusion process ca n produce mea t 1i ke fi ber s [14,31,57-61]. These repor ts provide the "s t a t e of the a r t " of protein texturization by using the extruder. The basic patents of soy protein extrusion are those of
Atkinson [62] and Jenkins [35]. The newer patents, which were an improvement over the prior patent, did not use a die on the extruder and therefore had a lower pressure drop (below 200 - 500 psi); the resultant product's characteris tics were less spongy, less hydrated, and more fibrous [57-59]. Food extrusion owes much of its design and theory to plastic science [37,42]. However, it should be noted that there are differences between plastics as 'chemical', artificial polymers and protein as "b t opol yme r s !, natural polymers. Zuilichem [63] explained these differences as:
1. Biopolymers shows no spontaneous melting-temperature or trajectory but simply need a certain amount of shear to 25 plasticize the protein-water mix. 2. The biopolymer is highly sensitive for a long time span of exposure to heat and pressure.
3. It is important that some water be present during extrusion to assure a continuous working condition of an extruder.
The main components of a food extruder are the same as those of a thermoplastic extruder. They are: feeder, compression screw, barrel, d t e Ls ), and heating system. In this process, moistened products are plasticized in a tube by a combination of heat, pressure, and mechanical shear. Figure 8 shows the basic process in the food extruder barrel, which i s divided into 3 stages: mixing and compressing, heating and cooking.
DRIVE, GEAR FEED RE DUCER HOPPER a COOLING THRUST BEARING WATER \ JACKET PRESSURE TRANSDUCER
THERMOCOUPLES / DIE
DISCHARGE THERMOCOUPLE
BREAKER PLATE BARREL WITH FEED COMPRESSION METERING HARDENED LINER SECTION SECTION SECTION
SCREW WITH INCREASING ROOT DIAMETER
Figure 6. Cross Section of a typical food extruder [39] 26 (1) Mixing and Co.pressing (feed zone) The moi stened material enters the extruder through the feed zone. The relatively free-flowing granular particles of the meal cause a turbulent like pattern in the intake section of the extruder. This flow insures intimate contact of protein with water with very little internal shear of food. Then the screw further compresses and mixes the product. No cooking is desired in this zone [64].
(2) Heating (transition zone) The second zone continues the mixing action, and concomitantly imparts heat into the mixture due to shearing action of the screw. This heat is used by the proteinaceous material to coagulate and polymerize. This transition from solid to a fluid is associated with a set of chemical reaction called 'cooking'.
(3) Cooking (.etering section) The meaning of cooking here is the conversion and/or reaction of the major food constituents - carbohydrate, fat protein, and water. Two types of cooking reactions which occur with food biopolymers are protein denaturation (section 2.2) and starch gelatinization. In these reactions, water and food materials themselves interact to create new, altered forms which have a distinctly different rheological behavior. This cooking process is time and temperature 27 dependent, which probably changes with the concentration and quantities of the chemical species present and the shear environment. Food extrusion results in the chemical alteration of the feed ingredients through the cooking and texturizing process and in this respect is significantly different from the melting processes, which occur during the extrusion of thermoplastic resin. Thus, the application of the words 'melt' or 'melting' is a misuse [39J.
Most of the cooking is done in this critical zone. The cooking is mainly done by externally supplied and viscous shear heat as the material is conveyed through the barrel to the die. The highly turbulent flow pattern is transformed into a laminar flow to minimize back flow across the protein strands. At this stage the materials are simultaneously oriented and coagulated in the direction of the chamber.
During this whole process, the viscocity and physical properties of the dough can differ drastically. Information about this is very limited. According to Briskey [65] and
Hermansson [66], the viscosity of the system changes with the degree of protein hydration.
Therefore, the variables of extrusion processing conditions are,
1. temperature profile 2. screw speed/line speed
3. design of die(s) 28
4. moisture
5. pressure profile, and
6. residence time
3.3 Characteristics of textured protein products
A variety of tests have been used to characterize the texture and other properties of textured protein products.
These tests are used to determine the effects of varying extrusion conditions on product characteristics, and to maintain quality standards for production runs. Comparison of results from different investigations is difficult, because no standard set of tests is used [37J.
Only two types of tests were possible in our laboratory: bulk density and water absorption (hydration value). Bulk density gives the degree of expansion of the extruded dried products, while water absorption gives the degree of po r o s i ty of the products' textures. Water absorption is an important functional property of textured protein products as the products are used after rehydration.
This value gives an indication of the extrudate maximum absorption and retention capabilities. Hydration conditions vary in different laboratories. 29 3.4 Response Surface Analysis (RSA)
It is convenient to visualize geometrically the relation between response and the various factor levels. RSA method represents the response by assuming that when k factors ( or independent variables, exist in an experiment, the response (or dependent variables) will be a function of the levels at which these factors are combined
[61].
( 10 )
The function ~ is called the response function.
The response surface is represented by a polynomial. For the case of three variables, a quadratic polynomial was proven adequate to fit the data [3-5]. The model is,
( 11 )
The above equation takes into account variations due to first and second degree as well as those due to i nt e'r action s • Response of the independent variables in a certain region is represented by contours. These surface contours are obtained by making one variable equal to a constant 30 value and then solving the fitted equation as a quadratic equation in the other two.
The application of this method in food industry is quite popular [3,45,68]. Chapter 4 DESCRIPTION OF EQUIPMENT AND MATERIAL
A. Extruder A laboratory single-screw extruder, C.W.
Brabender, Model 200, had the following
11 specifications: barrel diameter - 0.75 ; LID 20:1;
feed hopper gravity feed; heating 2 zone
electric heaters, independently controlled by 800 watt heaters monitored by two West Model JPC on-off proportional controllers; drive unit
variable speed motor assembly, equipped with a tachometer, and capable of controlling screw speed
from 0-200 RPM. The discharge pressure was
indicated on a West Model 1586 pressure indicator
with a range of a to 10,000 psi. The motor speed
was controlled by a Fincor 2400 MKII DC Motor Controller, manufactured by INCOM, International
Inc.
B. Extruder Screw The screw used was made of 4140 chrome alloy with a standard compression ratio of 2:1. It had 20 flights with increasing screw root diameter from 0.475" to 0.605 11 with a 0.608" axial channel width 32 and a 0.007 11 flight clearance. Angle of the helical screw was 25°.
c. A Melt Conditioning Pipe A 15 11 length pipe (medium pressure-lO,OOO psi) with 111 outside diameter and 0.687" inside diameter was used as a connection between the barrel and the die •
D. Extruder Dies
..; The dies were made of 304 stainless steel: (a) A split die with a uniaxial deformation ratio of 6:1 was used. The die opening consisted of a slit 1/16 11 thick and 1/2 11 wide which produced a tape or ribbon like extrudate. (b) A fiber die with a circular opening of 0.020"
diameter and 111 length was also used. This die was fitted to a holder and produced a string-like extrudate. Each of the above dies produced a vertical, downward extrusion and were heated with fitted 600 watt heaters controlled automatically from the control board. Figures 7 - 10 show the designs, dimensions, and views of the dies. 33 o • -1/16" 1/2" J
L--- -2 1/4"----- 3/16" ------3 1/2..------......
Figure 7 . Schematic Diagram for the Uniaxial-ribbon Die (A) Side view, and (B) Top view 34 4.
...... t:-:-:-:·:-:-:-:· ...... t:::::::::::::::: \9 ~: . I -CD ~,
4 /~ --. II8 1
~ f ",... -It) = "- • ...'". 10 ::::::::::::::::~ J" QJ ..c: -4->
S- o 4-
E rtj S- O) -+-- rtj It 9 /1.--+ 0
U QJ .,.... .,.... -4->0 ~ rtj E S- ~::::::::::::::: QJ Q) ~::::::::::::~ ..c: ..0 r u·,.... -r = =f U1 u, N ,...... • "' " "PI) r- ~:::::::::::::::i ,.... co r'i"••••••, •••••••• :::::::::::::::::Il I QJ S- 1 ~ L 0) .~ .. .. lJ.. 35
Figure 9. Photograph of Uniaxial Die Halves
Figure 10. Photograph of Fiber Die Pieces 36 E. Controllers Two of the three Gardsman temperature control units manufactured by West Instrument Corporation were used to control temperatures in the barrel.
They had a range of Q-800oF (425°C). The tem peratures in the piping and the dies were controlled with two Love Model 52 controllers mounted on the control board. They had a range up to 400 oC. Temperatures and pressures in the barrel and the die were sensed by Dynisco strain gauges,
r~1 0 del TPT 43 2 A-I QM- 6 / 18 , and measure d byaWest
Model 15-86 and a Dynisco Model ER 478Al pressure gauges.
F. Optical Microscope A Wild M5A Stereomicroscope was used for
texture observations i n the 1abora tory. The overall magnification range was 1.4X to 20QX, depending on the optical combination.
Photomicrographs of the structure were taken by MPS15/11 Semiphotomat (632.8 mm) assembled on the M5A Stereomicroscope using a 35 mm film (ASA
400/DIN 27).
G. Scanning Electron Microscope (SEM) A Hitachi Model HHS-2R Scanning Electron 37 Microscope was used to photograph the sample on positive/negative black and white Polaroid film,
type 665 (ASA 75/DIN 20). The SEM is capable of viewing three-dimensional structures over a range
of 20-280,000 magnification.
H. Sputter Coater Prior to SEM examination, the samples were coated with gold or gold/palladium deposition in a
Hummer V sputter coater, manufactured by Technics.
I. Differential Scanning Calorimeter A Perkin-Elmer, Model DSC-1B differential scanning calorimeter was used to detect the melting point of soy protein. This equipment was connected to a Perkin-Elmer, Model 56 chart recorder to plot the rate of heat input versus temperature.
J. Soybean Defatted Soybean protein concentrate, PROCON 2000, was obtained from A.E. Staley, Mfg. Co.,
Decatur, 11. It contained 70% protein on a dry solid basis and 5-7% moisture. Tacla••• t.r
r------Pr••• ur. - T.. p.raturt , Gauae ~ o
Zonf 1 Zone 2 Zone 3 Zonl 4
~ I 8 a r r • I leo nd I t Ion. r Z 0 n e 1-Die
Figure 11. Schematic Diagram for the Extrusion Process with a Conditioner Zone
w cc 39
c: .,...o
OJ ..s:: +-> 4- o
.,... :>
Q) S ::s 0')
u, Chapter 5 EXPERIMENTAL PROCEDURE
All the samples tested in this investigation were prepared by extruding premoist soybean flour in a C.W. Brabender laboratory extruder, Model 200. To complete the screw assembly, a conditioner zone (18" spacer) was placed between the die plate and the barrel, which provided additional volume after extruder screw discharge. Previous workers proved that the conditioning zone improved pressure uniformity behind the die plate, increased the residence time of the material in the extruder, and improved crystallization [51,52]. All compression fittings in the assembly line were torqued to 75 ft-lb (figures 11 and 12). Prior to setting up, the die channels were cleaned from old polymer by sanding with 600 grit sandpaper. The ribbon die halves were assembled with six 0.25" X 2.5 11 grade eight socket head cap screws, which then were torqued to 90 ft-lb. All t he r mo coupl e s , transducers were tightened to prevent any leaking during operation. Independent variables selected for the process were temperature, feed moisture and screw speed. The selection of these critical variables were based on findings reported by previous researchers and through preliminary experimentation 41 [14,31,59-63]. The dependent variables are pressure profile and line speed.
6.1 Preliminary experi.entation
The first objective was to find the best temperature profile and processing conditions. The extrusion assembly was divided into 5 temperature zones: I and II - the barrel, III and IV - the conditioner zone, and V- the die (figure
11). Through preliminary experimentation, it was necessary to force feed the material through the hopper. The premoist soybean was ground by the screw and pushed back into the feed hopper. Because of the considerable amount of steam generated, the soybean developed a tacky consistency and clogged the feed inlet. This effect was reduced by not heating the section nearest to the hopper. If this section were heated, the steam would be absorbed by the incoming soy material. The steam caused caking and made smooth operation impossible. The temperature settings for the assembly were determined by careful observation of extrudate quality. A decreasing temperature distribution toward the die was a better choice than that of an increasing temperature distribution. The former case had two advantages: 42 (a) Most of the cooking was done in the barrel zone. A decreasing temperature distribution prevented de gradation of the material. (b) The material did not extrude at too high a temperature in the die. Excessive expansion caused by flashing steam could destroy or seriously limit the formation of the fibrous structure, however, a certain amount of expansion of the product was also important in order to obtain a fibrous structure.
In the past, a steep temperature gradi ent was appl ied to enhance and freeze the highly oriented extrudate
[48,51,52]. This was usually done by immersing the tip of the die in a water bath as a cooling medium, which also caused the pressure to build up. In this study, the effects of the die land temperature gradient were not observed to occur.
The die temperature was heated to SOOC, since a lower temperature caused the material to stop flowing out of the die passage. Too high a temperature (100°C) at the die made the product emit separated bursts of burnt individual pieces. It appeared that some pieces would stick in the die nozzle until the pressure built up sufficiently to dislodge them. The material near the end of the die expanded rapidly, producing a rapid outflowing of material which fragmented into individual pieces. This product was unassayable. 43 Once particular processing temperatures were set, a series of experiments with the same temperature setting were conducted. This reduced excessive use of raw material during the transition periods to a new temperature settings. Since the extruder was not self emptying, too little moisture, too high a temperature, and too high a compression ratio were all avoided because any of these would cause the materials remaining in the barrel to harden and lock the screw [69]. A blocked extruder, due to overheating or high frictional drag of the product, costs a considerable amount of maintenance time for dismantling, cleaning and repair. An experimental design was chosen with three levels of temperature, three levels of moisture and four levels of screw speed to allow estimation of second order effects in the empirical statistical model for three independent variables (table 5). Table 5. Experimental Pattern of Processing Condition Codes
Processing temperature profile, Zones II - III - IV (OC) 140 - 115 90 150 - 125 - 100 160 - 135 - 110
M0 i stu r e RPM RP ~1 RPM wlo 40 60 80 100 40 60 80 100 40 60 80 100
30 Al A2 A3 A4 01 02 03 04 G1 G2 G3 G4
35 B1 82 83 84 E1 E2 E3 E4 HI H2 H3H4
40 C1 C2 C3 C4 F1 F2 F3 F4 II 12 13 14
Note: The temperature at zones I and V were unheated and 50°C, respectively
~ +::at 45 6.2 Experi.entation
DRY a WET SOLID - LIQUID ...... INGREDIENTS BLENDER
... .- AFTERDRYER . .... EXTRUDER. ,
Figure 13. Simplified extrusion flow sheet
Figure 13 shows a simplified flowsheet. Moisture was added to the soybean meal prior to extrusion because the residual moisture content of the meal after oil extraction is normally very low (5-7 weight percent or w/o) [69]. As the present design did not allow direct water addition in the extruder, a food processor was used for moistening the powder. In order to have a uniform product, a food processor was used to mix the dry flour with water. Distilled water was added slowly along with the continuous mixing and breaking action of the steel blade, so that it maintained a free fl owi ng movement of powder to prevent the development of large aggregates. Water addition was accomplished in 3-5 46 minutes and mixing ceased after an additional 3 minutes. Batch sizes were normally about 300 grams of dry blend. Once the temperature settings on the extrusion system were reached, the motor was turned on and the screw speed was adjusted to achieve the desired tachometer setting. Then the hopper was fed with premo;stened soybean meal. In order to achieve a continuous feeding, the mix was hand-fed to the extruder hopper. An excessive amount of mix in the hopper prevented free flow of the material into the extruder because of caking or bridging of ingredients in the feed hopper. Sufficient time (20-30 minutes) was allowed in order to have a steady state system. Estimation of the steady state was based on the temperature and pressure readings. After enough material at each shear rate had been produced (.!.15 feet), the screw speed was changed to another desired shear rate. Elapsed time was allowed for the transition period (20 minutes). Data collected consisted of the steady state values of temperatures in all zones in degree Celsius, pressure at the exit of the barrel, pressure at the die in psi, and extrusion rate in in/min. Table 5 shows the variations of variables selected. Extruded samples were collected, placed in sealed plastic bags, labeled with the extruder run codes and refrigerated. 47 The second objective was to analyze the effect of using higher pressure conditioning. Higher pressure drop at the die was attempted. This was done by replacing the ribbon die with a fiber die. Temperature profile chosen was unheated 160-135-10Q-50oC and screw speed of 40, 60, 80 and 100 rpm.
c. Speci.en Testings
All the samples were photographed and tested for moisture absorption capacity, bulk density and thickness. It was necessary to examine the specimens as soon as possible because the extrudates will not remain fresh due to microbial and enzyme action. Under refrigerated conditions the material lasted only for 2-3 weeks. Water absorption capacity was evaluated by soaking 50 grams of extrudate segments in a beaker filled with 200 ml water. After 15 minutes of rehydration, the excess water was removed by draining with a tea strainer for 15 seconds. Afterwards, the sample was reweighed. The percent water absorption was calculated as the percentage weight increased based on the dry weight.
Bulk density was determined by weighing 12-in long extrudate. The volume was obtained by multiplying the length by average width and thickness. Average degree of puffing was 40.8S; puffing is defined as the degree of extrudate's 48 volume expansion due to pressure drop and flashing of the water vapor. The product density was obtained by dividing the weight by the calculated volume. Microscopic Examinations were divided into two stages, optical microscopic and Scanning Electron f4 i cr 0 9 rap h s (S EM). Sam p1e s for 0 ptica 1 microscopic studies were taken immediately after they were extruded, because they were still moist and easy to layer.
Preparing samples for SEM was more complicated than for the optical microscope. However, only a small area of the sample can be viewed at one time. The samples obtained during the extrusion were frozen in liquid nitrogen. Samples for SEM were placed onto a specimen stub covered with double-coated cellulose adhesive tape. The area around the specimen was coated with a small streak of silver conductive paint in order to minimize charge build-up from the primary electron beam. Afterwards, the specimens were coated with gold-palladium (60:40) in a sputter coater. The coated specimens were examined in a Hitachi scanning electron microscope, Model HHS-2R. The photographs were taken on positive/negative black and white Polaroid film (ASA 75/DIN
20) • Differential Scanning Calorimeter (OSe). Samples were cut into thin pieces and weighed to the nearest tenth of a milligram. They weighed approximately 5-15 milligrams. Then they were sealed into specially designed aluminum pans 49 supplied by Perkin-Elmer and placed on the Perkin-Elmer DSC unit. The instrument was calibrated with a standard heavy Indium sample (163.S oC melting point) at 20°C/min and a full scale deflection of eight millicalories. The recorder was set at a full scale range of five millivolts and the chart speed was set at 40 rom/min. Statistical Design. The data were analyzed by means of a stepwise multiple regression. The analyses were performed using the extrudate characteristics as dependent variable versus the processing temperature, screw speed, and moisture. All possible subsets of the regression were performed using the SAS package [70]. Then, response surface plots were made from the derived regression equations. Chapter 6
RESULTS
A series of experiments was conducted according to the above design. The intent was to investigate the effect of independent process variables upon dependent variables. The protein concentrates used on all runs were assumed to contain 5% moisture prior to any water addition. The results of response surface analysis are tabulated in tables 11 and 12 in Appendix C. The response surface plots include all the experimental design data and the predicted data. These plots illustrate the contour of the dependent variable against two of the independent variables, while setting one of the variables constant. Response analysis usually predicts the area with optimum response, e.g. highest output, highest absorption rates, etc. The shape of the optimum, the "center of the s y s t e ra'", can be a maximum, minimum, or a mix of the two, a "saddle point". The results of the dependent variables of this study show a
"saddle po i nt " which implies the existence of two distinct regions of maximum yield a two peak system (figures 23, 29, and 32). The area of the two peak system means that there are two maximum peaks in the system. Sometimes the center of this area is found outside the experimental design. The surface in this region of the experiments represents either 51 an inclined ridge or an inclined trough. The effects of screw speed on extrusion rate or volumetric flow rate was primarily a function of screw speed. Figures 14 and 15 show the trends at different moisture contents and process t emp e r a t ur e s , respectively. Moisture content effects were more significant than that of processing temperature. Higher moisture content produced caking of the material t reducing output rate. Process temperature effects were more dramatic at lower screw speed and leveled off at higher screw speed. Effects of all the three processing variables are represented by the response surface plots in figures 16 and 17. For examp l e , in figure 16, the effect of screw speed and moisture on the extrusion rate at a constant temperature is represented by five symbols. The darkest symbols, at the upper left of the figure with a value of 62.18 to 69.53 inches per mi nut e , represents the highest value range of extrusion rate shown in this figure. The value occured at a screw speed of 90 to 100 RPM at a moisture content of 20 to 22.5 weight percent.
Decreasing extrusion rates are represented by the other symbols along contour lines, at roughly 15 inches per minute interval. Figures 18 and 19 depict the pressure profile at the die versus screw speeds. This pressure was an indication of how much energy was required to force the material out of the die orifice. To overcome high frictional forces in the 52
RUNS. ZONE II. 0 ...!L '30%
H Vl A 35% ~ 41 --- c: OJ ~ I 40% c: 8 ...... o u OJ s; ....-..- ,..... ::::s c: .. ~ - :a: Vl " o ", :::: "' c c: -
..
. -0 Q) Q) D . 0 Vl 3: OJ s, z u o . V> -(/) Vl (J ::::s J Vl - s; a: a: Q) t ... > )( LLI Q) I&J :2 ~ ::) res ..J 0::: o c: 19 > o Vl :::::s s; ~ x w 15
OJ s; :::::s en o 20 40 80 80 L.L.. SCREW SPEED (Rpm) -----0 J .....----8 .,..",.""'- I 30 ------"", ",,--- .....A / a ...... / // . /' . 50 ,... ,... [] /' . a- &: A ••••• ~ ~/ /' ... ~ X -2 / . , ~ IQ '-- .. c: a: / . / ... -.....- ...., / . o /' . LaJ... /'"/ ...... 4( / ... 8: 11.I ... / ... ~~ C / .. o a: / RUNS ZONE II .J . &I. ,/ ~ ... z / ... c o o / .... o 140·C iii / . C J / .. I . F &&I .: .. o I eo· c Z l / / ..... J X /' . ..J &II / . C:i 160·C o / ..... > / ..... 10 5 ./ ..... r »: 0 1·····F; gure 15. Extrusi on Rate versus Screw Speed at 0; fferent Process; ng Temperatures . ...
I I 2.0 40 60 80 100 SCREW SPEED (Rpm) U1 W 54
Cn~!TOlJR PLOT OF SCREW SPE:::" (Pf"'~) "'.Jf' MrtsT'JPF: (~'/Q) CO~JTOURS AF c~t'JTrlJR PLC~ l'F X2*X3 t 1) + 1 J) I+ JIK~" ,.F8F8~@~e , R•• . PFpe?Q8A XXXXXXXXXXXX ~~+++++++++++ l .~ ~@pe6~eA~ XXXXXXXXXXXX. ++++~++~+ ...... ++ " FRcPT?€ee€ XXXXXXXXXXYX ++++++++++++++ I ~ ~~FGS~~B~ xxxxxxyxxx~xx +++++++++++++++ 90 + ~FP8~~8Q xxxxxxxxxxxxx ++++++++++++++++ ~~F@~P~P~ 'XYY~XXXYXXXX +++++++++++++++++ 5 ~FGFPQe~ XXXXXXXXXXXX +++++++~++++++++++ ~8e~eQFQ_XXXXXXXXXYXX +++++++++++++++++++ p ~PP~A.XXXXXXXXXXYX ++++++++++++++++++++ F') I rF~~~P + XXXXXXXXXXXX. ++++++++++++++++++++ 8e-ef:lE- \ '( XX X XXX XX XX ~ ++.. +++ ++ +++ ... J ~~FP~ X~XXXXXXXXXX ++++++++++++++++++++++ PA8~ .. XX~XXXXXXXX +++++++++++++++~+++++++ 1 ~F yxyx~x>:xxxx ++++ ... ++ .... ++++++ ...++ .....++++ ...~ 7J + H~ xxy~XXXXYX +++++++++++++++++++++++. 1 4;, X)(XXXXXXXX. ++ .....++ ... ~++++++++++ ...++++ ••• 8 .. XXXXXYXXXXX +++++++++++++++++++++ X X X ' y •••••• IO.72L58 18.074t:;2 ++++...... 18.07492 32.775:59 XXXYXX :12. 7755 ~ 47.47E?6 PFRQSe 47."-7626 (,2.17()q~ ...... 62. 1 7(,C)~ (.,Q .52 7 2 () Figure 16. The Effect of Screw Speed and Moisture on the Extrusion Rate at a Constant Processing Temperature of 150-125-100-50°C. 55 CONl"OUR PLOT OF TEMPERATURE (e) AND MOISTtfAE. CONTeNT (W/O) CONTOURS ARe E>eTRlIsrON RATES (IN/MIN) CONTOUR PLOT a~ Xl*~3 1 c. .)• ;..; +I _K.~ FPPF~~P XYXXXXXXXY ++++++++++++++++ ~~_ PFF~~g~ xx~~~xxxx ~+++++++++++++.+ •• , ~~ ~papeF-F-~ .xx.xXXXXYX>'~+"'''''"+",~+,,+++,,,+ •••• ~ FQFEE8E XXYXXXYXX ++++++++++++++ ••••• 15 7.5 + . FP~~8~ XXXXXXXXy +++++++++++++~••••••• RER~~8, ~,~X)(XXXXXX ++ .... ++ ... +++++++ •••••••• Q8ee~F~ xxx~yxxxx +++++++++++++ ••••••••• P~A~PR XXXX~YXXX. +++++++~+++~+ •••••••••• I 8~F:.::.P~· lSS.J +, y.xxXy)(XX)(X ++++++ + ++ . AQ~~O .xxxxxxxx~ ~+.+++++++++ •••••••••••• ,. ~~Q., ) MOl STU~E ...... ;' I, • J? ~ c: ~ .,~. tJ~R~.? x'Xxx~x ? r;. r'J2 Rf...·? 4-;. ?~4)(~ EEdFF€ 4'":9 •.~:_:4i)(J ~·~.7::t"'0 6c;.6QIQl Figure 17. The Effect of Processing Temperature and Moisture on Extrusion Rate at a Constant Screw Speed of 70 RPM. '1' ------£ 1300 f ....-- ~ -----!------~ ..., -- ...... <, ~--. I / " ..., " tI: ~ ::) ••••••• """'M' ?1 en ...... ·········t ~ '~-...... (I) ...... LLt .. g: ... ------A. .-.. ...... &LI Q - ••...•••..••...•.•··M.••..••••••• 700 J 20 40 60 8 0-- --~--~IO() SCREW SPEED (Rpm) RUNS ZONE II Fi gure 18 . Die Pressure versus Screw Speed at Different Processing Temperature s A 140·C 0 A -_0 ...... ISO·C (J"1 G 160·C 0"\ ~ ' ...... 57 ~ . : . ~ ...... , c cu S cu 4 4- "'0 cu cu c.. V1 ~ cu S U V') til ::::s til (/) S-~ cu c: >cu ~ cu c: S- 0 ::::su til , o (/) cu cu S • a...... ,S- ~ cu.,...(/) ',... 0 I C):E .,... u, o o o o o o It) If) M) - - (I lei) lynSS3Yd 310 58 die land of the fiber die, pressure was increased to one and a half times that of the ribbon die (figure 20). Pressure variance was graphically represented with a 90% confidence limit. Response surface plots for the die pressure are on figure 21-23. A differential scanning calorimeter was used to detect the melting point and heat of fusion. The DSC was standardized using an Indium sample. The peak melting point occured at 430 oK, which depressed the actual melting point oC) (163.S by 4% (figure 24). Figure 25 shows the typical DSC scanning for the extruded protein product. Mel ting point did not occur and the decreasing curve indicated that the tested material experienced an endothermic reaction. This behavior will be further discussed in the next chapter. Figures 26-28 represent the correlations of extrusion parameters with product absorptions, or water retention value. The increase in water uptake implies that more water penetrated the structure. This is an important value because commercial texturized vegetable protein products are rehydrated prior to use, and rehydration characteristics of the cooked food is also important for digestion. Furthermore, the extrusion processing conditions influenced the protein to restructure and reduce its solubility. Bulk density of the dried extruded soy protein product indicated the degree of product expansion. This exothermic 1600' ( 1500 ...... • .....,Q. I.IJ ~ J CD en w ~ A. w o- 1000 20 40 60 80 100 SCREW SPEED ( Rpm) Figure 20. Die Pressure versus Screw Speed for the Fiber Die Runs (J1 1...0 60 ceNTOUR PLOT CF SCPEW jf'P:£:O (Pr'M) 'IS. 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The Effect of Screw Speed and Moisture on the Die Pressure at a.Constant Processing Temperature of 152.8°C (Zone II ~ 61 CONTOUP PLOT CF Tp:,JPf':"pATUnE r r j VS. r··OT~TlJPr CCNTE~~T ('1J/O) cnNTPUn~ ARF OYE PRESSUR~S (PSI~) crr~'TOU~ PLOT or xt*X3 I 160.0 + )(~XXXXXX +++++~++~ •••••••••••••••• xxxxxxxx +++++++++ •••••••••••••••• xxxxxxxx +++++++.~ •••••••••••••••• I eeEEA XXXXY)(XX ++++~+++~ •••••••••••••••• 157.5 + FP.F~RC XXXXXXX +++++~+++ •••••••••••••••• AFeP~ )(XXXXXX ++++.+++~ •••••••••••••••• ~F~8F XXXXXXX +++++++.+ •••••••••••••••• J 8E8~f? XXXXXX +++++++++ •••••••••••••••• 1'55.0 + 138R.. XXXXXXX +++++++++ •••••••••••••••• ee-8AP )(XXYXXX +++++++++ •••••••••••••••• T eefJ4=F XXXYX)(X +++++++++ •••••••••••••••• c= J R989E XXXYXXX +++++++++ •••••••••••••••• M 152.5 + 8~qF XXXXXXX +++++++++ ••• 4 •••••••••••• P @BSRE; XXXXX.XX +++++++++ •••••••••••••••• E .8F-Pf? XXXXXXX ++++++++++ ••••••••••••••• p I sees xxxxxxx ++++++++++ ••••••••••••••• A 150.0 + .espp .. XXXXXXX +~++++++++ ••••••••••••••• T ERees xxxxxx +~+++++~++ ••••••••••••••• U 8E1S@'8 XXX)(XX ++++++++++ ••••••••••••••• R I Fge-AE X )( X.X xx ++++++++++ ••••••••••••••• E 147.5 + ~epee XXXXYX +++++++++ EeRP@ XXXXXXX ++++••++++ •••••••••••••• Feess xxxxxxx +++++++~++ •••••••••••••• I • eSReP XXXXXXX .+++++++++ •••••••••••••• 145.0 + •• 6PS8E? XX)fXXX ++++++++++ •••••••••••••• •• _sespp ,XX)(XXX ... +++++++++ •• f:Fl8Eq )(XXXXX +++++++++++ ••••••••••••• t •• 8RPRP XXXXXX ++++++~+++ ••••••••••••• 142.5 + • a ee8B6 XXXXXXX ++++++++++ ••••••••••••• 8G1 986S6 XXX')(XXX +++++~+++.+ •••••••••••• •• ~Re8F Xyyxxxx. +++++++++++ •••••••••••• J • a PP8EE:XXXXXXX. ++++++••+++ •••••••••••• 140.v + •• ~eeRe x xxx x x: ++++++++++++ •••••••••••• 1 -----+------+------+------~------~------+------20.0 ?3.~ 2~.~ 3J.~ '4.0 3~.5 SYMBOL y •••••• 401.7417 795.1 r;11 ++++++ 795.1511 1581.9699 xxxxxx 1 ~81. QF1<:lq 2.36~.-':.1e7 PR8~P5 2.368.7887 ~1:;r:;.6'7~ .a"C'-~ ~155.6075 3549.0169 Figure 22. The Effect of Temperature and Moisture on the Die Pressure at a Constant Screw Speed of 45 RPM 62 CONTOtff-l PLnT r;r Tcr~pF:f'''T(JP~ VS. SCREW SPEEr) CCNTCURS ~F:'~ nYE Dpr-:-SStJ~ES C~NTClJR PLO T OF Xl")( 2 160.0 +XXXXXX)(XXXXXXXXXXXXXXXXXXXX; SCREW ~PEE~ SY~8CL y •••••• 344. 4135 ~67. 2702 + ..... +++ 367.2702 412.Q835 ~""II"" 50~. ~lO) 32,7.2.61CJ X)('(xxx 41~.qq~t') t\S 8.6969 eER€~e 453.6q6 Figure 23. The Effect of Temperature and Screw Speed on the Die Pressure at a Constant Moisture Content of 40 w/o. 63 dq dt 410 TEMPERATURE Figure 24. DSC Endotherm for Indium +=a (j"\ 400 Product J I Soyprotein CeK) 380 '- Texturized of I TEMPERATURE 360 Exotherm DSC 340 Figure 25. Typical - dq dt 65 CONTOUR rt CT flF "'E~l~CRJ\Tt'qE r c i v s , ~CREW Sr>EEr.> (RP~) C 0 ~ T oU f< S \ n '::: 1\8 ') C P n TIn NS (W / C ) , 160. a +X'(XX'C,o( <~,. +++++++++++++++ .. +++.f- ••••••••••••••••• 1 '~...... +++++++-+++++++++++...... 1 ~AR-8g~~9 x x x x xz x« x xxx x xx~< + ... -+ ++ -+ +++ +- +++ ++-+++ 155.0 ~ 8';; ~A=;";F~f=tF./X X:<;< x ~< '< )(x ~<:x x: y ...... 25.(-t:B45 27 • 7 () 1 t 3 L~7.:6l13 3 1 .91.649 <''( .'< '< ~/ ;< 31.94649 36. 1 :1 t 35 ~8~R8'1 ]{).13185 40.31721 40.31721 42.4-0988 Figure 26. The Effect of Temperature and Screw Speed on the Product ~bsorption at a Constant Moisture Level of 35 wlo • 66 CO~JT(JUR PLoT OF T!::-1!'s.:P/\Tt'ClE r c i V~. r~ntSTtJPF CCt-4TENT (W/O) C'lr"TGUP~ t\RC .\n~OPPTtONS (w/r-:) [~C"~T(-:UP PL':T OF Xl*X3 I 1 fj Q • 0 + :( X X v y ...... 22.12736 32. 55552 t- .. ~ .. 4- to 32.55552 .\. 1 • .:. t 1 83 '< XX '< ~~ ~~ Al.41183 50. 1~6813 EFA":'A8 50.2fS\.l13 59.12444- ...... 59.12.444 03.55260 Figure 27 . The Effect of Temperature and Moisture on the Product Absorption at a Constant Screw Speed of 70 RP~1 67 CONTOUR PLOT OF SCPE~ S~EED (Pf"'~) v s , r~()I$:tJRE CO",JTE~~T ('11/0 ) CONTOUR S ARE ~BSOhPTrON~ (~/a) CONTOlJP nLor or X2*)(3 110 .... 1 :) ') I ••• +++~++++ ••••••••••••••••••••••••••••• + .+ ++++++++ ••••••••••••••••••••••••••• ++ + f- + + + •••••••••••••••••••••••••• + + + + + ... • •••••••••••••••••••••••• I ..... +++++++++++ • • • •• • • • • • • • ••• •• • • • • • • • 9J + ...... ++++ ....+++ ••••••••••••••••••••••• XX +++++++++~+.++ •••••••••••••••••••••• 5 ~xx ++++++++++++++ ••••••••••••••••••••• C ~xxx +.++++ ... +++++++~ • • • • • • • • • • • • • • • • • • R ,XXXX ++++++++++.. ++++ ••••••••••••••••••• E 80 I.... ~x~xx~ +~+~++++++.++++ w ~x~xxx~ +++++++++++++++ ...... )C X)("( )C)()()(. ++ ...... +...... + .... +...... • • • • • •• • •• • •••• ~XXX~)(XXX +.+++++++++++~+~ •••••••••••••• I ~~~~~xxxx ++++++ •• +++.+~.~ ••••••••••••• c. 70 + xx~~~x~~ ... +++++~++++++++~ •••••••••••• Q, xxxx~x~x +++~~~~++++++.+~ x~~~~x~xx +++++++ ... ++++++++ ...... eF8 )( )( x )( x)( '(xx. ... ++ ..... + + + ...... + .. fa++ f I ReeS x~~xxx~xx .++~++++++++++.... + ••••••••• 60 + FEPB X)(XXXXX: MO T 5 TlJR E SYMBOL y •••••• 2g.63584 35. 97423 • ++ ++ + 35. 9 7~23 4~3.6~tOO 'J( XXXXX 48.65100 61.32778 €EA~F1~ 61.3277£3 7~ .00456 74.00456 aO.3~294 Figu re 2'8. The Effect of Screw Speed and Moisture on the Product Abso~ption at a Constant Processing Temperature of 150°C (zone II) 68 expansion was caused by the sudden release from elevated pressure at the die to atmospheric pressure and the flashing of the water vapor. Figure 29 shows the effect of temperature and the screw speed at a constant) initial moisture content of 30 w/o. The result indicated an area near a minimum; an increase in screw speed at low temperature produced a high and low bulk density. The relation of temperature and moisture on the bulk density is illustrated in figure 30. Increased temperature and moisture content increased the bulk density, because high temperature produced the flashing of water vapor, which increased the expansion. As previously mentioned, it was desirable to maintain a low enough temperature at the die to prevent the product from overheating, yet high enough to enable sufficient heat to be added to cause proper fiber formation. The die temperature was set at SOoC. The actual temperature was greater; the dies used were not equipped with a cooling system allowing an increase in temperature due to mechanical friction and chemical reaction. The actual temperature of the die was taken as a dependent variable of the product temperature. Response surface analysis plots are shown in figures 31-33. 69 Cn~JTCUP PLCT CF -r:~~PER,\Tt'RE r c i VS. SCRr=\-j 3rr::::: f) (CP~) CC~~rOUf'S \PE 13ULK OE";S1TiES r5/C() I 160.0 +W3 .~~e xxxxxx ~~++++~~~+++~+•••••• ~++~+~+~~~+++~ ~ ~ ~ _ R ~ F ~. ~ X. XXXXX ++++++++++++.~+~~+++~+++~~~~.++4~ ~~~ &8P~ ~xxxxx ++++++++~+++++++++++~++++++~++~+ · I ~~~.eeFg ~xxxxx, ++++++++++++++++++++~++++~+++~' y 157.5 + •••.pcEAe XXXXXX ++ ..+++++++++ .....+~ ...... ++++++++++++ .~y ~'-II .F9S8Q XXXXXX ++++-++++++++-+-+++++++... +++~+ .. ~+ xx .~. f;f=oEF8 XX XX X X ...++ ..... + +++ ++++'-++ +- + ++ +++++ + + ~.... x;·- x .~~ A@eeR XXXXXX ++++++++++++++.+++++++++++++ ,xxx I q9f;~. xx).~x 155.0 ...... XXXXXXI +++++++++++++++ ... ++++++++++ 11K ~F-_.e-A. iO(XXXXX' + ... +++...... + ...... ++ ...... + ... + )·XY;<. T ~~ PBeF xxxxxxx +++++++++++++++~+++~++~+++xXXyv ~ f ,,~ Ee~ep x xx xx x x: ++++++++++++++++++++++++++ ~XYY~';·· M 152.5 +~~ FEq~_ XXXXXXXX ++++++++++++++~~+++++++++ YVYXYX p . ~ .. e~p_.. ~ XXXXXXXX +++++++++++++++++++++++++ VYYXXX E • fTFU?& XXXXXXXX ++f-+ +++++++.+++ ... --4-+++++ ....+++ : --I. I -+...... -....+...... --+-----+---+~+...... -+...... -+------+---- r 1C" "Q C .... -S I ro ~t ~o W ++++++++++++++++++++++++ 0" .0 •01 + ++++++++++++++~+~+U~~~~~~~ Z ~++++++++++++++ ~~~~~~~XXX~ ....-4 I +.++++++++++ XXX~XXxxX~XXX~XX am (j') ri" --I 11)( +. (J) t ++++++++++ KXXXX~~XX~XXXXXXXXX~ C~ ~++++++ x~XXXXXXXXX~XXXxXXX~XXX ~ '"0 ::J::r •II rnX -< !\)I ;.01) ro m m :ll )( +. ~ Wi ++++ XXXX~XXXXXXXXXXXXXX~XX~XXX 0 L1;T1 m ,~X> CO~jTCUR r-i.nr GF TEMryEPI\T'JRE (C) 'Is. ·SCREW SPEED (RPM) CONTOURS ~Rc ppa~UCT TEMPEP\TU~cS (e) CONTCUR ~LOT OF Xl*X2 I 160.0 ++++++ XXXXXXXXXXX/~ qp~~A~~cpopqc~e~ ~.~~.~~._w.. ~ ++ ++ + )(X)t':(X. X;(XXX'(X 4?~~.... A+=1~Q~c.~q~,=-=~c... ~ ••«.IIII.JII • .II1 .+++++ xxxxxxxxxxxx BB€AR€~~BA~8~E~~~ ~~.~~~~R~_ 1++.+++ ~xxxxxx~~xxx FC8~RQ68CAQq~Q~AC ~1.~~R••• 15?5 ++++++++ xxxxxxxxxxxxx 88e~~~8c~Qa~c~~F~Q I~ ••• ~I +++ xxxxxx.x:<: scpr-:'fi SO"=:~!') SYMBOL y •••••• 66.91517 71.02899 .+++++ 71.02819 7?25662 xx xxxx 79.25662 87.481\25 c;eq~AA 87.4q425 95.71188 ~~~~~. 95.71183 - 99.62570 Figure 31. The Effect of Temperature and Screw Speed on Product Temperature at a Constant Moisture Content of 27 wlo 72 TEMPt:R~TlJPr: 1~(1t:STURE CONTOlJR PLOT OF r c i 'IS. c ourer-r (\I/O) CONTOURS ~PE PRGDlJCT "'F~~nEP~iUPES r c i , CCf'4TfltJP f'LCT SF XlftX3 160.v + ..qeee 1.lmlll.... I".I.IIIII""'11.~ .€~8.c;~t:; YVYYX A€EPE .•R.~R~•• I.I~R~R.~.~ PFQcc~q .~yvXX qeeqae •••••••••• I.W.~~. q~Q~~G~~ xxxxxf t QE6e~Ee ~ R~ •••••• I.R~ ••R CCCP~~Q~~ Xyxxx+ 157.5 .... gaeSARgRR ••~ •• ~ ••a •• _eR~QQBQQg'XXxxx~. 8AESA8E9S9 ~ ••~IWW ~e~g~~q~9~ XXYXy~+ geee~Eeef1~e . ~GQ';~QBA~~;:;g ~xxx)('+1++ ee"~8E-6.c;8Be-eBt:1E~A€~€-Ac;~~~-E.c:; XXYXX:l.f++ I E.g~A.g~cA~et;e.pe~PFt?RF ~~€;gQ~QR e~ 155.0 + , ;< ''.X Y)f :(i+'"+ X eAP8€qQAqFFR6AR~~e~g=c~~~=c~ .xxyxxx/++~ T , X :Eee{;€.13f;-E1=16~8-&EBE,,=€r;€~·~Ee-Et:; ~ X:< if XX X/+" + + E XX qpeeeESpe8PG8~e~F4q~ggqq~~ xxxxxx~~+++ M 152.5 + XX e€€€e&e~e~8€A~eAE~€~· ;(XYXXXx,t.++++ p XXX G68e'3e;::"'~PR~Q86RASqC;84?':; .xxxx'(xxj...... E ~~x ee€~€eBeeeBg~€e~pe~B~~E ~xxxx~~++~++ q xxxx Aeq8~89pPA8~AF8~9Qq~f= .t·(XXX~('1'.( ++-+++ I e6-e.;;.geEAA8~~-E€eR.g+::B~-A A 150.0 + )( X X X ... :" X X :< X X X ',+",,,"''' .. T xxxxx ~~~g~e~R6Rq~~F88~8q X~XXXXXXt+++++. u X)()(XX €e9B~.e8€e€QE€A-Ae:;;~~ X~'(XXXY'('/"'++~+-+-. ~ X)()()( XX Re~9E8~6eReFg~ ,,-=log X X <'t X v y X y' ~+- of- +- .. + • I '()(~)()( 8RBA..g+:;ee€..g~A-e~ F: 147.'5 + '( X X X:'( )( X '( X: ++ + + +- .... XX))(XX Fe88ggAe~EEq~8~ xxxxxxxxx ..++~+ •• )()( )C ~ '( X X €-EAePE6€fl~€f=tFA'; .:< X X;.< X )( X X y • ++ .. +- ..... )()()C:x)( XX 8FRfH3A88pe~~s~. X X X X X .'< X X X ~ + ++ + ++ •• I .E-A~eaE~6f;Ae~ 145.0 + X)r"}('fX)(X .)(XX' MOISTU~E SYMBOL y •••••• 82.€Sq87 - ~'5.1q520 ++++++ a5.19~20 90.26586 X:< x X)(X 9.).~65AF) - 95.3365~ g-Ase€e ~S.J~652 - 1 0 .) • 40"" 1 q ~".1"~. 100.~~07t8 - 1 ('2.9425 1 Figure 32. The Effect of Temperature and Moisture on the Product Temperature at a Constant Screw Speed of 135 RPM 73 CONTOUP PLOT OF SCPEW SP~~D (PP") "J. MnT5T'JRE COf'~TENT CW/O) C~tITntJP<; ~PC: DP~DUCT rE~~flER\T'.JPES (e) 11 0 + 1 u,J I.. ABAAS Ra •••• R.R~~~~~~~~.~~I~~~R. -c~~q~~~ ~ge68 .WWR~~~~•• ~.~~.~RI~~RI8.R ~~~c~Ba~ EeaE€e~ 1 ••••I •• III~I~~I~R~I~8~1 ~~~~P86a .c;+:; 43 e € ~ ;;_ .. a.. JII. II• I • III IIJI" ...JlIIIII,. ~ Jt Q C C OR £; t?,Cf I 8~@REe88 .~ •• ~ ••• ~al~~3~~~~I~ ~G~9~~~8Q 90 + ReFee~~~F ~~.R~.W~.I~~~~.~~~ ~~AA=~8~~~ PB·~Be~~RRI=;~ ••• a~.. 311~~ ~~ ~ _J11 ~ _J~~t.:.c;~~-C.G+=.c~ s ~6AeBBeeeEee 1.11~IR.I. ~~cEFA~~&8~pg C . eee€t3AeeaE6et;p...:; ... ,.. ~gc=;~ a€~E€~6RA~Q R I x ~~€~~~e~~@~~~e8GQE~AAeg~FP~cc~~~FCC~Q~q 8J + x EAPReeAgqqAe~~BeeA~QC~~AqQ~~~~~~RP w XX' Ee@€€Be8AAB6~8B~€e~E~~~Bp~~~~c~SP8CA xxxx ~~~e8EA~&8eReq~~qe~qqqF8~~S~qc~~QQx s .~ xxx X €€E43-E€-':-F6-8€~~8€qeA~-E~.c;~+=.c4::EC~::;8. x 'I.. P X XX X X X .c:8 ~ep :::;C,PA.Q~l;FcP6=1qQQ~O~oS =:~.q 8::J X v:~ E 70 I+ xx x ~ X)( '( .g~6-e~-e6.e~~f=Al?.c;R~~.cCCO€~~C~, X y ~" ," E >c: SYM80L v •••••• S6.26426 60. 76·)4.1 .... +++ cu.76u41 - 69.75270 )(XXXXX f,q.75':'-70 - 73.7·":~99 EEqFee 7'3.74499 - 87.73728 "",~ ... 11I .. 87.73728 - 92.23342 Figure 33. The Effect of Screw Speed and Moisture on the Product Temperature at a Constant Processing Temperature of 1400 C (Zone I I ) Chapter 7 DISCUSSION The results of SEM and the analysis of variance prove that it was possible to produce different product characteristics. Texture, which is a product of var t ab l e s ' interaction, can be manipulated by controlling the process variables. As expected, extrusion rate was primarily a function of screw speed. Increased screw speed increased the quantity of material passing through the die. Analysis of variance shows that moisture and temperature also had a very significant effect (P~O.Ol-table 6). This trend was probably related to flow characteristics of the feed material. Increased dough moisture resulted in lower bulk density and greater percentage water absorption. Increased moisture content produced a certain degree of swelling (caking) of protein molecules, which caused the decrease in flow rate. An increased temperature enhanced the swelling effect. It was not known to what extent water absorption could be taken as a measure of the degree of swelling of protein molecules [65,66J. Extrusion -rate at high screw speed was also a result of pressure gradient. The pressure profile indicated the location of maximum pressure, which was greatly dependent on Table 6 Effects of Variables on Extrudate Characteristics LEVELS OF SIGNIFICANCE VARIABLES Extrusion Die Bulk Absorp- Product Rate Pressure Density tion Temperature Temperature ~ 0.01 ~ 0.01 NS NS ~ 0.05 Screw speed ~ 0.01 ~ 0.05 NS ~ 0.01 ~ 0.01 Moisture ~ 0.01 ~ 0.01 NS ~ 0.05 NS Regression 88.3% 89.8% 14.0% 53.89% 74.26% (P~O.Ol)(P~O.Ol)( NS ) (P-,O.Ol) (P~O.Ol) ...... (Jl 76 operating conditions, such as barrel temperature. flow rate, frequency of screw rotation, screw geometry, and moisture level [71J. In general, minimum pressure drop across the ribbon die orifice ranged from 300 to 500 psi, which was almost twice as much as the conventional method. The pressure trend was difficult to establish. Increased screw speed did not always increase pressure. This variable was related to the viscocity of the molten material in the die zone. As temperature and moisture increased, the viscocity decreased. and the less viscous material flowed out faster, so that pressure decreased. 11 The fiber die runs had a small die orifice (0.020 ) and generated a higher pressure range (1000-1600 psi). This indicated a higher friction in the land of the die. Too high a die pressure was very significant for fiber formation. An optical micrograph of the extrudate at too high a pressure showed no fiber formation; the product was tightly compacted, very dense and had very little rehydration value (figure 34). After the die was disassembled, fibrous structures were found in the reservoir section. It was apparent that the high pressure, which produced high shear strain and back flow, disrupted the fibers. Fiber formation began in the screw channel. The shear strain in the screw provided a good environment to align the protein molecules during their flow. Therefore, increased shear rate increased the possibility for chemical reaction 77 Figure 34. Optical Micrograph of Fiber Die Runs, 12X Figure 35. Scanning Electron Micrograph of Run.F4 shows Porous Structure, 700X 78 and produced texturization. Fibers were further formed and aligned in each consecutive heating section. The final texture of the extrudate was a result of all these reactions. The final extrudate seemed to remember the formation in the screw section by showing interlaced fibers. Analysis of variance gave an indication that all process variables, temperature, screw speed and moisture had a very significant effect on the die pressure (table 6). The result of Differential Scanning Calorimetry showed an e ndo t her a i c curve without a peak. This was expected because soy protein undergoes an irreversible reaction and behaved more like a dough. DSC analysis might not be an appropriate method for characterizing soy protein texturization. Furthermore, layers of the fibers were easily separated along the direction of orientation. High temperature produced a lateral fissuring to such an extent tha t they had a weak 1i nk , Probabl s , the soy protei n wa s only a semicrystalline or amorphous polymer. Product absorption showed a decrease with higher feed moisture, and an increase with higher process temperature (figure 27). At lower temperature the product was uncooked, tightly compacted, and very dense. There was very little penetration of water during rehydration. As the product temperature increased, the product was more structured (fibrous), cooked and spongy, because upon exiting from the die, the product expanded, becoming more porous and less 79 dense. Figure 35 reflects the microstructure which shows larger cavities and smaller filaments. The microstructure illustrates that some of the tight fibrillar arrangement observed at the die were lost due to sudden expansion. The more spongelike the structure the more water will be imbibed in the product. ~igh screw speed not only reduced the heat exposure the protein received but also produced interlaced fibers. This structure tended to trap the expanding steam within the product when it left the die. This also elevated the v;scocity of the dough, and reduced product expansion as it left the extruder. Thus, it was less porous. Table 6 shows that the absorption value was mostly governed by screw speed and moisture content. During the rehydration period, the protein did not disintegrate or lose its structure and shape. This proved that the protein denatured or changed its physical-chemical and functional properties due to heat processing. The extrusion process caused most of the water soluble soybean protein to break into subunits and/or become insoluble. Thus, heat and moisture caused progressive insolubility of the protein in soybean meal [34,72]. A high pressure gave higher extrusion rates and, in effect, increased the rate of shear, which resulted in better cohesion and better retention of structure on rehydration. Work done by Taranto et ale showed that fibers formed at higher screw speed 80 extrusion are stronger [5]. Theoretically, the passage from die to atmospheric pressure is characterized by "puffing", which controls the product bulk density. This is mainly due to flashing-off superheated vapor and to the release of normal stresses. As the material cools, it sets into a definite porous structure with a slight size reduction. There is no significant correlation between the variables on the bulk density. Perhaps, it is related more to the die temperature. Even though density changed quite markedly over the range of temperature, width and thickness remained constant (average degree of puffing was 40%). This suggests that all physical changes occured prior to final extrusion. Temperature increases were not only found in die temperature but also in the heating zones (figure 36). It appeared that there were substantial heat sources other than the heating element. The increased temperature came from the mechanical work and frictional heat in the screw section and in the die section, where the shearing action existed; the dough temperature might be even higher than the desired temperature. Exceeding a floor temperature was necessary to provide sufficient energy for denaturation. The thermal denaturation of aligned protein molecules to form cross-link layers is an irreversible endothermic chemical reaction in the extruder 81 > L&.I !J z /1 0 : I N : / I I I > I LIJ z Vl 0 QJ : I c: N 0 / N . rn / c: , -r- . I +J ct1 : I QJ :', - :r: - +oJ - c: I QJ LIJ S- QJ Z 4- 0 C+- ...: / .r- N -0 : / ....., .. ~ / cu r-- -~,. / 'r- •e: 4- 0 / - 0 .- ," - S- .-.. I 0- C QJ " " &1.1 S- 0 :::3 U Z +oJ • ., 0 ct1 0 .. S- 65 N OJ CI c: C- c 0 E ;: .a ... '\" Q) ..., ~ ..D• ~ ii Ii: y-. C'l en c: Vl \ Vl QJ I U 0 I&J S- I \ z CL. I 0 \ N (.,0 . (V') \ QJ S- :::3 en .r- U- 0 0 0 ti) ~ 4D aJnl~Jadwal J o 82 behaving as a reactor. Figure 37 shows the dependency of residence time versus screw speed. Increasing residence time would provide an environment giving a greater degree of thermal denaturation. Zuilichem noted that residence time distribution controlled the degree of mixing and the degree of uniformity of the strain exerted on the dough [63]. In the MTE system, residence time was increased by the addition of the conditioner zone, this was about 5-10 minutes longer than the conventional extrusion. Extrudates obtained at lower than 40 RPM and higher than 100 RPM demonstrated the erratic behavior of the extruder. This study indicated that shear values decreased as the initial moisture content increased, but above 40% there was virtually no influence of moisture on texture. Also, at lower moisture content (less than 20%), no interaction was observed between shear value and process temperature. Observation of the physical appearance of the products indicated that as temperature increased, orientation and fiberization increased. The scanning electron micrographs revealed alterations in physical structure during processing. Figure 38 shows the appearance of fibers among unstructured globular protein of run Gl (zone II-160°C, 30% moisture, 40 RPM) at lOOOx magnification. Figure 39 shows the exellent fibrous structure of run F3 (zone II-150°, 40% moisture, 80 RPM) at 150x magnification. An isolated fiber 16 83 RUN$ ZONEII EJ C 140·C 14 & ----F I~OoC 0 ._....-.. 160·C 12 ,.. c -:2 o• ,, LtJ .,, 2 ., I-- , •, 10 •... I.IJ \ (.) .. Z l. 9 lIJ 9 Q ... -en •. LtJ •... ~ •... ..• .•., 8 •• ••• ~. o•..•. .• .- •-. •• ~t -·-... ~0...... ••• • .... ~ . 6 ..... 40 8 SCREW SPEED (Rpm) Fi gure 37. Res i dence Time versus Screw Speed 84 Figure 38 Scanning Electron Micrograph of Untexturized Soy Protein with Strands of Fibers, lOOOX Figure 39. Optical Microscope of Fibrous Structure of Run F3, 150X 85 from figure 39 was shown in figure 40 (4000x). Finally, figure 41 shows the fibers of run 13 {zone II-160°C, 35% moisture, 80 RPM). The limitation of this observation was the unavailability of mechanical apparatus to measure the quality of fibers on breaking strength, shear» or "c he w", Also, the results were equipment specific. Larger scale experiments should have an increase effect of temperature and more complex non-Newtonian flow behavior [73]. 86 Figure 40. Scanning Electron Micrograph of an Isolated Fiber of Run F3, 4000X Figure 41. Scanning Electron Micrograph of Run 13, 1000X Chapter 8 CONCLUSIONS This study described the importance of controlling the shear environment in the screw and die, the dough temperature, and the residence time to produce varying texturized extruded products of soy protein. The results indicate the formation of fibrous layers. A summary of the study follows: 1. Soy protein was continuously extruded by the MTE process. 2. Controlling the shear rate and the flow rate through the screw and the die was important in cantrall ing fiber formation. Too high a shear rate at the die wall disrupted the fibers. 3. Increasing the shear rate and the residence time (5-10 minutes) tended to enhance cross-linking between protein. 4. The extrudate characteristics were highly dependent on screw speed and temperature. 5. The operating pressure and extrusion rate were dependent on the temperature, moisture, and screw speed. 6. Process conditions were altered as a result of a longer assembly line than in normal extrusion; pressure drop 88 was increased from 300 to 1500 psi and residence time from 5 to 15 minutes. 7. The product absorption was dependent on screw speed and initial moisture content. 8. Product temperature was found to be a function of the zone set temperatures and screw speed. 9. Dough temperature. was higher than the process temperature due to the lack of a cooling system and heat generation. 10. Plugging of the die to increase pressure was not feasible, since the resultant prolonged cooking time would cause degradation. 11. Optimum operating conditions to a produce fibrous texture were found to be a temperature profile of 160-135-1100C, 80 RPM, and 40% moisture for the equipment used in this study. 89 Chapter 9 RECOMMENDATIONS 1. The use of a cooling system would provide better control of the dough temperature, resulting in better control of bulk density. Frictional heat due to mechanical work usually builds up at the screw section and the die land. 2. The use of mechanical tests to evaluate the f i ber s ' quality, such as: shear force - Warner-Bratzler shear, shear force and work - Kramer Shear Press, (firmness and crispness) texture measurement - General Food Texturometer, and breaking strength - Instron, Model TM. would yield better evaluation. 3. Extrusion should be attempted at lower temperature gradients. 4. The feed system should be modi fied for better control of feed ra te. 5. Horizontal extrusion causing a higher deformation would produce better fibers. 6. Extrusion with the Leistritz twin screw extruder should be attempted. Good shearing, flow control, and controllable feed rate in the twin screw extruder will provide a better control of the final texture of the 90 soy protein product. 7. Higher die temperatures should be attempted. 8. Further study is needed to determine if soy protein crystallization is affected by the independent variables. 9. Computer simulation should facilitate better control of the pressure, temperature, and screw speed. BIBLIOGRAPHY 1 • J• Ra k 0 sky , J• ~ • F0 0 d ~~!!!., Vol. ~ , p • 1a05 (1970). 2. J.R. Collier, Research Proposal to the National Science Foundation (1983). 3 • J. ~1 •Ag ui 1era and F. V. K0 s i k 0 Wski, J. £.!. F0 0 d Sci., Vol. il, pp. 647-651 (1976). 4. T.J. Maurice and D.W. Stanley, Canadian lnst. Food Sci. Te c hn 0 1. ~., Vol. .!.! ' No.1, pp. 1- 6"--TJ an:-r9 7ar:- 5. n.v. Taranto et al., i. of Fo~~ ~.i., Vol. 40, pp. 1264-1269 (1975). 6. J.M. Aguilera, F.V. Kosikowski, and L.F. Hood, J. of Food ~!., ~l. !!.' pp , 120 9 - 1 2 13 (1 9 76 ) • - 7. W.J. Wolf and F.l. Baker, Cereal Sci. Today, Vol • .!1., No.5, pp. 125-147 (May 1972). -- 8 . W.J. Wolf and F.L. Baker, American Assoc. of Cereal Chem i s t s , Vol. g, pp. 38 7- 3 96 (I g-1"s-) • 9. J.L. Ko k i n i , J.B. 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Repholz, in Food Pharmaceutical and Bioe~~erin,[ 1967/ll, ed i te APPENDICES APPENOIX A 97 Table 7 Die Temperatures ======CONDITION TEMPERATURE (C)* SPEEO* MOISTURE Die CODE ZONE II ZONE III ZONE IV (RPM) (w/o)* Temp C ======Al 140 115 90 40 30 67.5 A2 140 115 90 60 30 78.3 A3 140 115 90 80 30 88.3 A4 140 115 90 100 30 90.0 81 140 115 90 40 35 75.0 62 140 115 90 60 35 80.0 83 140 115 90 80 35 85.0 84 140 115 90 100 35 90.0 Cl 140 115 90 40 40 65.0 C2 140 115 90 60 40 75.0 C3 140 115 90 80 40 75.0 C4 140 115 90 100 40 79.0 Dl 150 125 100 40 30 78.6 D2 150 125 100 60 30 79.0 03 150 125 100 80 30 86.7 04 150 125 100 100 30 95.0 E1 150 125 100 40 35 50.0 E2 150 125 100 60 35 75.0 E3 150 125 100 80 35 100.0 E4 150 125 100 100 35 100.0 F1 150 125 100 40 40 75.0 F2 150 125 100 60 40 75.0 F3 150 125 100 80 40 80.0 F4 150 125 100 100 40 90.0 G1 160 135 110 40 30 80.6 G2 160 135 110 60 30 88.6 G3 160 135 110 80 30 94.3 G4 160 135 110 100 30 100.0 HI 160 135 110 40 35 80.0 H2 160 135 110 60 35 91 . 7 H3 160 135 110 80 35 95.0 H4 160 135 110 100 35 92.1 I 1 160 135 110 40 40 75.0 12 160 135 110 60 40 82.5 13 160 135 110 80 40 90.0 14 160 135 110 100 40 90.0 Note: *Zone I was unheated, and Zone V was heated to 50 degrees Celsius. Table 8 98 Flo:w Rate s CONDITION EXT.RATE* VO[.RATE CODE (in/min) (in3/hr) ======Al 20.5 -+ 2. 7 38.4 A2 33.7 -+ 1 . 5 63.2 A3 37.7 -+ 3 . 1 70 . 7 A4 44.0 ± 1.8 82.5 B1 24.0 ± 0.5 45.0 82 23.7 ± 3 . 1 44.4 83 33.3 ± 0.9 62.4 84 44.1 ± 4 . 1 82.7 C1 19.0 + 2.8 35.6 C2 29.0 -+ 2.9 54.4 C3 32.2 -+ 3.2 60.4 C4 34.4 ± 3.4 64.5 01 24.0 -+ 2.5 45.0 02 22.3 ± O. 7 41.8 03 31.0 ± 3.8 58 . 1 04 44.3 ± 2.4 83.1 E1 7.5 ± 1 . 2 14. 1 E2 16.5 -+ 2.2 30.9 E3 21.6 + 4.1 40.5 E4 33.2 + 3.8 62.2 Fl 12.9 -+ 2.6 24.2 F2 23.8 -+ 1.3 44.6 F3 24.0 + 1 . 7 45.0 F4 27.1 + 1 . 7 50.8 Gl 20.6 -+ 1.8 38.6 G2 27.9 + 2.5 52.3 G3 30.8 + 2.2 57.8 -:;: G4 45.7 - 4.1 85.7 HI 18.6 + 1 . 5 34.9 H2 27.3 -+ 2.3 51.2 H3 31.7 -+ 2 . 7 59.4 H4 42.9 -+ 3.2 80.4 11 13.2 ± 0.3 24.8 12 24.8 ± 3. 1 46.5 13 27.7 ± 1.4 51.9 14 28.9 ± 4.0 54.2 *90% confidence 1i mi t 99 Table 9 Pressure Profiles ======CONDITION P R E S S U R E* ( psi ) CODE barrel die drop ======Al 2742 ±124 1442 ± 45 1300 ± 85 A2 2608 ± 45 1350 ± 70 1258 ± 58 A3 2300 ±183 1150 ± 76 1150 ±.130 A4 2075 ±109 1068 ± 75 1007 ± 92 81 864 ± 44 543 ± 42 321 ±. 43 82 943 ±177 543 ± 42 400 ±. 80 83 978 ± 36 629 ±. 25 350 ± 31 84 1043 ± 73 621 ± 52 430 ±. 62 Cl 1207 ±332 664 ±281 528 ±300 C2 985 ± 35 543 ± 36 372 ±. 35 C3 980 ±116 480 ± 68 420 ±. 48 C4 900 ± 50 450 ± 45 460 ± 23 01 1885 ±216 1157 ± 73 729 ±145 02 1767 ±146 1150 ± 76 617 ±.lll 03 1571 ±103 864 ±153 773 ±128 04 1400 ±320 793 ±260 575 ±290 E1 680 ±213 310 ±111 270 .± 16 2 E2 857 ±266 546 ±142 341 ±204 E3 1000 ±.100 550 ±. 50 470 ± 25 E4 1030 ±194 530 ± 75 550 ±135 Fl 540 ± 83 450 ± 87 80 ± 85 F2 550 ± 76 441 ± 73 108 ± 74 F3 558 ± 73 425 ±. 55 133 ± 64 F4 557 ± 86 393 ± 49 170 ± 45 G1 1729 ± 45 950 ± 38 779 ± 41 G2 1914 ±164 1012 ± 29 854 ±. 96 G3 1800 ±141 900 ±130 900 ±136 G4 1714 ±155 785 ± 99 917 ±127 HI 1120 ±117 710 ± 66 410 ±. 92 H2 1071 ±.103 614 ± 35 457 ±.. 69 H3 1121 ± 99 586 ± 44 535 ± 72 H4 1150 ±. 60 560 ± 60 589 ±. 60 I 1 720 ± 24 470 ± 25 250 ± 40 12 600 ± 50 363 ± 13 238 ± 10 13 529 ± 70 321 ± 59 209 ± 65 14 479 ± 36 300 ± 38 179 ± 37 *95S conffdence limit Table 10 100 Extrusion Characteristics ~~--~--~-~~~~-~~----~~-~-~~-----~~------~-~~-~~-~-~---~-~~-----~~--~~~-----~--~~~~-----~ CONDITION ABSORP Bulk den. CODE TION(w/o) (glee) ======Al 63.8 1.49 A2 47.8 1.53 A3 33.8 1.58 A4 33.5 1.66 81 25.9 1.54 82 25.8 1 . 51 83 25.7 1.46 84 27.5 1.53 C1 33.5 1.78 C2 33.9 1.54 C3 30.9 1.82 C4 30.5 1 • 79 01 45.8 1.56 02 39.4 1.58 03 32.5 1.61 04 26.8 1.66 E1 56.3 2.56 E2 47.5 1.70 E3 33.0 1.48 E4 30.0 1.59 Fl 39.3 1.49 F2 33.5 1.54 F3 30.3 1.54 F4 22.5 1.61 G1 39.9 1 . 71 G2 34.5 1.66 G3 34.5 1.60 G4 30.9 1.67 HI 28.0 1.64 H2 27.5 1.59 H3 27.3 1.58 H4 32.4 1.57 I 1 27.0 1.65 12 31.0 1.62 13 35.5 1.57 14 20.3 1.56 101 Appendix B FILE: c sj- r r S4S A //H4J5eCS~ JOB (. // H6617~P~t15).XCSHll.PLPT // EXEC 5-S •*------RESpnNsE SUPF.rE ANALYSI3------* THE QE5PCNSE SUPf=ACE AN·,\l.Y51 s -~s nr:pror.-~~D eN SOYBEAN PPOTEIN EXTTPU5TQN IN ~ELT Tn.NSF~RM_TtON EXTRUSICN PROCESS. T~E 08JECTIV~ WAS TO OIscaVEP WHIC~ FACTOR VALUES (INDF~ENnENT VAPtAAL~~l OPTIMIZE A RESPONSE. 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