Texturization and Gelation - American Chemical Society

8 Heat-Stir Denaturation of Cottonseed Proteins: Texturization and Gelation 1

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 14, 2016 | http://pubs.acs.org Publication Date: December 13, 1982 | doi: 10.1021/bk-1982-0206.ch008

JOHN P. CHERRY and LEAH C. BERARDI United States Department of Agriculture, Southern Regional Research Center, Agricultural Research Service, New Orleans, LA 70179 The developments of glandless, or gossypol-free, cotton (1, 2, 3,) and the liquid cyclone process (LCP) (4, 5) to mechani c a l l y extract gossypol-containing glands make it possible to produce edible vegetable protein products such as flours, concen trates and isolates from cottonseeds (6-11). An enriched bread containing toasted glandless kernels i s presently marketed i n selected areas of the United States under the trade name of "Proteina" (12). Spinning and thermoplastic extrusion processes were applied to further expand the potential u t i l i z a t i o n of cottonseed as texturized protein products (13-22). Berardi and Cherry (23) developed a simple heat-stir procedure to produce texturized pro ducts and self-sustaining gels from glandless cottonseed protein isolates. Water suspensions of c l a s s i c a l and storage protein isolates at pH's of 4.5 to 9.0, were heated to 90°C with stirring. Texturized products having the mouthfeel and chewiness of cooked meat were formed. Although methods are available for texturizing vegetable pro t e i n s , there i s limited information on the changes that proteins undergo when they are converted to texturized or gelled products (22, 24, 25). During the spinning and thermoplastic extrusion processes, moistened vegetable proteins are fed into an extruder, mixed and heated. Data suggest that during these processes, the polypeptides in the proteins hydrate, gradually unravel, become stretched by the shearing action of the rotating screw flites and form new cross-linkages which result in fibrous structures. The heated plasticized mass is forced through a die at the extruder discharge to form expanded texturized strands of protein with meat-like characteristics. Rhee et aj_. (24) showed that texturized fibers formed from raw ingredients at acid pHs had stronger physical properties, rougher surfaces and smaller diameters than those made at alkaline pH. Proteolytic enzyme modified proteins containing mainly low molecular weight polypeptides could not maintain textural integrity upon hydration and retort heat treatment. 1

Current address: United States Department of Agriculture, Eastern Regional Research Center, Philadelphia, PA 19118. This chapter not subject to U.S. copyright. Published 1982 American Chemical Society.

Cherry; Food Protein Deterioration ACS Symposium Series; American Chemical Society: Washington, DC, 1982.


164

FOOD

PROTEIN

DETERIORATION

High NaCl concentrations interfered with, while CaCl2 enhanced, the texturization processes. An understanding of the mechanisms involved in the changes of protein produced consistencies (or relative viscosities) during the formation of textured or gel led products at varying protein concentrations, temperatures and pHs is important in advancing the formulation and processing of aqueous food systems. This chapter examines the consistency changes, i . e . , thixotropism, gelation and t e x t u r i z a t i o n , of various aqueous suspen sions of cottonseed protein products during the heat-stir process (23) under varying conditions of concentration, temperature and pH. The C. W. Brabender Visco-Anrylo-Graph, developed, as one of i t s functions, to continuously measure the consistency or relative textural changes of starch pastes during cooking and cooling (21, 26, 27) was extended to studies of similar changes with cottonseed protein products i n aqueous suspensions. Experimental Procedures Preparation of basic protein materials* The protein products tested or evaluated included LCP, glandless and a i r c l a s s i f i e d hexane-defatted cottonseed f l o u r s , concentrates and i s o l a t e s . Glandless cottonseeds from the varieties Acala, Gregg-25-V and Watson GL-16-A were flaked, hexane-defatted and desolventized under laboratory conditions that included no heat treatments. Watson GL-16-B and Watson GL-16-C flours were prepared by commercial p i l o t plant operations which included heat in the desolventization step. The Watson GL-16-C flour was heated further to reduce i t s bacterial count and moisture content (28) . The Acala flour was further processed by a i r - c l a s s i f i c a t i o n into five fractions with a Pillsbury Laboratory Model No. 1 Unit (29) . The f i r s t and second separations, which contained the smallest sized p a r t i c l e s , were combined and labeled as the fines f r a c t i o n . Separations three and four were combined as the coarse f r a c t i o n , and f i v e , consisting mainly of debris, was discarded. Two glandless cottonseed concentrates were prepared as follows: 1) double extraction of the Acala flour with water (H2O, H20-extracted concentrate), and 2) extraction f i r s t with 0.008 M CaCl2» and then with water (CaCl2> H20-extracted concentrate). The resulting concentrates were dried by l y o p h i l i z a t i o n . The c l a s s i c a l isolate (CI) (30) containing both nonstorage proteins (NSP) and storage proteins (SP) was precipitated at pH 5.0 from a 0.034 Ν NaOH extraction (pH 10.5) of Acala f l o u r , washed at pH 5.0 and spray-dried at pH 7.0. The NSP- and SP-isolates were prepared by the selective precipitation procedure (11). In sum mary, the pH of the 0.034 Ν NaOH extract (pH 10.5) was lowered to 6.8 to precipitate SP which was then water-washed and spray-dried at pH 6.8. The remaining whey was then adjusted to pH 4.0 to precipitate NSP, which was then water-washed at pH 4.8 and


8.

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BERARDi

Cottonseed

Proteins

165


spray-dried at pH 5.1. A l l of the dry protein products were ground to flour consistencies in an Alpine 160 Ζ Kolloplex pin mill. Proximate compositions of the cottonseed protein products are presented i n Table I . Analysis methods. Proximate and amino acid compositions of cottonseed protein products were determined with established procedures (31, 32, 33). Meat loaf products containing 0 to 50% textured CI and SP-isolate were prepared by a basic recipe as outlined by Berardi and Cherry (23). A 10-member taste-panel compared cooked meat-loaf products with and without textured cottonseed proteins on a scale of 1 to 4; the al1-meat product was a r b i t r a r i l y assigned a value of 4.0 (23). Chemical modifications and additives. The LCP-flour in water was chemically modified by succinylation and acetyl ation according to the method of Beuchat et a U (34). The anhydrides were added to the protein suspensions in equivalent amounts varying from 2.5% to 80% of the protein weight in the f l o u r . At 1% by weight concentration, CaS04, soybean flour and concentrate, soluble starch, Toruway -49, -42 and -30 (yeast proteins), sodium alginate, wheat gluten, casein, cysteine-HCl, raffinose, sucrose, glucose, gossypol, NSP and c r y s t a l l i n e eellulose were added alone or in various combinations to selected cottonseed protein suspensions prior to the texturization studies. Other tests included the addition of 0.3% NaCl. Slow heat-stir treatment. The C. W. Brabender Visco-AmyloGraph was used to study consistency (or relative viscosity) changes of thixotropism, gelation and texturization that occur during slow heat-stir (45 min to raise the temperature from 25°C to 92.5°C) processing of aqueous cottonseed protein suspensions (4% to 30% by weight of cottonseed products). The viscograph has a rotating sample cup that contains s t i r r i n g pins surrounded by heating elements. The cup is sealed with a l i d that contains a second set of pins surrounded with cooling elements. Both sets of pins are sensitive to changes in the consistency of the aqueous protein suspension in the cup which are graphically recorded for easy conversion to centipoise (cps) units. The mechanical thermoregulator, operating in conjunction with the heating and cooling system, permits the sample to be heated and cooled through a programmed temperature-time cycle, and sample consistency is recorded continuously. From the chart, the peak or highest consistency (relative viscosity) during the heating cycle, the apparent viscosity at any temperature during the heating or cooling cycle, the viscosity s t a b i l i t y of the hot sample and the degree of setback on cooling can be determined. The cup, containing 460 g of aqueous protein suspension and rotating at a rate of 70 rpm, was 1) maintained for 3 min at 25°C


Cherry; Food Protein Deterioration ACS Symposium Series; American Chemical Society: Washington, DC, 1982. 8

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184

FOOD PROTEIN DETERIORATION

Addition of 1% or more of NSP-isolate to a 12% SP-isolate suspension at pH 5·5 hindered the texturing process (Figure 16). Non-storage proteins or any number of non-protein constituents in these products could be interferring with the texturization mechanism of the SP-isolate. Figure 17 shows a comparison of the consistency changes during slow heat-stir treatment of 18% suspensions of SP-isolate without and with added 1% NSP-isolate to those occurring i n suspensions of the HgO-HzO-concentrate and the a i r - c l a s s i f i e d fine concentrate at pH 5.5. The H2Q-H2Û-concentrate was r e l a t i v e l y free of NSP. It contained mainly protein bodies with SP and any carbohydrate moitiés not extracted with water. The a i r - c l a s s i f i e d fraction contained maninly NSP, protein bodies with their SP contents and carbohydrates, and yielded a dual-phase system of a l i q u i d and beads of agglomerated protein bodies upon treatment. However, the H2Û-H2Û-concentrate increased in consistency during the cooling period. The final pudding-like consistency may have been due to structural changes in SP content and especially i n the fibrous and pectinaceous components under conditions of the slow heat-stir treatment. On the other hand, the changes in the l a t t e r ' s consistency may be the result of the slow heating rate that permitted some protei η denaturation before heat-setting of protei ns into the fibrous networks of the final product. Consistency Changes During Rapid Heat-Stir Processing Twenty percent SP-isolate and 16% CI suspensions at various pHs of 3.0 to 10.0 were subjected to a rapid heat-stir (20 min to raise the temperature of a s t i r r i n g protein suspension from 25°C to 95-98°C) to determine t h e i r t e x t u r a b i l i t y by a method other than that used with the C. W. Brabender Visco-Amylo-Graph (see Experimental Procedures). Table II compares the results of these experiments. Texturization of SP-isolate by the viscograph method only occurred in suspensions at pH's 5.0, 5.5 and 8.5. The rapid heat-stir method produced texturized products in a l l suspensions at pH's 5.0 to 9.0, and gelled products at pH's 3.0, 4.0 and 10.0. Gels made at pH's 3 and 10 were dark colored and translucent. At pH 4.0, they were light cream-colored and opaque. The gels were self-sustaining, i . e . , they maintained t h e i r shape at room temperatures. No gelled products were produced with the slow heat-stir process. The rapid heat-stir method converted pH 3.0, 4.0 and 10.0 suspensions of CI to gelled products. Like the suspensions of the slow heat-stir process, those at the other pH values became only s l i g h t l y thickened pourable suspensions. Addition of 0.3% NaCl to the CI suspensions caused those at pHs between 4.0 and 9.0 to texturize during the rapid heat-stir process. Possibly, the salt reduced the s o l u b i l i t y of NSP or another component(s) and thus reduced interference with the texturization properties of SP. Figure 18 shows the textural



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1/ The panelists used a scale of 1 to 4 to score meat loaves. Taste panel evaluations subjected to one-way analysis of variance and ranking of means. Mean values having a common l e t t e r are not s i g n i f i c a n t l y different (P>0.05). £/ Standard al1-meat loaf assigned an arbitrary value of 4.0.

Aroma I n i t i a l flavor General flavor Aftertaste Juiciness Chewiness Color Texture Moisture Overall quality

Quality Attributes

Table V I . Sensory evaluation!/ of cooked meat loaves containing various amounts of textured SP-isolate (23)



196


meat loaf in aftertaste, color, texture and moisture. None of the meat loaves containing texturized SP-isolate had aroma, j u i c i n e s s , and overal1 quality as good as the reference loaf. Meat loaves containing 30% texturized SP-isolate and added o i l , with or without added flavor, scored higher on general flavor characteristics than the 30% SP-isolate-meat loaf (Table V I I ) . Meat loaves prepared with 30% texturized CI plus o i l , or o i l and added flavoring, were scored higher in i n i t i a l f l a v o r , j u i c i ness and moisture than the 30% texturized CI-meat loaves without the o i l and flavor. However, quality attributes of these products were not as good as those of the all-meat loaf (Table VIII). In general, meat loaves formulated with heavy beef and added beef flavor and l i p i d to replace those properties lost due to the substitution of meat with the bland, fat-free, texturized SP-isolate and CI should become more acceptable with higher levels of texturized cottonseed proteins. Conclusions Increasing the temperature of a constantly s t i r r i n g aqueous suspension of cottonseed SP-isolate from 25°C to 95-98°C i n 20 min (rapid heat-stir method), or to 92.5°C in 45 min (slow heats t i r method) produced texturized products with mouth-feel and chewiness similar to cooked chopped meat. The texturized products were comparable to those formed by the spinning and thermoplastic extrusion processes. The cottonseed C I , which contains both NSP and SP, requires suspension in a 0.3% NaCl solution before i t texturizes. Formation of the textured products was pH-related, occurring mainly when the suspensions were between pH's 5.0 and 9.0. At the other pH values, suspensions form heat-stable, self-sustaining, g e l a t i n - l i k e products or thickened pourable suspensions. The suspensions should contain 7% or more protein isolate to obtain quality textured products or gels. Texturization of SP-isolate and CI provides products demonstrating 160% and 250% weight increases, respectively. Addition of 1% soluble starch produces similar results as 0.3% NaCl, in that i t enhances the t e x t u r a b i l i t y of the protein isolates. Cottonseed flour undergoes texturization in the presence of 0.3% NaCl by the rapid heat-stir method after i t s protei ns have been preheattreated at 60°C for 30 min and cooled. The texturization is improved after the f l o u r ' s protei ns have been modified by succinic or acetic anhydride. Although the degree of texturing of these treated flours was not similar to the optimum textura b i l i t y of the SP-isolate and C I , the likelihood exists for improving their functionality by further protein modification(s). The texturized proteins can be dehydrated to provide stable storage products and rehydrated to t h e i r original form when needed to formulate fabricated meat-like foods and feeds.



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! / The panelists used a scale of 1 to 4 to score meat loaves. Taste panel results subjected to one-way analysis of variance and ranking order of means. Mean values having a common l e t t e r are not s i g n i f i cantly different (P>0.05). tJ Std Ref = standard reference all-meat loaf assigned arbitrary value

Aroma I n i t i a l flavor General flavor Aftertaste Juiciness Chewiness Color Texture Moisture Overall quality

Quality Attribute

Table V I I . Sensory evaluation!/ of cooked meat loaves containing 30% textured SP-isolate and with or without added o i l and flavor (23)




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Texturization and Gelation - American Chemical Society

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