Protein Functionality in Foods - American Chemical Society

9 Water and Fat Absorption C. W. HUTTON

Department of Food, Nutrition, and Institution Management, The University of Alabama, University, AL 35486

Downloaded by CORNELL UNIV on June 4, 2017 | http://pubs.acs.org Publication Date: March 6, 1981 | doi: 10.1021/bk-1981-0147.ch009

A. M. CAMPBELL Agricultural Experiment Station and College of Home Economics, The University of Tennessee, Knoxville, TN 37916 This chapter does not purport to be the final word on water and fat absorption of plant proteins. Rather, it is designed to summarize information on the mechanism of protein interaction with water and fat, to pull together the various terms used to describe and methods used to assess water and fat absorption, and to encourage a more uniform and quantitative approach to the study of protein functionality and performance in food. The major protein products to be examined in this review are of soy origin; other products will be reviewed briefly in comparisons with soy products. Protein is utilized in many foods for the particular characteristics that it contributes to the final product (1). In order for protein products to maintain or enhance the quality and acceptability of a food, the protein ingredients should possess certain functional properties that are compatible with the other ingredients and environmental conditions of the food system (2). Consequently, an important aspect o f the development o f new prot e i n a d d i t i v e s and t h e i r i n c o r p o r a t i o n i n t o food systems i s the establishment o f t h e i r f u n c t i o n a l p r o p e r t i e s . F u n c t i o n a l prope r t i e s o f p r o t e i n s are physicochemical p r o p e r t i e s through which they c o n t r i b u t e t o the c h a r a c t e r i s t i c s o f food. Study o f funct i o n a l i t y should provide i n f o r m a t i o n as t o how a p r o t e i n a d d i t i v e w i l l perform i n a food system (2, _3, 4 ) . These p r o p e r t i e s are a f f e c t e d by p r o t e i n source, composition, and s t r u c t u r e ; p r i o r treatment; and i n t e r a c t i o n with the p h y s i c a l and chemical environment. I t i s g e n e r a l l y b e l i e v e d that p r o t e i n s are the p r i n c i p a l f u n c t i o n a l component of p l a n t a d d i t i v e s . However, i n products such as f l o u r s and meals, the carbohydrates a l s o may p l a y an a c t i v e r o l e i n the f u n c t i o n a l performance o f the a d d i t i v e s . Water absorption o r h y d r a t i o n i s considered by some as the f i r s t and the c r i t i c a l step i n imparting d e s i r e d f u n c t i o n a l prope r t i e s t o p r o t e i n s . Most a d d i t i v e s are i n dehydrated form; the i n t e r a c t i o n w i t h water i s important t o p r o p e r t i e s such as hydrat i o n , s w e l l i n g , s o l u b i l i t y , v i s c o s i t y , and g e l a t i o n . P r o t e i n has been reported t o be p r i m a r i l y r e s p o n s i b l e f o r water a b s o r p t i o n , 0097-6156/81/0147-0177$06.00/0 © 1981 American Chemical Society

Cherry; Protein Functionality in Foods ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


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although other c o n s t i t u e n t s o f the a d d i t i v e have an e f f e c t . Primary protein-water i n t e r a c t i o n s occur at p o l a r amino a c i d s i t e s on the p r o t e i n molecules. Water r e t e n t i o n of p r o t e i n s i s r e l a t e d to the p o l a r groups, such as c a r b o n y l , h y d r o x y l , amino, c a r b o x y l , and s u l f h y d r y l groups; most p r o t e i n s c o n t a i n numerous p o l a r s i d e chains along t h e i r peptide backbone, making them h y d r o p h i l i c . Water b i n d i n g v a r i e s w i t h the number and type of p o l a r groups (5). Other f a c t o r s that a f f e c t the mechanism of protein-water i n t e r a c t i o n s i n c l u d e p r o t e i n conformation and environmental f a c t o r s that a f f e c t p r o t e i n p o l a r i t y and/or conformation. Conformational changes i n the p r o t e i n molecules can a f f e c t the nature and a v a i l a b i l i t y of the h y d r a t i o n s i t e s . T r a n s i t i o n from g l o b u l a r to random c o i l conformation may expose p r e v i o u s l y b u r i e d amino a c i d s i d e c h a i n s , thereby making them a v a i l a b l e t o i n t e r a c t w i t h aqueous medium. Consequently, an unfolded conformation may permit the p r o t e i n to bind more water than was p o s s i b l e i n the g l o b u l a r form ( 6 ) . Fat absorption of p r o t e i n a d d i t i v e s has been s t u d i e d l e s s e x t e n s i v e l y than water absorption and consequently the a v a i l a b l e data are meager. Although the mechanism of f a t absorption has not been e x p l a i n e d , f a t absorption i s a t t r i b u t e d mainly to the p h y s i c a l entrapment of o i l ( 7 ) . Factors a f f e c t i n g the p r o t e i n l i p i d i n t e r a c t i o n i n c l u d e p r o t e i n conformation, p r o t e i n - p r o t e i n i n t e r a c t i o n s , and the s p a t i a l arrangement of the l i p i d phase r e s u l t i n g from the l i p i d - l i p i d i n t e r a c t i o n . Non-covalent bonds, such as hydrophobic, e l e c t r o s t a t i c , and hydrogen, are the f o r c e s i n v o l v e d i n p r o t e i n - l i p i d i n t e r a c t i o n s ; no s i n g l e molecular f o r c e can be a t t r i b u t e d t o p r o t e i n - l i p i d i n t e r a c t i o n s ( 8 ) . Experimental

Procedures

Water Absorption Various terms and methods have been proposed i n the l i t e r a t u r e to d e s c r i b e and evaluate the uptake of water by a p r o t e i n i n g r e d i e n t . U n f o r t u n a t e l y , few s t a n d a r d i z e d methods e x i s t f o r the e v a l u a t i o n of t h i s f u n c t i o n a l p r o p e r t y ; most methods have developed piecemeal and are e m p i r i c a l . To d e s c r i b e the uptake of water, water a b s o r p t i o n , water b i n d i n g , water h y d r a t i o n c a p a c i t y , water h o l d i n g , s w e l l i n g , and p o s s i b l y other terms have been used. Frequently, the terminology i s r e l a t e d to the method employed (9). These terms o f t e n are misleading and confusing i n the i n t e r p r e t a t i o n of r e s u l t s . Consequently, some of the p u b l i s h e d data are o f l i m i t e d use. C u r r e n t l y , the methods f o r e v a l u a t i n g the uptake of water appear to have been narrowed to f o u r as f o l l o w s : 1} R e l a t i v e humidity method. Water absorption i s defined as the water absorbed by a d r i e d p r o t e i n powder w i t h e q u i l i b r a t i o n against water vapor at a known r e l a t i v e humidity. This method, a l s o known as the e q u i l i b r i u m moisture content (EMC) method, was described f i r s t by Mellon et a l . (10). Huffman et a l . (11) used



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the EMC method f o r measuring moisture absorption and r e t e n t i o n of f i v e v a r i e t i e s of sunflower meal. As seen i n Figure 1, l i t t l e d i f f e r e n c e was noted i n water absorption over a wide range of r e l a t i v e humidity (RH); the approximate was only 10-17% at RH up to 70%. At higher RH, EMC rose r a p i d l y to more than 30% at 90% RH. V a r i e t a l d i f f e r e n c e s were reported to a f f e c t EMC, and t h i s was a t t r i b u t e d to d i f f e r e n c e s i n carbohydrate content. Yet, prot e i n content was h i g h l y c o r r e l a t e d with water absorption. Hagenmaier (12) reported that p r o t e i n s may be ranked i n order of water binding c a p a c i t y at one r e l a t i v e humidity and that t h i s order should hold t r u e at other r e l a t i v e h u m i d i t i e s . He evaluated water b i n d i n g of s e v e r a l o i l s e e d p r o t e i n s at 84% RH; water b i n d i n g increased as the number of h y d r o p h i l i c groups of the d i f f e r e n t p r o t e i n s increased. 2) S w e l l i n g method. Measurement of s w e l l i n g i s a second method used t o estimate water absorption of a sample. A s w e l l i n g apparatus was devised and described by Hermansson (2, 13). In t h i s method, a small amount of sample i s dusted on a wet f i l t e r paper fastened on a g l a s s f i l t e r . The f i l t e r i s f i t t e d on top o f a thermostated funnel f i l l e d with water and connected to a h o r i z o n t a l l y l o c a t e d c a p i l l a r y . The uptake of f l u i d i s f o l l o w e d i n the c a p i l l a r y ; evaporative losses are prevented by a g l a s s l i d (2). S w e l l i n g i s defined as the spontaneous uptake of water by tKe a d d i t i v e . Most m a t e r i a l s of i n t e r e s t as i n g r e d i e n t s are n e i t h e r comp l e t e l y s o l u b l e nor completely i n s o l u b l e , and most foods are water swollen systems. The concept of uptake of water or s w e l l ing may, t h e r e f o r e , provide v a l u a b l e i n f o r m a t i o n f o r e v a l u a t i o n of a p r o t e i n as a food i n g r e d i e n t . S w e l l i n g was defined by Hermansson (2) as . . . the spontaneous uptake of a s o l v e n t by a s o l i d . I t i s a phenomenon f r e q u e n t l y observed as the f i r s t step i n the s o l v a t i o n of polymers, i n which case s w e l l i n g continues u n t i l the molecules are randomized w i t h i n the system. In other cases s o l v a t i o n may be prevented by v a r i o u s i n t e r m o l e c u l a r forces i n the swollen sample, r e s u l t i n g i n l i m i t e d s w e l l i n g and a d e f i n i t e volume i n c r e a s e . Hermansson and co-workers {2_ 1^5, 14) examined the s w e l l i n g a b i l i t y of a soybean p r o t e i n i s o l a t e (P-D), sodium c a s e i n a t e , whey p r o t e i n concentrate (WPC) and f i s h p r o t e i n concentrate (FPC) i n pure water and as i n f l u e n c e d by pH and i o n i c s t r e n g t h . The s w e l l i n g c h a r a c t e r i s t i c s of the v a r i o u s p r o t e i n s were e n t i r e l y d i f f e r e n t . The d i f f e r e n c e s i n c l u d e d magnitude o f s w e l l i n g , the time t o reach maximum s w e l l i n g , the tendency to s o l u b i l i z e , and the response to the chemical environment. G e n e r a l l y , P-D exhibi t e d very good s w e l l i n g , which was considered to be a l i m i t e d type o f s w e l l i n g . Caseinate a l s o showed a high degree of 9



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Figure 1. Water absorption of sunflower meals. Sunflower varieties: (A) Arrowhead; (%) Mingren; (A) Greystripe; (O) Peredovik; (^) Krasnodarets (11).

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s w e l l i n g , which was o f the u n l i m i t e d type; that i s , s w e l l i n g was high p r i o r t o s o l v a t i o n . The WPC and FPC showed poor s w e l l i n g a b i l i t y . Hermansson (2) contends that s w e l l i n g , together w i t h s o l u b i l i t y d a t a , could~l>e a u s e f u l guide t o f u n c t i o n a l i t y . A m o d i f i c a t i o n o f the s w e l l i n g apparatus was used to evaluate WPC, peanut p r o t e i n , s i n g l e c e l l p r o t e i n (SCP), and chicken preen gland p r o t e i n . Chicken p r o t e i n e x h i b i t e d the h i g h e s t s w e l l i n g values f o l l o w e d i n decreasing order by peanut, SCP, and WPC products (15). Problems a s s o c i a t e d w i t h use o f t h i s method i n v o l v e product i o n o f the apparatus and lack o f r e p r o d u c i b i l i t y o f the t e s t c o n d i t i o n s , s p e c i f i c a l l y , a p p l i c a t i o n o f samples i n r e p r o d u c i b l e thickness t o the wet f i l t e r paper (16). 3) Excess water method. A t h i r d method, which r e p o r t e d l y measures b i n d i n g , i n v o l v e s exposure o f the sample t o excess water and a p p l i c a t i o n o f m i l d f o r c e ( u s u a l l y c e n t r i f u g a l ) t o separate the r e t a i n e d o r "bound" water from the f r e e water. The amount of water r e t a i n e d , u s u a l l y determined as the weight g a i n , i s reported as water absorption expressed as a percentage o f the dry sample weight. This method, t o date, has been used most frequentl y by researchers (17, 18, 19, 20). The d e t a i l s o f the s p e c i f i c procedures v a r y , as do the u n i t s o f expressing water a b s o r p t i o n . Other drawbacks are that t h i s method, unless considerably modif i e d , does not account f o r the p r o t e i n and carbohydrate s o l u b i l i z e d by the procedure o r f o r the low-density components t h a t f l o a t on the supernatant s u r f a c e . For these reasons, some r e searchers (16) suggest t h a t the excess water method i s s u i t able only f o r use on p r o t e i n a d d i t i v e s that a r e mainly i n s o l u b l e . For measuring water absorption by the excess water method, the techniques developed by J a n i c k i and Walczak (described by Hamm, 21) f o r meats and by S o s u l s k i (22) f o r wheat f l o u r are modif i e d . L i n e t a l . (17) m o d i f i e d the S o s u l s k i technique f o r use w i t h sunflower and soy meal products. T h i s m o d i f i e d procedure has been employed f o r much o f the research on water a b s o r p t i o n o f p l a n t p r o t e i n a d d i t i v e s . Water absorption c a p a c i t i e s o f a soy f l o u r , two soy concentrates, and two soy i s o l a t e s were compared by L i n e t a l . (17) t o those o f a sunflower f l o u r , three sunflower concentrates, and one sunflower i s o l a t e . The percent water abs o r p t i o n o f the soy products increased as the t o t a l p r o t e i n content o f the samples increased from f l o u r t o i s o l a t e . The soy f l o u r absorbed 130% water, the soy concentrates absorbed an average o f 212% water, and the soy i s o l a t e s absorbed an average o f 432% water. No c a l c u l a t i o n s were made, however, that r e l a t e d the percent water absorbed t o p r o t e i n content o f the samples. The sunflower p r o d u c t s , though s i m i l a r i n p r o t e i n content, d i d not respond i n the same magnitude o r d i r e c t i o n as the soy products. A l l sunflower products had lower water absorption values than d i d t h e i r soy c o u n t e r p a r t s , and water absorption d i d not p a r a l l e l p r o t e i n content. The water absorption value f o r the i s o l a t e (155%) was w i t h i n the range (138-203%) reported f o r the sunflower



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concentrates. On the b a s i s o f these d a t a , the researchers suggested t h a t the soy p r o t e i n s are more h y d r o p h i l i c than the sunflower proteins. Fleming et a l . (18), u s i n g the procedure o f J a n i c k i and Walczak, a l s o compared the water absorption c h a r a c t e r i s t i c s o f sunflower and soybean products. Water absorption o f the soy products increased as p r o t e i n content o f the samples i n c r e a s e d . C o n s i s t e n t w i t h the f i n d i n g s o f L i n et a l . (17) , water absorption of the sunflower products was below t h a t o f the soy products except f o r the concentrates, which had values s i m i l a r to those o f the soy counterpart, and the water absorptions o f the sunflower concentrates and i s o l a t e s were o f s i m i l a r magnitude. The water a b s o r p t i o n o f a l f a l f a l e a f p r o t e i n (ALP) e x t r a c t e d and prepared by d i f f e r e n t methods was compared t o t h a t o f a soy concentrate and a soy i s o l a t e (19). The method f o r determining water absorption was that o f L i n et a l . (17) and Fleming et a l . (18); u n i t s f o r water absorption were g H20/g l e a f p r o t e i n . The values reported f o r the ALP provide i n f o r m a t i o n concerning the e f f e c t o f p r o c e s s i n g on w.rter a b s o r p t i o n . Of more i n t e r e s t t o t h i s reviewer, however, i s the r e s e a r c h e r s use, as standards f o r water a b s o r p t i o n , o f two soy products, a concentrate, Promosoy100, and an i s o l a t e , Promine-D, which have been evaluated by other researchers employing the excess w a t e r / c e n t r i f u g e method. Hutton (23) and Hutton and Campbell (20) examined the e f f e c t o f pH and temperature on the water a b s o r p t i o n o f these same two soy products u s i n g a m o d i f i c a t i o n o f t h i s method. Values f o r water a b s o r p t i o n f o r these products as compiled from the v a r i o u s s t u d i e s are recorded i n Table I . The same products were used, and a s i m i l a r ( s i m i l a r only i n terms o f referenced method being excess water) procedure was used. The c o n d i t i o n s of the t e s t undoubtedly were m o d i f i e d f o r the p a r t i c u l a r l a b o r a t o r i e s or researchers o r t o be compatible w i t h other measurements or v a r i a b l e s evaluated i n the r e s p e c t i v e s t u d i e s . In summary, w i t h i n the c o n d i t i o n s o f a p a r t i c u l a r t e s t , a l l researchers r e p o r t e d , w i t h one e x c e p t i o n , a g r e a t e r water a b s o r p t i o n by the i s o l a t e than the concentrate, p o s s i b l y i n d i c a t i n g a r e l a t i o n s h i p between water absorption and p r o t e i n content. This has been suggested by s e v e r a l i n v e s t i g a t o r s . The one e x c e p t i o n , as reported by Hutton (23), was t h a t the water absorption of the concentrate was g r e a t e r than t h a t o f the i s o l a t e at pH 5.0. At pH 5.0, the i s o e l e c t r i c p o i n t (IEP) o f the p r o t e i n i s being approached. Perhaps, at the IEP, the prot e i n has l e s s o f an e f f e c t and the h y d r o p h i l i c carbohydrates have p r o p o r t i o n a t e l y more o f an e f f e c t on water a b s o r p t i o n than a t other pH l e v e l s . P o s s i b l y the r e l a t i o n s h i p between water absorpt i o n and s o l u b i l i t y , y e t t o be d i s c u s s e d , accounts i n p a r t f o r the statement by Quinn and Paton (16) that the excess water method i s s u i t a b l e f o r products t h a t are mainly i n s o l u b l e . Hutton (23) and Hutton and Campbell (20) used the excess water method i n combination w i t h the s o l u b i l i t y measurements but d i d not adjust the absorption data f o r the s o l u b i l i z e d p r o t e i n , 1



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which was q u i t e d i f f e r e n t f o r the two products. A r e c a l c u l a t i o n of these data to adjust the absorption values f o r the s o l u b i l i z e d p r o t e i n r e s u l t e d i n the comparisons o f o r i g i n a l and adjusted values shown i n Tables I I and I I I f o r a soy p r o t e i n concentrate and i s o l a t e , r e s p e c t i v e l y . S o l u b i l i z e d carbohydrate was not cons i d e r e d i n the adjusted v a l u e s . Taking the l o s s o f s o l u b l e p r o t e i n i n t o account i n c a l c u l a t ing water a b s o r p t i o n can i n f l u e n c e the conclusions drawn i n some s t u d i e s . E l g e d a i l y and Campbell (24) used the excess water method (23) i n studying the e f f e c t s o f soHTum c h l o r i d e and sucrose on the water a b s o r p t i o n o f three soy p r o t e i n i s o l a t e s . They a l s o determined n i t r o g e n s o l u b i l i t y and used the values f o r an a l t e r n a t i v e method o f c a l c u l a t i o n i n which the a b s o r p t i o n values r e f l e c t e d a c o r r e c t i o n f o r the e x t r a c t e d p r o t e i n . With both methods o f c a l c u l a t i o n i t was assumed t h a t added sodium c h l o r i d e and sucrose were e x t r a c t e d i n the determination o f s o l u b l e n i t r o gen. With tHe method o f c a l c u l a t i o n i n which the e x t r a c t e d prot e i n was d i s r e g a r d e d , the a n a l y s i s o f v a r i a n c e showed soy i s o l a t e , l e v e l o f sodium c h l o r i d e , and t h e i r i n t e r a c t i o n t o s i g n i f i c a n t l y a f f e c t water a b s o r p t i o n . When the c o r r e c t i o n was made, only the soy i s o l a t e appeared t o have a s i g n i f i c a n t e f f e c t on water absorption. In a current study i n the same l a b o r a t o r y (25), the c o r r e c t i o n i s being made by determining the t o t a l s o l i d s i n the supernatant. This approach might be p r e f e r a b l e i n a study i n which other i n g r e d i e n t s are added t o the soy products. 4) Water s a t u r a t i o n method. More r e c e n t l y , a method has been described by Quinn and Paton (16), who c l a i m t h a t t h e i r procedure more c l o s e l y simulates a c t u a l food p r o d u c t i o n a p p l i c a t i o n s than does the excess water method. In t h i s technique, only enough water, e s s e n t i a l l y a l l o f which i s r e t a i n e d upon c e n t r i fl i g a t i o n , i s added t o s a t u r a t e the sample. A comparison of the excess water method and the proposed method f o r v a r i o u s p r o t e i n products, as reported by Quinn and Paton, i s presented i n Table IV. Values f o r water a b s o r p t i o n by the Quinn and Paton method are d i f f e r e n t from values obtained i n the same l a b o r a t o r y by the excess water method, p a r t i c u l a r l y f o r the more s o l u b l e p r o t e i n m a t e r i a l s ; however, water a b s o r p t i o n values determined by the "same" method by v a r i o u s i n v e s t i g a t o r s are not always s i m i l a r e i t h e r (Table I ) . Quinn and Paton (16) observed that the i n t e n s i t y and d u r a t i o n o f mixing i n f l u e n c e d the water uptake o f the m a t e r i a l s i n v e s t i gated, and t h a t the measurement was not r e p r o d u c i b l e unless the time o f a g i t a t i o n was constant (2 min was chosen). One product, sodium c a s e i n a t e , r e q u i r e d longer than a 2-min mixing time. These i n v e s t i g a t o r s s t a t e t h a t the proposed technique measures water absorbed and r e t a i n e d under s p e c i f i c c o n d i t i o n s , which may o r may not apply t o p a r t i c u l a r manufacturing a p p l i c a t i o n s . They do, however, s t a t e that t h i s method w i t h the a p p l i c a t i o n o f l i m i t e d


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Table I . Water a b s o r p t i o n values f o r a soy concentrate and i s o l a t e as r e p o r t e d i n s e v e r a l s t u d i e s . Reference Number

Concentrate (Promosoy-100)

Isolate (Promine-D)


0. 0

17 18 l& 29 23 23 23

196 -330 340 273 241

417 775 > 415a,c 638 1218d 350 190f a

a

b

a

d

e

a

V a l u e s r e p o r t e d were converted t o percent a b s o r p t i o n . Sample mixed 1 min. Sample mixed 10 min. dpH 7.0. pH 6.0. pH 5.0b

c

e

f

Table I I . Water a b s o r p t i o n mean values determined by excess water method and as adjusted f o r s o l u b i l i z e d prot e i n f o r a soy concentrate (23). Adjusted f o r solubilized protein 5.0 6.0 7.0

Excess water method 5.0 6.0 7.0

pH

0. y

Q

Temp (°C) 4 ambient 90

a

247 241 305

268 273 306

326 340 537

251 248 320

278 281 342

a22-250C.


340 358 733

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Table I I I . Water absorption mean values determined by excess water method and as adjusted f o r s o l u b i l i z e d prot e i n f o r a soy i s o l a t e (23). Adjusted f o r solubilized protein 5.0 6.0 7.0

Excess water method 5.0 6.0 7.0

pH


%

Temp (°C) 4 ambient 90 a

a

175 190 408

457 350 493

975 1218 1158

183 204 440

492 475 703

1845 2500 4958

22-25°C.

Table IV.

Water h y d r a t i o n c a p a c i t y values o f v a r i o u s p r o t e i n m a t e r i a l s (16).

Excess water method

Proposed method"

1.05 3.10 3.50 6.70 4.50 0.00 1.30 0.00

1.31 3.00 3.85 5.50 3.29 2.33 0.67 0.97

a

Pea concentrate Promosoy-100 concentrate Promine-D i s o l a t e Supro 620 i s o l a t e Rapeseed concentrate Caseinate Egg white Whey concentrate

aMethod o f Fleming et a l . (18). W a l u e s were obtained before the technique was s t a n d a r d i z e d . The values are estimates o f where the WHC l i e s w i t h i n the e x p e r i m e n t a l l y determined range. Cereal Chemistry


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r a t h e r than excess water more c l o s e l y simulates a c t u a l food product c o n d i t i o n s . C e r t a i n drawbacks o f the method are e v i d e n t . Water absorption has been shown by Quinn and Paton and by others to be a f f e c t e d by time of exposure of product to water; the c o n t r o l l e d l i m i t e d exposure time i n t h i s method may make the values more r e p r o d u c i b l e , but does i t simulate a c t u a l performance c o n d i t i o n s ? A l s o , t h i s method e l i m i n a t e s the problem of s o l u b i l i z e d p r o t e i n ; the s o l u b i l i z e d p r o t e i n may have an important e f f e c t on water absorption by being no longer a v a i l a b l e to be hydrated.


Fat Absorption For f a t a b s o r p t i o n , the measurements have been fewer and more c o n s i s t e n t than those reported f o r water a b s o r p t i o n . Theref o r e , one should be able to examine w i t h more s e c u r i t y the data of separate s t u d i e s . The main problem a s s o c i a t e d w i t h the f a t absorption method appears to be that r a r e l y , i f ever, i s a food system encountered that i n v o l v e s only the p r o t e i n - l i p i d interaction. Fat absorption of p r o t e i n a d d i t i v e s u s u a l l y i s measured by adding excess l i q u i d o i l to a p r o t e i n powder, mixing and h o l d i n g , c e n t r i f u g i n g , and determining the amount of absorbed o i l ( t o t a l minus f r e e ) (17, 26). The amount o f o i l and sample, k i n d o f o i l , h o l d i n g and c e n t r i f u g i n g c o n d i t i o n s , and u n i t s of expression have v a r i e d s l i g h t l y from one i n v e s t i g a t o r to another; consequently, f a t a b s o r p t i o n values f o r the same products have v a r i e d among i n v e s t i g a t o r s . Values f o r Promosoy-100 and Promine-D, as reported i n three separate s t u d i e s , which were most c o n s i s t e n t i n methodology, are reported i n Table V. V a r i a t i o n s do e x i s t i n the v a r i o u s s t u d i e s to be reviewed, f a t a b s o r p t i o n o f p r o t e i n s i s a f f e c t e d by p r o t e i n source, extent of p r o c e s s i n g and/or composit i o n of a d d i t i v e , p a r t i c l e s i z e , and temperature. Water Absorption Response Patterns Considering the l i m i t a t i o n s presented thus f a r that are inherent i n i n t e r p r e t i n g data reported i n the l i t e r a t u r e , perhaps the p a t t e r n o f response r a t h e r than the i n d i v i d u a l measurements i s of importance i n p r e d i c t i n g f u n c t i o n a l i t y . Information w i l l be presented t h a t r e l a t e s water a b s o r p t i o n to other f u n c t i o n a l p r o p e r t i e s and examines the e f f e c t o f the p h y s i c a l and chemical environment on the water absorption response p a t t e r n s of v a r i o u s p r o t e i n i n g r e d i e n t s . This p r e s e n t a t i o n w i l l be b r i e f and w i t h l i m i t e d e x p l a n a t i o n . O r i g i n a l references may be consulted by those d e s i r i n g g r e a t e r depth. R e l a t i o n s h i p s w i t h other p r o p e r t i e s . In any food system and p o s s i b l y i n simple systems, the p r o t e i n i n g r e d i e n t i s l i k e l y to perform s e v e r a l f u n c t i o n s , most of which are being discussed i n



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d e t a i l i n d i v i d u a l l y i n t h i s book. Since water b i n d i n g or absorpt i o n may be a r e s u l t of other p r o p e r t i e s , i t seems of i n t e r e s t to mention some r e l a t i o n s h i p s . Hermansson (27) s t a t e s t h a t "waterb i n d i n g may be caused by any of the f o l l o w i n g p r o p e r t i e s : (a) the a b i l i t y to s w e l l and take up water; (b) a high v i s c o s i t y caused by s o l u b l e molecules, swelled p a r t i c l e s or a mixture; (c) the a b i l i t y to form a g e l network during p r o c e s s i n g . " Inherent i n t h i s explanation o f water b i n d i n g are the a s s o c i a t i o n s of the absolute water absorption ( p r e v i o u s l y d i s c u s s e d ) , s o l u b i l i t y , v i s c o s i t y , and g e l a t i o n f u n c t i o n s . In Table V I , data are presented t h a t demonstrate the e f f e c t o f temperature on the s o l u b i l i t y , s w e l l i n g , and v i s c o s i t y p r o p e r t i e s of a soy i s o l a t e . S o l u b i l i t y : The reported r e l a t i o n s h i p between water absorption and s o l u b i l i t y of p r o t e i n s has not been c o n s i s t e n t . Water absorption c a p a c i t y of sunflower concentrates increased s l i g h t l y as the s o l u b i l i t y index of the p r o t e i n decreased (17). Hermansson (2) reported t h a t a h i g h l y s o l u b l e p r o t e i n e x h i b i t s poor water b i n d i n g , but a reverse r e l a t i o n s h i p between water a b s o r p t i o n , evidenced by s w e l l i n g and s o l u b i l i t y , was not observed. In a l a t e r r e p o r t , Hermansson (27) s t a t e d t h a t s o l u b i l i t y measurements give no i n f o r m a t i o n as to whether or not a p r o t e i n w i l l b i n d water. Hagenmaier (10) demonstrated t h a t pH had l i t t l e e f f e c t on water absorption of o i l s e e d p r o t e i n products, but s o l u b i l i t y was pH dependent. He suggested that the d i f f e r i n g degree of dependence on pH i n d i c a t e s t h a t water absorption and p r o t e i n s o l u b i l i t y are not c o r r e l a t e d . C o n t r a s t i n g l y , Wolf and Cowan (28) reported the pH-water r e t e n t i o n curve of soy p r o t e i n s t o f o l l o w the p H - s o l u b i l i t y curve. Both s o l u b i l i t y and water r e t e n t i o n were minimal at the i s o e l e c t r i c p o i n t (4.5) and increased as the pH diverged from t h i s p o i n t . Hutton and Campbell (20) reported that the e f f e c t s of pH and temperature on water absorption o f soy products p a r a l l e l e d those of s o l u b i l i t y f o r the most p a r t . At pH 7.0, as temperature increased from 4 t o 90°C, s o l u b i l i t y increased but water absorption increased then decreased. This suggested that water absorption and s o l u b i l i t y may be r e l a t e d t o a p o i n t , perhaps maximum h y d r a t i o n , at which s o l u b i l i t y continues to increase and h y d r a t i o n does not. This appears c o n s i s t e n t w i t h the statements of Hermansson (2) t h a t water a b s o r p t i o n i s the f i r s t step i n the s o l v a t i o n of polymers, and s w e l l i n g may be l i m i t e d or u n l i m i t e d . V i s c o s i t y and g e l a t i o n : Many p r o t e i n s absorb water and s w e l l , causing changes that are r e f l e c t e d by concurrent increases i n v i s c o s i t y (9). V i s c o s i t y has been reported to be i n f l u e n c e d by s o l u b i l i t y and s w e l l i n g (2_, 19) . As water absorption (determined as s w e l l i n g ) i n c r e a s e d , v i s c o s i t y a l s o increased (2). Fleming et a l . (18) reported t h a t water absorpt i o n was a t t r i b u t a b l e to the p r o t e i n content o f the product and t h a t v i s c o s i t y increased e x p o n e n t i a l l y as p r o t e i n content i n c r e a s e d , thereby suggesting a p o s s i b l e r e l a t i o n s h i p between


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Fat a b s o r p t i o n values f o r a soy concentrate and i s o l a t e as r e p o r t e d i n s e v e r a l s t u d i e s .

Reference Number

Concentrate

17 19 23 a

FUNCTIONALITY

92 101* 74

Isolate

119 156 121

a

Reported values were converted from ml o i l / g t o % by m u l t i p l y i n g by s p e c i f i c g r a v i t y o f o i l and m u l t i p l y i n g by 100.

Table V I . E f f e c t o f temperature on some f u n c t i o n a l of soy i s o l a t e ( 7 ) .

properties

a

Temperature (°C) 25 70 80 90 100

Solubility (%)

Swelling (ml/g)

Viscosity 15S-

53 67 68 71 81

10 17 20 17 14

3620 7490 5280 1410

1

a

Measurements were made at 25°C a f t e r heat treatment. Journal of the American Oil Chemists' Society


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water absorption and v i s c o s i t y . Hutton (23) reported that above pH 5.0, the water absorption of soy i s o l a t e s was greater than that of soy concentrates, and that v i s c o s i t y was g r e a t e r f o r the i s o l a t e than the concentrate. However, pH and temperature v a r i a t i o n s brought about d i f f e r e n t responses i n water a b s o r p t i o n and v i s c o s i t y between the concentrate and i s o l a t e . This suggests t h a t water absorption and v i s c o s i t y are not always c o r r e l a t e d , at l e a s t i n products of q u i t e d i f f e r e n t proximate composition. A g e l can be considered as a s t r u c t u r a l m a t r i x h o l d i n g l i q u i d and can be formed spontaneously by s w e l l i n g at high prot e i n concentrations (7, 27). Yet no s t u d i e s have been reviewed that r e l a t e d water absorption and g e l a t i o n . The g e l a t i o n phenomenon of soybean p r o t e i n s has been s t u d i e d i n d e t a i l by Catsimpoolas and Meyer (29, 30, 31). Environment. The p h y s i c a l and chemical environments have been shown t o a f f e c t the f u n c t i o n a l performance o f p r o t e i n s . F a c t o r s , such as c o n c e n t r a t i o n , pH, temperature, i o n i c s t r e n g t h , and presence o f other components, a f f e c t the balance between the f o r c e s u n d e r l y i n g p r o t e i n - p r o t e i n and p r o t e i n - s o l v e n t i n t e r a c t i o n s (9). Most f u n c t i o n a l p r o p e r t i e s are determined by the balance between these f o r c e s . Although the comparison o f d i s c r e t e data from v a r i o u s s t u d i e s might be o f l i m i t e d v a l u e , c o n s i d e r a t i o n of the response p a t t e r n s of p r o t e i n a d d i t i v e s to changes i n the environment of simple and/or food systems might be fruitful. For products of d i s s i m i l a r composition, e.g., i s o l a t e s , conc e n t r a t e s , and f l o u r s , changes i n the chemical environment undoubtedly e l i c i t d i f f e r e n t responses from the v a r i o u s cons t i t u e n t s of an i n g r e d i e n t , i . e . , p r o t e i n , carbohydrate, e t c . Perhaps the p r o p e r t i e s o f the p r o t e i n can best be examined i n the i s o l a t e because o f i t s r e l a t i v e l y low c o n c e n t r a t i o n of nonprotein c o n s t i t u e n t s . U n f o r t u n a t e l y , i s o l a t e s u s u a l l y have been subjected to the most extensive p r o c e s s i n g , which a l s o a f f e c t s the response of the p r o t e i n . Concentration: G e n e r a l l y , as product c o n c e n t r a t i o n i n c r e a s e s , water absorption i n c r e a s e s . Much controversy e x i s t s concerning what a c t u a l l y i s being measured i n w a t e r - u n l i m i t e d and w a t e r - l i m i t e d systems. Obviously, as product c o n c e n t r a t i o n increases to the p o i n t t h a t water i s l i m i t e d , water absorption ceases to i n c r e a s e . Hansen (32) reported t h a t as p r o t e i n content increased from 32 to 90%, water absorption o f the soy samples i n c r e a s e d . This can be seen i n Figure 2. Although the trend i s e v i d e n t , the i n c r e a s e was not l i n e a r , which suggests t h a t f a c t o r s i n a d d i t i o n to p r o t e i n were c o n t r i b u t i n g to water a b s o r p t i o n . ( P a r t i c l e s i z e d i d not a f f e c t absorption.) As p r o t e i n content increased from soy f l o u r to soy i s o l a t e , water absorption a l s o increased. T h i s was not the case f o r sunflower products (17).



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pH: S t r u c t u r a l l y , i o n i z e d amino a c i d groups b i n d more water than nonionized groups. V a r i a t i o n i n pH a f f e c t the i o n i z a t i o n o f amino a c i d groups. Since amino a c i d composition and arrangement vary w i t h p r o t e i n o r i g i n , the response t o pH a l s o v a r i e s ( 6 ) . Hagenmaier (12) reported t h a t pH changes from 4.5 t o 7.0 had l i t t l e e f f e c t on cottonseed, soybean, and c a s e i n p r o t e i n samples. The e f f e c t , though s l i g h t , was increased water b i n d i n g as pH i n c r e a s e d ; the d i f f e r e n c e s among the samples were g r e a t e r than the change w i t h pH. S i m i l a r l y , Hermansson (14) demonstrated that s w e l l i n g o f a soy i s o l a t e , c a s e i n a t e , and WPC increased as pH i n c r e a s e d from 4.0 t o 10.0. The increase was more dramatic f o r caseinate than e i t h e r the i s o l a t e o r WPC. Wolf and Cowan (28) reported t h a t water a b s o r p t i o n o f soy p r o t e i n s was minimal a t the i s o e l e c t r i c p o i n t (4.5) and increased as the pH diverged from this point. The e f f e c t s o f pH on water a b s o r p t i o n o f a soy i s o l a t e and soy concentrate are represented i n Table V I I . Water a b s o r p t i o n of a soy i s o l a t e increased as pH increased from 5.0 t o 7.0. This i n c r e a s e was evident at a l l temperatures s t u d i e d (4°C, ambient, and 90°C). For soy concentrate samples, the e f f e c t o f pH was s i m i l a r i n d i r e c t i o n t o the e f f e c t on water absorption o f the i s o l a t e but was o f s m a l l e r magnitude (23). Fleming et a l . (18) d i d not examine the e f f e c t o f pH on water a b s o r p t i o n , but these researchers examined the e f f e c t o f "pH a c t i v a t i o n ' on water absorption o f sunflower and soy products. For pH a c t i v a t i o n , 1.25 N NaOH was added t o s l u r r i e s t o achieve pH 12.2 and then 6.0 N HC1 was added t o r e t u r n t o pH 6.0 i n 10 min. The pH a c t i v a t i o n process improved the water absorption p r o p e r t i e s f o r most products but d i d not increase water absorption of t h e soy f l o u r . Processes s i m i l a r t o pH a c t i v a t i o n may be encountered i n the p r o c e s s i n g o f vegetable p r o t e i n a d d i t i v e s . Temperature: P r o t e i n s u s u a l l y bind l e s s water at high temperatures than a t low temperatures, but i f p r o t e i n conformation changes w i t h h e a t i n g , i t could o v e r r i d e the e f f e c t o f temperature on water a b s o r p t i o n . Heating, c o n c e n t r a t i n g , d r y i n g , and t e x t u r i z i n g may a l l cause denaturation and aggregation o f p r o t e i n molecules, which may reduce the surface area and a v a i l a b i l i t y o f p o l a r amino a c i d groups f o r water b i n d i n g . P r o t e i n aggregation, i n some cases, may change the conformation i n such a way as t o increase b i n d i n g . A l l p r o t e i n a d d i t i v e s are subjected to denaturation t o some extent; t h e r e f o r e , response o f products to temperature w i l l be a f f e c t e d by product o r i g i n and p r i o r p r o c e s s i n g treatment ( 6 ) . Hermansson reported t h a t heating o f a soy i s o l a t e enhanced s w e l l i n g . Huffman e t a l . (11) reported t h a t temperature had no n o t i c e a b l e e f f e c t on water a F s o r p t i o n o f sunflower products. Hutton and Campbell (20) reported t h a t the o v e r a l l e f f e c t of temperature, d i s r e g a r d i n g pH, was increased water absorption f o r a soy i s o l a t e and a trend i n that d i r e c t i o n f o r a concentrate. The e f f e c t o f temperature on water absorption o f the soy i s o l a t e 1



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Figure 2. Water binding (grams of unfrozen water/gram of solids) by soy protein preparations, each containing 1 g of water/g of solids, as a function of protein content, where % protein (on a solids basis) = % N X 6.25: (O) soy protein isolate B; (%) soy protein concentrate; (A) soy flour (defatted); (Q) carbohydrateenriched fraction of soy concentrate (32).

-

1400

t— a.

< E

39

*0* Journal of Food Science

Figure 3.

Water absorption response surface for Promine-D with variations in pH and temperature (20)



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was l e s s than t h a t of pH and was pH dependent. This can best be viewed i n the response s u r f a c e , Figure 3. At pH 5.0, water a b s o r p t i o n increased as temperature i n c r e a s e d . At pH 6.0, water absorption decreased, then increased w i t h i n c r e a s i n g temperature. At pH 7.0, water absorption i n c r e a s e d then decreased with i n c r e a s i n g temperature. The response surface f o r the concentrate i s shown i n Figure 4 (20). For the soy concentrate, the e f f e c t of temperature was l e s s than that of pH, and water absorption increased as temperature increased from 4 to 90°C. I o n i c s t r e n g t h : S a l t s compete w i t h water f o r the b i n d i n g s i t e s on amino a c i d s i d e groups; the amount of water bound to a p r o t e i n i s a f u n c t i o n of s a l t c o n c e n t r a t i o n (6). The e f f e c t o f i o n i c s t r e n g t h on p r o t e i n f u n c t i o n a l i t y has been focused p r i m a r i l y on i t s e f f e c t on s o l u b i l i t y ( 2 ) . G e n e r a l l y , p r o t e i n s o l u b i l i t y increases at low s a l t concentrations and decreases at high s a l t c o n c e n t r a t i o n s . Hermansson (2) examined the e f f e c t o f i o n i c s t r e n g t h on s w e l l i n g o f soy i s o l a t e , c a s e i n a t e , and WPC products. The e f f e c t of NaCl on water absorption was not c o n s i s t e n t among the products. G e n e r a l l y , as i o n i c s t r e n g t h increased from 0.0 to 1.0 M NaCl, water a b s o r p t i o n increased f o r the soy i s o l a t e and c a s e i n a t e . Water absorption of WPC was l i t t l e a f f e c t e d by i o n i c s t r e n g t h . Fleming et a l . (18) examined the e f f e c t o f 5% NaCl on the water a b s o r p t i o n o f soy and sunflower f l o u r s , concentrates, and i s o l a t e s . The water absorption of the soy and sunflower f l o u r s was higher i n 5% NaCl than i n water. G e n e r a l l y , s a l t decreased water a b s o r p t i o n o f the i s o l a t e s ; the concentrates o f both p l a n t products were l i t t l e a f f e c t e d by NaCl. Data reported by Fleming et a l . r e f l e c t a response to NaCl; however, the type of i o n i s known t o a f f e c t the type o f response o f other p r o p e r t i e s (33) and p o s s i b l y the same i s true f o r water a b s o r p t i o n . Sucrose: E l g e d a i l y and Campbell (24) found sucrose, w i t h i n the c o n c e n t r a t i o n range used, t o have no s i g n i f i c a n t e f f e c t on water absorption o f three soy p r o t e i n i s o l a t e s . Fat Absorption Response P a t t e r n s The values f o r the soys were presented f i r s t (Table V) s i n c e most i n v e s t i g a t o r s used soy products as a reference f o r comparison o f the f a t absorption of other p l a n t products. L i n et a l . (17) examined the f a t absorption c a p a c i t i e s of v a r i o u s sunf l o w e r and soy products. A l l sunflower products ( f l o u r , conc e n t r a t e s , and i s o l a t e s ) bound more o i l than the soy counterpart. Fat absorption f o r the sunflower products ranged from 130 to 448% o f t h e i r weight on a 14% moisture b a s i s ; f a t absorption values f o r the soys ranged from 84 t o 154%. The sunflower prot e i n s appear to be more s t r u c t u r a l l y l i p o p h i l i c than the soy p r o t e i n s . I t seemed l i k e l y to the i n v e s t i g a t o r s t h a t the sunflower p r o t e i n s c o n t a i n numerous nonpolar s i d e chains that are b e l i e v e d to bind hydrocarbon c h a i n s , thereby c o n t r i b u t i n g to



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increased o i l a b s o r p t i o n . (Personal o b s e r v a t i o n of the average reported data f o r the f l o u r , concentrate, and i s o l a t e c a t e g o r i e s w i t h i n sunflower and soy products r e v e a l e d t h a t f a t absorption increased as p r o t e i n content i n c r e a s e d , sunflower products e x h i b i t i n g g r e a t e r f a t a b s o r p t i o n . A l s o w i t h i n the group o f soy i s o l a t e s and concentrates s t u d i e d , the percent f a t a b s o r p t i o n decreased as water s o l u b i l i t y of the product i n c r e a s e d . These p o s s i b l e r e l a t i o n s h i p s were not discussed.) Wang and K i n s e l l a (19) s t u d i e d the f a t a b s o r p t i o n , and other p r o p e r t i e s o f a l f a l f a l e a f p r o t e i n (ALP) concentrate and used the soy p r o t e i n concentrate and i s o l a t e Promosoy-100 and Promine-D,respectively, as the r e f e r e n c e s . The f a t absorption values are r e p o r t e d i n ml o i l / g sample. Converting these to percent f a t absorbed (based on the s p e c i f i c g r a v i t y of peanut o i l ) r e s u l t s i n values that are h i g h e r than those r e p o r t e d by L i n et a l . (17); t h i s was most evident i n the case of the i s o l a t e . A l l ALP products absorbed more o i l than the soy products. Acetone treatment of ALP r e s u l t e d i n reduced f a t a b s o r p t i o n ; ALP w i t h higher l i p i d contents absorbed more o i l . ALP e x t r a c t e d w i t h water and NaOH absorbed more o i l than those e x t r a c t e d w i t h NaCl or T r i s b u f f e r . These researchers (19) a t t r i b u t e f a t absorption to p h y s i c a l entrapment; a c o r r e l a t i o n of 0.95 was found between f a t a b s o r p t i o n and bulk d e n s i t y . However, more o i l was absorbed by the ALP than the soy products even though the products had s i m i l a r bulk d e n s i t i e s . Fat a b s o r p t i o n of rapeseed products was compared to t h a t of soy f l o u r s and concentrates (34). A l l rapeseed products e x h i b i t e d f a t a b s o r p t i o n values g r e a t e r than those of soy produ c t s . For both rapeseed and soy, f a t a b s o r p t i o n o f concentrates was g r e a t e r than that o f the f l o u r and meals. Values f o r the rapeseed i s o l a t e were s i m i l a r to those f o r the rapeseed concentrate. Textured soy f l o u r s were r e p o r t e d to have o i l a b s o r p t i o n values that ranged from 65 to 130% o f t h e i r dry weight w i t h s m a l l p a r t i c l e s absorbing more o i l than l a r g e ones. The maximum f a t absorption occurred w i t h i n 20 min for a l l p a r t i c l e s . Hutton (23) and Hutton and Campbell (26) evaluated the f a t a b s o r p t i o n c a p a c i t i e s o f a soy concentrate and i s o l a t e as a funct i o n o f temperature. (Values obtained f o r the ambient temperat u r e treatment, 22-25°C, are reported i n Table V.) Fat absorpt i o n was expressed on per gram of sample, a s - i s moisture, dryweight, and per gram of p r o t e i n bases as shown i n Table V I I I . Fat a b s o r p t i o n of the soy i s o l a t e (P-D) was g r e a t e r than t h a t of the concentrate (P-100) f o r a l l bases o f e x p r e s s i o n , but expression i n terms o f p r o t e i n content brought the f a t a b s o r p t i o n values o f the two products c l o s e r together. T h i s suggests t h a t the f a t absorption was a t t r i b u t a b l e p r i m a r i l y to the p r o t e i n . I t a l s o suggests t h a t the a d d i t i o n a l carbohydrate d i d not absorb as much o i l as the p r o t e i n and that the a b s o r p t i o n by the p r o t e i n was d i f f e r e n t f o r the two products. (That i s , the p r o t e i n was


194

PROTEIN

Table V I I .

FOODS

Isolate

a

%

pH 5.0 6.0 7.0 a

IN

Percent water a b s o r p t i o n values o f a soy concentrate and i s o l a t e as a f u n c t i o n o f ph (23). Concentrate


FUNCTIONALITY

257 433 1117

270 282 402

Weight o f concentrate equal t o weight o f i s o l a t e .

Table V I I I .

Fat a b s o r p t i o n o f a soy concentrate and i s o l a t e a t 22-25C ( 2 3 ) . Fat a b s o r p t i o n

Expression b a s i s

P-D

Sample wt., a s - i s Sample wt., dry P r o t e i n wt.

121.1 129.8 134.4

P-100

a 1

72.4 77.5 108.3

P-100

b 2

75.5 80.8 112.9

a

E q u a l sample weight r e l a t i v e t o P-D. ^Equal p r o t e i n weight r e l a t i v e t o P-D.



9.

H U T T O N

A N D

C A M P B E L L

195


Journal of Food Science

Figure 4.

Water absorption response surface for Promosoy-100 with variations in pH and temperature (20) x

30

40

50

60

100

TEMPERATURE ( ° C )

Journal of Food Science

Figure 5. Fat absorption (percent of protein weight) of Promosoy-lOOj (equal sample weight relative to Promine-D), Promosoy-100 (equal protein weight relative to Promine-D), and Promide-D held at 4°C, ambient temperature (22°-25°C) and 90°C: (A) P-100,; ( • ; P-100,, W P-D W g



196

PROTEIN

FUNCTIONALITY

IN

FOODS

p r i m a r i l y responsible, but e i t h e r the presence o f carbohydrate and/ or other c o n s t i t u e n t s i n the concentrate o r d i f f e r e n c e s i n p r o c e s s i n g o f the i s o l a t e and concentrate r e s u l t e d i n a s l i g h t l y d i f f e r e n t response by the p r o t e i n o f the two products.) The e f f e c t o f temperature and the i n t e r a c t i o n o f temperature and soy were s i g n i f i c a n t , as was soy product. The e f f e c t o f temperature on f a t absorption i s shown i n Figure 5. O v e r a l l , as temperature decreased from 90 t o 4°C, f a t a b s o r p t i o n increased. This c o u l d be a t t r i b u t a b l e t o increased v i s c o s i t y o f the o i l at decreased temperatures. P o s s i b l y , the high v i s c o s i t y of the system c o n t r i b u t e d t o g r e a t e r ease o f p h y s i c a l entrapment. Or perhaps the h i g h e r temperatures denatured the p r o t e i n i n some way t h a t r e s u l t e d i n decreased f a t a b s o r p t i o n . There was a temperature-soy i n t e r a c t i o n ; the i s o l a t e and concentrate d i d not respond s i m i l a r l y t o temperature v a r i a t i o n s . The i s o l a t e exhibi t e d maximum f a t absorption a t ambient temperature; the concentrate e x h i b i t e d a maximum at 4°C. T h i s suggests that somet h i n g other than p r o t e i n i s c o n t r i b u t i n g t o f a t a b s o r p t i o n . Food Product Performance The performance o f p r o t e i n a d d i t i v e s i n food products i s the u l t i m a t e t e s t o f f u n c t i o n a l i t y (7). F u n c t i o n a l performance, p a r t i c u l a r l y moisture a b s o r p t i o n , has been used as a c r i t e r i o n f o r s e l e c t i o n o f p r o t e i n a d d i t i v e s f o r food systems. Yet t h i s has f o r the most p a r t been a t r i a l - a n d - e r r o r s i t u a t i o n . The m a j o r i t y o f data on water and f a t absorption o f p l a n t p r o t e i n a d d i t i v e s i n food systems has i n v o l v e d the i n c o r p o r a t i o n o f such products i n t o comminuted meat systems. In r e l a t i o n t o water and f a t a b s o r p t i o n , meat systems are an e x c e l l e n t t e s t system. Several researchers (35, 36^ 37, 38) r e p o r t t h a t when soy products are combined w i t h ground meat products, t o t a l (moisture and f a t ) cooking l o s s e s are reduced as percent s u b s t i t u t i o n o f the a d d i t i v e i s increased. Seideman et a l . (39), on the other hand, reported t h a t beef p a t t i e s w i t h added soy r e t a i n e d more moisture but l o s t more f a t during cooking than d i d a l l - b e e f p a t t i e s . In products l i k e sausage and meat p i e s , p l a n t p r o t e i n a d d i t i v e s have been shown t o improve b i n d i n g o f the s t r u c t u r e and reduce moisture and f a t l o s s e s . This may be r e l a t e d t o the g e l l i n g and/or e m u l s i f i c a t i o n f u n c t i o n s , as w e l l a s , water and fat absorption. P r o t e i n a d d i t i v e s a l s o f i n d use i n numerous baked products. Soy f l o u r increases the s h e l f l i f e and freshness o f breads, pancakes, w a f f l e s , and cakes through enhanced moisture r e t e n t i o n (28, 40). A d d i t i o n o f soy f l o u r t o pancakes and doughnuts helps prevent excessive f a t a b s o r p t i o n during cooking (28). This phenomenon o f decreased f a t a b s o r p t i o n i s not w e l l understood. As presented, data are a v a i l a b l e on assessment o f water a b s o r p t i o n i n simple systems and on the i n c o r p o r a t i o n o f p r o t e i n a d d i t i v e s i n t o some food systems. F u n c t i o n a l p r o p e r t i e s i n



9.

H U T T O N



197

simple systems as r e l a t e d t o performance i n food systems have been s t u d i e d t o a l e s s e r degree (2, _3, 15^, 26^ 4^, 42) . ρ The most d e t a i l e d s t u d i e s were reported by Hermansson and Akesson (_3, 41) and Hermansson (42) i n which the p r o p e r t i e s o f a soy i s o l a t e , c a s e i n a t e , WPC, and model t e s t systems o f a d d i t i v e and lean beef o r pork were s t u d i e d . S o l u b i l i t y , s w e l l i n g , and v i s c o s i t y ( p r o p e r t i e s reviewed as r e l a t e d t o water absorption) were c o r r e l a t e d with moisture l o s s i n the raw systems. In cooked systems, the best p r e d i c t a b i l i t y o f meat t e x t u r e as a f f e c t e d by a d d i t i v e was a s t a t i s t i c a l model that i n c l u d e d t h e f u n c t i o n a l p r o p e r t i e s o f s w e l l i n g and g e l strength o f p r o t e i n additive dispersions. Torgersen and Toledo (15) assessed the r e l a t i o n s h i p between s o l u b i l i t y and water absorption o f WPC, peanut p r o t e i n , s i n g l e c e l l p r o t e i n (SCP), and chicken preen gland p r o t e i n and char a c t e r i s t i c s i n a comminuted meat system c o n t a i n i n g the v a r i o u s p r o t e i n a d d i t i v e s . P r o t e i n a d d i t i v e s w i t h high water absorption c a p a c i t i e s were c o r r e l a t e d w i t h more viscous raw mixtures and w i t h l e s s f a t and water r e l e a s e d on cooking. Simple system determination o f water absorption c a p a c i t y a t 90°C r a t h e r than at 78.5°C was the b e t t e r p r e d i c t o r o f water and f a t r e t e n t i o n i n the food system s t u d i e d . Conclusions The wide array o f p l a n t p r o t e i n products, methods, and terms used t o evaluate and describe f u n c t i o n a l p r o p e r t i e s makes i t d i f f i c u l t t o compare products and r e s u l t s o f separate s t u d i e s . In high p r o t e i n products, water and f a t absorption i s a t t r i b u t a b l e p r i m a r i l y t o the p r o t e i n . In other products, a d d i t i o n a l i n g r e d i e n t components have an e f f e c t . H y d r o p h i l i c polysaccharides g r e a t l y a f f e c t water absorption. Water absorp t i o n a l s o i s a f f e c t e d by product c o n c e n t r a t i o n , pH, temperature, and i o n i c s t r e n g t h . Fat absorption has been s t u d i e d l e s s e x t e n s i v e l y than water absorption but has been reported t o be a f f e c t e d by temperature, s i z e o f i n g r e d i e n t p a r t i c l e s , and degree o f denaturation o f the p r o t e i n . For both p r o p e r t i e s , f u n c t i o n a l performance o f the p r o t e i n product may be modified g r e a t l y by i n g r e d i e n t and/or food system c o n s t i t u e n t s . P l a n t p r o t e i n a p p l i c a t i o n s i n food systems have i n c l u d e d bakery and d a i r y products, s a l a d d r e s s i n g s , snack foods, and ground meat. The e f f e c t s o f p l a n t p r o t e i n products i n meat systems are r e l a t e d most o f t e n t o water and f a t absorption f u n c t i o n s . How ever, p r e d i c t a b i l i t y o f food system performance by simple system f u n c t i o n a l i t y t e s t s i s not i n e v i t a b l e . I t i s apparent t h a t the subject o f water and f a t absorption by p l a n t p r o t e i n s i s c h a r a c t e r i z e d and complicated by i n t e r r e l a t e d n e s s . The study o f r e l a t i o n s h i p s i s important and i s complicated by problems o f measurement; comparisons between s t u d i e s are hindered by the v a r i e t y o f methods and c o n d i t i o n s


198

PROTEIN

FUNCTIONALITY

IN

FOODS

used i n d i f f e r e n t l a b o r a t o r i e s . Some s t a n d a r d i z a t i o n should be undertaken. A few s t u d i e s i n which s o r p t i o n i n simple systems has been r e l a t e d t o performance i n food systems have been reported; more a r e needed. The e f f e c t s o f other food i n g r e d i e n t s on f u n c t i o n a l p r o p e r t i e s o f p r o t e i n s should be f u r t h e r i n v e s t i g a t e d . Obviously much remains t o be done.


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Hammonds, T. M.; Call, D. L. Agr. Εcon. 320, Cornell University Agr. Exp. Sta., Ithaca, Ν. Υ., 1970.

2.

Hermansson, A. -M. "Proteins in Human Nutrition," Ch. 27, Porter, J . W. G., and Rolls, Β. Α., Eds., Academic Press, London, 1973.

3.

Hermansson, A. -M.; Åkesson, C. J. Food Sci., 1975, 40, 595.

4.

Johnson, D. W. J. Am. Oil Chem. Soc., 1970, 47, 402.

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Kuntz, I. D., J. Am. Chem. Soc., 1971, 93, 514.

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Kinsella, J. E. J. Am. Oil Chem. Soc., 1979, 56, 242.

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Ryan, D. S.

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Kinsella, J. E. Crit. Rev. Food Sci. and Nutr. 219.

Adv. Chem. Series, 1977, 160, 67. 1976, 7,

10.

Mellon, E. F.; Korn, A. H.; Hoover, S. J . Am. Oil Chem. Soc., 1947, 69, 827.

11.

Huffman, V. L.; Lee, C. K.; Burns, E. E. J. Food Sci., 1975, 40, 70.

12.

Hagenmaier, R. J. Food Sci., 1972, 37, 965.

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Hermansson, A. -M. Lebensm.-Wiss. U. Technol., 1972, 5, 24.

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Hermansson, A. -M.; Sivik, B.; Skjöldebrand, C. Lebensm. -Wiss. U. Technol., 1971, 4, 201.

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Torgersen, H.; Toledo, R. T. J. Food Sci., 1977, 42, 1615.

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Quinn, J. R.; Paton, D. Cereal Chem., 1979, 56, 38.



9. HUTTON AND CAMPBELL


17.

Lin, M. J. Y.; Humbert, E. S.; Sosulski, F. W. J . Food Sci., 1974, 39, 368.

18.

Fleming, S. E.; Sosulski, F. W.; Kilara, Α.; Humbert, Ε. S. J. Food Sci., 1974, 39, 188.

19.

Wang, J. C.; Kinsella, J. E. J. Food Sci., 1976, 41, 286.

20.

Hutton, C. W.; Campbell, A. M. J. Food Sci., 1977, 42, 454.

21.

Hamm, R. Adv. Food Res., 1960, 10, 355.

22.

Sosulski, F. W. Cereal Chem., 1962, 39, 344.

23.

Hutton, C. W. "Functional properties of a soy isolate and a soy concentrate in simple systems as related to performance in a food system"; Dissertation, The University of Tennessee, Knoxville, Tenn., 1975.

24.

Elgedaily, Α.; Campbell, A. M. Unpublished data.

25.

James, C.; Campbell, A. M. Unpublished data.

26.

Hutton, C. W.; Campbell, A. M. J. Food Sci., 1977, 42, 457.

27.

Hermansson, A. -M. J. Am. Oil Chem. Soc., 1979, 56, 272.

28.

Wolf, W. J.; Cowan, J. C. Crit. Rev. Food Technol., 1971, 2, 81. Catsimpoolas, N.; Meyer, E. W. Cereal Chem., 1970, 47, 559. Catsimpoolas, N.; Meyer, E. W. Cereal Chem., 1971, 48, 150.

29. 30. 31.

Catsimpoolas, N.; Meyer, E. W. Cereal Chem., 1971, 48, 159.

32.

Hansen, J. R. J. Agric. Food Chem., 1978, 26, 301.

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Anderson, R. L.; Wolf, W. J.; Glover, D. J. Agr. Food Chem., 1973, 21, 251.

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Sosulski, F.; Humbert, E. S.; Bui, K.; Jones, J. D. J. Food Sci., 1976, 41, 1349.

35.

Adolphson, L. C.; Horan, F. E. Cereal Sci. Today, 1974, 19, 441.


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Anderson, R. H.; Lind, K. D. Food Technol., 1975, 29, (2), 44.

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Drake, S. R.; Hinnergardt, L. C.; Kluter, R. Α.; and Prell, P. A. J. Food Sci., 1975, 40, 1065.

38.

McWatters, K. H. J . Food Sci., 1977, 42, 1492.

39.

Seideman, S. C.; Smith, G. C.; Carpenter, Z. L. J. Food Sci., 1977, 42, 197.

40.

Levinson, Α. Α.; Lemancik, J. F. J. Am. Oil Chem. Soc., 1974, 51, 135A.

41.

Hermansson, A. -M.; Åkesson, C. J. Food Sci., 1975, 40, 603.

42.

Hermansson, A. -M. J. Food Sci., 1975, 40, 611.

RECEIVED

October 21, 1980.


Protein Functionality in Foods - American Chemical Society

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