Protein Functionality in Foods - American Chemical Society

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Downloaded by CALIFORNIA INST OF TECHNOLOGY on May 16, 2017 | http://pubs.acs.org Publication Date: March 6, 1981 | doi: 10.1021/bk-1981-0147.ch004

Texturization K. C. RHEE, C. K. KUO, and E. W. LUSAS Food Protein Research and Development Center, Texas Engineering Experiment Station, Texas A&M University System, College Station, TX 77843

Thermoplastic extrusion technology has been used to texturize many defatted vegetable protein ingredients, and produce many fibrous structures and meat-like textures. Such processes have been used extensively to prepare meat analogs (1, 2) which have found their widest application in formulation of foods for institutional markets (3). A primary disclosure of extrusion texturization of vegetable proteins was made by Atkinson (4). General descriptions of various extrusion processes have also been reported (1, 2, 5-14). Ingredients most commonly used in textured vegetable protein products are defatted soy flours or grits. Preferably, the defatted soy flour should contain a minimum of 50% protein with a nitrogen solubility index of 50 to 70, a maximum of 30% insoluble carbohydrate, and less than 1% fat (9). While the technology of protein extrusion has been rapidly developing, basic information concerning chemical and physical changes occurring in components of raw ingredients within the extruder barrel are still unknown. Most descriptions given are general, and lack details. According to Harper (15), the process begins with defatted soy flour, which is moistened and often mixed with a variety of additives. This mixture is fed to the extruder where it is worked and heated, causing protein molecules to denature and form new cross-linkages which result in a fibrous structure. The heated plasticized mass is forced through a die at the extruder discharge to form expanded texturized strands of vegetable proteins which have meat-like characteristics upon rehydration. However, the manner in which the protein was denatured and cross-linked to form the fibrous structure was not explained in this description. Kinsella (16), in his recent review on texturized proteins, described the texturization process as follows: the globular proteins (glycinins) in the aleurone granules become hydrated within the extruder barrel, are gradually unravelled, and are stretched by the shearing action of the rotating screw flites. The proteins become aligned in sheaths. In passing through the 0097-6156/81/0147-0051$09.50/0 © 1981 American Chemical Society

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

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d i e the p r o t e i n becomes f u r t h e r compressed and laminated l o n g i t u d i n a l l y , and i s denatured a t high temperatures. At the i n s t a n t of emergence from the d i e , pressure drops, moisture v a p o r i z e s and f l a s h e s o f f , and a i r - s p a c e vacuoles are produced w i t h i n the laminated extrudate. The c o o l i n g , accompanied by v a p o r i z a t i o n , allows r a p i d thermosetting or s o l i d i f i c a t i o n of the s t r e t c h e d p r o t e i n f i b e r s . A porous s t r u c t u r e , with p a r a l l e l arrays of lamellae of p r o t e i n f i b e r s , r e s u l t s . Again, how the p r o t e i n i s u n r a v e l l e d and the s t r e t c h e d p r o t e i n i s a l i g n e d i n sheaths were not e x p l a i n e d . Most of the research conducted to date has been concerned with o p t i m i z a t i o n of process c o n d i t i o n s , and e f f e c t of t h e i r changes on s e l e c t e d p h y s i c a l c h a r a c t e r i s t i c s and m i c r o s t r u c t u r e of the extrudate (17-22). L i t t l e i n f o r m a t i o n has been p u b l i s h e d concerning e f f e c t s of i n g r e d i e n t compositions on extrudate c h a r a c t e r i s t i c s . P r o t e i n s from d i f f e r e n t sources, v a r y i n g i n composition, molecular weight and s t r u c t u r e , are expected to s i g n i f i c a n t l y a f f e c t the product upon t e x t u r i z a t i o n . For example, i n c l u s i o n of g l u t e n (prepared from hard wheat) i n the feed mix y i e l d s a tough and chewy product, while use of g l u t e n from s o f t wheat y i e l d s a tender and f r i a b l e product (10). Reasons f o r these d i f f e r e n c e s are s t i l l unknown. The profound reason f o r having t h i s many unknowns i s a t t r i buted to the f a c t t h a t the "technology" of e x t r u s i o n t e x t u r i z a t i o n i s w e l l i n advance of the " s c i e n c e " . In-depth knowledge i n the " s c i e n c e " p o r t i o n of e x t r u s i o n t e x t u r i z a t i o n w i l l provide p r i n c i p l e s which can be used t o a c c u r a t e l y d e f i n e the t e x t u r i z e d p r o t e i n product. T h i s b a s i c s c i e n t i f i c knowledge should a l s o provide data which could be used to improve o p e r a t i n g e f f i c i e n c y of extruders, and serve as a b a s i s f o r producing t e x t u r i z e d p r o t e i n foods, with d e s i r e d c h a r a c t e r i s t i c s f o r s p e c i f i c product a p p l i c a t i o n s , from a wide v a r i e t y of raw i n g r e d i e n t s .


f

EXPERIMENTAL PROCEDURES P r e p a r a t i o n of Raw M a t e r i a l s . Defatted soy f l o u r s used i n t h i s study were Soya Fluff-200W (Central Soya Inc., F o r t Wayne, IN) and E x t r a Acted Soy F l o u r 200-1 (A.E. S t a l e y , Decatur, I L ) . These two f l o u r s met the requirements proposed by Smith {9) . Soy i s o l a t e was prepared by the i s o e l e c t r i c p r e c i p i t a t i o n procedure developed at the Food P r o t e i n Research and Development Center, Texas A&M U n i v e r s i t y System (23). A commercial soy i s o l a t e , Promine F (Central Soya Inc., F o r t Wayne, IN), was a l s o used i n t h i s study. M o d i f i c a t i o n of Raw M a t e r i a l s . In order to vary the prot e i n and s o l u b l e sugar contents, p o r t i o n s of soy f l o u r (Extra Acted Soy F l o u r 200-1) were r e p l a c e d with v a r i o u s amounts o f sucrose and soy p r o t e i n i s o l a t e (Promine F ) . L e v e l s of



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replacement were 5, 10 and 15% f o r sucrose, and 10, 20, 40 and 60% f o r soy i s o l a t e , r e s p e c t i v e l y . The pH of soy f l o u r (pH 6.6) was a l t e r e d by spraying water c o n t a i n i n g p r e c a l c u l a t e d amounts o f a c i d (HC1) or base (NaOH). When 1:3 (w/v) s l u r r i e s were prepared from these m o d i f i e d f l o u r s , the a c t u a l pH values obtained were 5.3, 5.6, 6.6, 8.0 and 9.0, respectively. To vary the Nitrogen S o l u b i l i t y Index (NSI) of the Soya F l u f f 200W (NSI 65), 600-g batches o f f l o u r were heated on baking pans i n an oven (135°C) f o r 2, 4 and 12 h r . These heat treatments reduced the 65% NSI f l o u r to 51, 46 and 14% NSI, r e s p e c t i v e l y . E x t r a Acted Soy F l o u r 200 I , with an NSI of 55.8%, was a l s o i n c l u d e d i n t h i s study without any heat treatment. Ionic s t r e n g t h of the Soya F l u f f 200W was v a r i e d by adding v a r i o u s amounts of NaCl and CaCl2. Amounts of each s a l t added to the f l o u r were 0.2, 1 and 2%, based on f l o u r weight. Molecular weights of soy f l o u r p r o t e i n s were e n z y m a t i c a l l y modified by the f o l l o w i n g method: (1) 20% soy f l o u r s l u r r y (w/v, pH 8) was shaken f o r 30 min i n a 50°C water bath; (2) Papain ( W a l l e r s t e i n , D e e r f i e l d , IL) (1:1,000, w/v, papain to f l o u r ) was added t o the s l u r r y a f t e r shaking; (3) d i g e s t i o n was continued f o r 10 min a t 50°C; (4) the d i g e s t e d s l u r r y was heated r a p i d l y to 85°C i n a b o i l i n g water bath to stop enzyme a c t i v i t y ; (5) a f t e r c o o l i n g , pH of s l u r r y was adjusted back to 6.6 f o l l o w e d by f r e e z e d r y i n g ; and (6) d r i e d product was then ground (100 mesh). A c o n t r o l was prepared i n the same manner without the enzyme added. In an attempt t o determine the p o s s i b l e chemical r e a c t i o n s between f r e e amino (NH2) and c a r b o x y l (COOH) groups during t e x t u r i z a t i o n , f l o u r p r o t e i n was c h e m i c a l l y m o d i f i e d with v a r i o u s amounts of s u c c i n i c and a c e t i c anhydrides to b l o c k the s e l e c t e d number of f r e e amino and c a r b o x y l u n i t s to l i m i t or i n h i b i t r e a c t i o n between these two groups. Soy f l o u r was s u c c i n y l a t e d according t o the method of Groninger (24i) . F i f t y (50) grams of soy f l o u r was d i s p e r s e d i n 250 ml of water, and v a r i o u s amounts (1.25, 2.50 and 3.75 g) of s u c c i n i c anhydride were added t o the d i s p e r s i o n at 0.5 g increments during constant stirring. The pH of the d i s p e r s i o n was maintained a t 7.5 with 4N NaOH. A f t e r the pH had been s t a b i l i z e d , the d i s p e r s i o n was d i a l y z e d a g a i n s t d i s t i l l e d water (4°C, 24 hr) to remove the excess s u c c i n i c anhydride. The s u c c i n y l a t e d soy f l o u r was then recovered by l y o p h i l i z a t i o n . The a c e t y l a t i o n procedures were s i m i l a r to s u c c i n y l a t i o n , except amounts of a c e t i c anhydride added t o each 50 g of soy f l o u r were 2.5, 3.75 and 10 ml. Dial y s i s was continued f o r 72 hr with changing of d i s t i l l e d water every 24 h r . To i n v e s t i g a t e the hypothesis t h a t d i s s o c i a t i o n of d i s u l f i t e bonds i n t o subunits might be a r e a c t i o n o c c u r r i n g d u r i n g formation of t e x t u r i z e d soy f l o u r (25), two d i s u l f i d e bond reducing agents (Na2S03, and cysteine-HCl) were added to soy


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f l o u r s at three concentrations (0.1, 0.2, 0.5% based on f l o u r weight) p r i o r to e x t r u s i o n . A strong o x i d i z i n g agent, KIO3, thought to be e f f e c t i v e i n reducing e x t e n s i b i l i t y of wheat f l o u r dough by enhancing d i s u l f i d e l i n k a g e s , was a l s o added to soy f l o u r at 0.01 and 0.05% concentrations. S u r f a c t a n t s have been, r e p r o t e d l y , used to prevent extensive p u f f i n g of extruded c e r e a l products. I t was found i n these s t u d i e s t h a t s u r f a c t a n t s could e f f e c t i v e l y i n h i b i t g e l a t i n i z a t i o n of c e r e a l s t a r c h . However, e f f e c t of s u r f a c t a n t s on p r o t e i n t e x t u r i z a t i o n has not been reported. Two types of s u r f a c t a n t s , sodium s t e a r o y l - 2 - l a c t y l a t e and calcium s t e a r o y l - 2 - l a c t y l a t e (at l e v e l s of 0.2 and 0.4% based on the weight of the f l o u r ) , were mixed with soy f l o u r p r i o r t o e x t r u s i o n . A yeast p r o t e i n (Torutein, manufactured by Amoco Inc.), claimed to be an e x t r u s i o n h e l p e r although i t s f u n c t i o n i s not known, was added. In p r e l i m i n a r y s t u d i e s , i t was found t h a t t h i s p r o t e i n gives r e s u l t s s i m i l a r to a s u r f a c t a n t when added at 1% and 2% l e v e l s . Texturization Processing, A Wenger Model X-5 l a b o r a t o r y extruder was used i n t h i s i n v e s t i g a t i o n . This u n i t has a 1-inch diameter e x t r u s i o n b a r r e l , with a b a r r e l length to diameter r a t i o of approximately 18:1. The b a r r e l i s composed of 8 jacketed s e c t i o n s , and i s f i t t e d w i t h a sidefeeder and a terminal e x t r u s i o n d i e p l a t e . Diameter of the d i e o r i f i c e i s 0.4 cm. The screw i s a TSP type o r i g i n a l l y designed and manufactured by Wenger f o r e x t r u s i o n of soy f l o u r . Conditions used f o r e x t r u s i o n t e x t u r i z a t i o n of raw i n g r e d i e n t s were: screw speed, 625 rpm; feed r a t e , 160 g/min; and d i s t a n c e between end p l a t e and screw end, 1/4 i n c h . The m i n i mum b a r r e l temperature t o o b t a i n a product s u r v i v i n g a u t o c l a v i n g was around 138°C. Higher temperatures increased p u f f i n g of the product. However, steam m i g r a t i o n t o the feed s e c t i o n caused blockage. To minimize t h i s blockage problem the f i r s t and second s e c t i o n s of the extruder b a r r e l were not heated. In order to achieve a constant temperature of 138°C, steam pressures were c o n t r o l l e d at 2.7 x 10^ kg/m . A l l raw m a t e r i a l s were premoistened to 25 + 0.5% moisture, and e q u i l i b r a t e d overnight p r i o r to e x t r u s i o n . The Hand Press (HP) t e x t u r i z e r described by Sterner and Sterner (26) was used to prepare t e x t u r i z e d products from chemically modified soy f l o u r s . Although the Hand Press does not produce shearing a c t i o n during t e x t u r i z a t i o n , products prepared under proper c o n d i t i o n s are morphologically and r h e o l o g i c a l l y s i m i l a r t o e x t r u s i o n t e x t u r i z e d products (27). The Hand Press t e x t u r i z e r c o n s i s t s of a heated c i r c u l a r recessed bottom p l a t e i n t o which twenty to twenty-five grams of sample are placed. A heated top p l a t e i s then placed over the sample, and a c o n t r o l l e d pressure a p p l i e d to the top p l a t e by a l e v e r mechanism, at a known temperature, f o r a predetermined length of time (sec). The pressure i s then r a p i d l y r e l e a s e d by removing 2


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the hand from the l e v e r . Rapid pressure r e l e a s e permits i n stantaneous v a p o r i z a t i o n o f moisture t o steam, which r e s u l t s i n a textured wafer-shaped product. In t h i s Hand Press study a l l raw i n g r e d i e n t s were processed under the c o n d i t i o n s optimized f o r d e f a t t e d soy f l o u r : temperature (143°C-160°C); pressure, 250-300 p s i ; and r e t e n t i o n time, 10 sec f o r 25-g samples with f l o u r moisture contents o f 25%. Assay Methods f o r E v a l u a t i o n of F l o u r s and T e x t u r i z e d Products• Nitrogen s o l u b i l i t y index o f soy f l o u r a t n e u t r a l pH was determined by the O f f i c i a l and T e n t a t i v e Methods o f the American A s s o c i a t i o n of C e r e a l Chemists (29). Water h o l d i n g c a p a c i t y (WHC) of t e x t u r i z e d products was determined by a r e l a t i v e l y f a s t , easy and repeatable method. Extrudates were f i r s t d r i e d t o 5 t o 7% moisture content, and reduced t o 4-6 mesh s i z e p a r t i c l e s . To 5 grams of extrudate, 25 ml of water was added. A f t e r one hour h y d r a t i o n , the hydrated sample and r e s i d u e water were f i l t e r e d through No. 1 Whatman f i l t e r paper. The WHC was expressed as: WHC =

Grams of water h e l d Gram o f dry sample

Water r e t e n t i o n c a p a c i t y (WRC), which i s d e f i n e d as grams of water r e t a i n e d per gram o f dry extrudate a f t e r h y d r a t i o n and c e n t r i f u g a l f i l t r a t i o n , was determined by the f o l l o w i n g procedure. One (10) gram o f d r y s o l i d ( p a r t i c l e s i z e o f 4-6 mesh) was weighed onto the s i n t e r e d g l a s s f i l t e r and hydrated f o r one hour with 10 ml water. A tared thimble, c o n t a i n i n g the sample and water, was then placed i n a conical-shaped p l a s t i c c e n t r i f u g e tube. The assembly was then spun f o r 15 min a t 650 x g i n an I n t e r n a t i o n a l No. 2 c e n t r i f u g e . The WRC was then c a l c u l a t e d as:

WRC =

Weight g a i n o f sample Weight o f dry sample

To determine bulk d e n s i t y (BD), extrudates o r Hand Press T e x t u r i z e d products were d r i e d t o 5-7% moisture, and ground. Product passing through a U.S. No. 4 Sieve but r e t a i n e d on the U.S. No. 6 Sieve, was f i l l e d i n 100 ml v o l u m e t r i c f l a s k s , and tapped l i g h t l y f o r 20 times. Weight of the 100 ml sample was determined, and the bulk d e n s i t y was then expressed as grams per l i t e r . An I n s t r o n T e s t i n g System (Model 1122), f i t t e d with a 10 cm s i x - w i r e g r i d (Ottawa Texture measuring system, OTMS c e l l ) was used t o determine r h e o l o g i c a l p r o p e r t i e s . A loading r a t e of 50 mm/min and a c h a r t speed of 500 mm/min r e s u l t e d i n a w e l l defined force-deformation curve. Force a t the b i o y i e l d p o i n t and the area under the curve were c a l c u l a t e d . These values were then converted i n t o maximum s t r e s s , work and s p e c i f i c work v a l u e s : 2


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I N FOODS

2

s t r e s s (Newton (n)/cm )=force per u n i t area o f t e s t sample:Work (N^-cm/cm ) =work p e r u n i t value of t e s t sample; and s p e c i f i c work (N-cm/g)=work per u n i t weight of t e s t sample. Samples f o r r h e o l o g i c a l e v a l u a t i o n by the Instron were prepared by f i r s t reducing p a r t i c l e s i z e t o minus 4 plus 6 meshes, and r e h y d r a t i n g product with twice the amount o f water (w/w) f o r one hour i n a covered glass beaker. The rehydrated samples were then r e t o r t e d a t 121°C (15 psi) f o r 30 min. The r e t o r t e d samples were cooled i n a running tap water bath, and h e l d i n the room housing the Instron f o r 30 min before t e s t i n g . F i v e 7.5-g p o r t i o n s of samples were weighed onto the Ottawa c e l l f o r the Instron measurement (30). P r o t e i n s o l u b i l i t i e s o f soy f l o u r and extrudates i n the f o l l o w i n g s o l v e n t systems were determined by the m i c r o - K j e l d a h l method (29). A p o r t i o n (0.1 g) o f f i n e l y - g r o u n d sample (No. 60 sieve) was extracted with 9.9 ml of s o l v e n t f o r 1 hr a t room temperature followed by c e n t r i f u g a t i o n and f i l t r a t i o n . An a l i q u o t of the supernatant was used f o r n i t r o g e n d e t e r m i n a t i o n . A f a c t o r o f 6.25 was used t o convert n i t r o g e n content t o p r o t e i n . Solvent systems used i n c l u d e d : (1) 0.01M phosphate b u f f e r , pH 7.2; (.2) 0.01M carbonate b u f f e r , pH 10.0; (3) Phosphate b u f f e r + 1% 2-mercaptoethanol (2-ME); (4) Phosphate b u f f e r + 1% sodium dodecyl s u l f a t e (SDS); and (5) Phosphate b u f f e r + 1% 2-ME+ 1% SDS. The extent o f s u c c i n y l a t i o n and a c e t y l a t i o n was determined by the t r i n i t r o b e n z e n e s u l f o n i c a c i d (TNBS) method as described by H a l l e t a l . (3_1) . P r o t e i n (5 mg) i s o l a t e d from chemically modified and c o n t r o l soy f l o u r i n 0.8 ml o f aqueous s o l u t i o n was added t o 1 ml of 4% NaHC03, followed by a d d i t i o n of 0.2 ml o f 2,4,6-trinitrobenzenesulfonic a c i d (12.5 mg/ml). The r e a c t i o n mixture was incubated a t 40°C f o r 2 hr, and 3.5 ml o f 36% HC1 was added. The tubes were stoppered and kept a t 110°C f o r 4 h r . A f t e r c o o l i n g t o room temperature (24°C), volume of s o l u t i o n was made up t o 10 ml with d i s t i l l e d water, and contents were e x t r a c ted twice with anhydrous d i e t h y l ether. The tubes were unstoppered and h e l d a t 40°C t o allow the r e s i d u a l ether t o evaporate. The absorbance o f the yellow (eTNP l y s i n e ) s o l u t i o n was measured a t 415 nm a g a i n s t a blank. The extent of m o d i f i c a t i o n was c a l c u l a t e d from the d i f f e r e n c e i n absorbance between the c o n t r o l and modified soy p r o t e i n .


3

o % Modification

A =

unmodified -

A

modified

unmodified The sodium d o d e c y l s u l f a t e Polyacrylamide Gel E l e c t r o p h o r e s i s (SDS-PAGE) was c a r r i e d out according t o the method o f Weber and Osborn (32). For the f i r s t 30 min o f e l e c t r o p h o r e s i s , a current of 4 mA per g e l (10 cm long) was used, and then increased t o 8 mA per g e l f o r the subsequent 6 h r . A f t e r e l e c t r o p h o r e s i s , the dye f r o n t on the g e l was marked with ink, and the g e l was s t a i n e d with 2.5% Coomassie B r i l l i a n t


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Blue s o l u t i o n i n a mixture o f methanol and g l a c i a l a c e t i c a c i d and water (5:1:5) f o r 2 h r . F i n a l l y , the s t a i n e d g e l s were des t a i n e d i n a s o l u t i o n c o n t a i n i n g 5% methanol and 7.5% a c e t i c a c i d i n water u s i n g an automatic e l e c t r i c d e s t a i n e r . For d i s c g e l e l e c t r o p h o r e s i s (DGE), a low c u r r e n t (1.5 mA per gel) was a p p l i e d t o the g e l during the i n i t i a l p e r i o d (when the sample was s t i l l i n the s t a c k i n g gel) and the amperage was i n c r e a s e d t o 3 mA per g e l as soon as the samples penetrated i n t o the running g e l . The r e s t of the procedure was the same as the SDS-PAGE. P r e p a r a t i o n s and Examinations o f Samples f o r Transmitted L i g h t (TLM), Transmission E l e c t r o n (TEM) and Scanning E l e c t r o n (SEM) M i c r o s c o p i e s , Methods t o prepare specimens f o r micros c o p i c s t u d i e s developed by Mollenhauer and T o t t e n (_33) and modified by Cegla e t a l . (30) were f o l l o w e d . TLM examinations were conducted on a Z e i s s Standard 19 Research microscope. TEM examinations were conducted on a H i t a c h i HS-8 a t Kv on 600-800A s e c t i o n s prepared according t o Galey and N i l s s o n (34). SEM examinations were conducted on JOEL JSM-35 a t 25 kv.

0

FACTORS AFFECTING EXTRUSION TEXTURIZATION PROPERTIES OF SOY FLOUR E f f e c t s o f P r o t e i n Contents. P r o t e i n contents of soy f l o u r s were m o d i f i e d by adding v a r i o u s amounts o f sucrose o f soy p r o t e i n i s o l a t e (Promine F ) . Extrudates o f sucrose-added soy f l o u r s were not s i g n i f i c a n t l y d i f f e r e n t from the c o n t r o l i n e x t e r i o r morphology. Scanning e l e c t r o n micrographs showed that sucrosec o n t a i n i n g extrudates were s i m i l a r t o the c o n t r o l i n i n t e r i o r s t r u c t u r e (Figure 1 ) . However, s u c r o s e - c o n t a i n i n g extrudates had lower s t r e s s and r e s i l i e n c e values than the c o n t r o l when measured with I n s t r o n , but they had higher bulk d e n s i t i e s and lower water r e t e n t i o n and h o l d i n g c a p a c i t i e s than the c o n t r o l (Table I ) . I n c r e a s i n g the p r o t e i n content of raw i n g r e d i e n t s from 54.3% t o 57.9% d i d not s i g n i f i c a n t l y change the i n t e r i o r and e x t e r i o r morphologies of extrudates. P h y s i c a l and r h e o l o g i c a l p r o p e r t i e s of these two products were a l s o s i m i l a r . However, when the p r o t e i n content was i n c r e a s e d t o 61.8% or h i g h e r , a l l extrudates appeared l a r g e r i n diameter, smoother i n s u r f a c e morphology, lower i n bulk d e n s i t y and higher i n water r e t e n t i o n and h o l d i n g c a p a c i t i e s than the c o n t r o l . E f f e c t s of N i t r o g e n S o l u b i l i t y Index. N i t r o g e n s o l u b i l i t y indexes of soy f l o u r ( i n i t i a l NSI 65%) were m o d i f i e d by h e a t i n g i n an oven (135°C) f o r 2, 4 and 12 hr p r i o r t o e x t r u s i o n . These treatments r e s u l t e d soy f l o u r s with NSI values o f 51, 46 and 14%, r e s p e c t i v e l y . The NSI-14 f l o u r was found unusable f o r e x t r u s i o n . The o r i g i n a l f l o u r (NSI 65%) produced extrudates having low



PROTEIN FUNCTIONALITY I N FOODS

Figure 1. SEMs of extrusion TSFs varying in protein (P) and soluble sugar (S) contents. (1) 57.9% P and 12.2% S, (2) 61.8% P and 6.2% S, (3) 69.3% P and 8.8% S, (4) 75.8% P and 6.2% S. Note that they are significantly different in air cell sizes.


Cherry; Protein Functionality in Foods ACS Symposium Series; American Chemical Society: Washington, DC, 1981. 8.40b 10.90a

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— Means with d i f f e r e n t l e t t e r i n the same column d i f f e r s i g n i f i c a n t l y a t P

Protein Functionality in Foods - American Chemical Society

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