Soy isolate

Table V shows the composition of the liquid meals for this study. As in the previous study, two levels each of cottage cheese and beef were fed to the subjects. In addition, 45 g of protein from soy isolate was also fed. The phytic acid content of this meal was 126 mg. A basal diet containing all nutrients except protein was also included in this study. It was necessary to reduce the fat content of the basal diet for palatability the total energy for this meal only was 250 kcal. In this study, the calcium and phosphorus levels of each meal were equalized across all levels and sources of protein. Levels of other meal components were maintained as constant as possible and are shown at the bottom of Table V.

Rakosky ( ) reported that if a 25% shrink were obtained with an all meat product, the shrink in a meat product augmented with soy concentrate would be about 22.5%, or a 10% reduction in shrink. Use of textured soy rather than soy concentrate (Table IV) has been shown to reduce shrink in beef patties ( ,7 ). In a comparison of textured soy, soy concentrate and soy isolate, Berry et al. (7) found isolates gave the lowest cooked yields. In that study, cooking yields were directly related to the amount of dry soy in the ground beef-soy formulations. The greater quantity of soy (and correspondingly less water) in the textured soy flour formulation increased moisture retention and decreased total cooking loss. 

Wolf (8) attributed the water binding by soy flour not only to the presence of the proteins but also to the polysaccharides which are present. Kotula and Rough (6) demonstrated that ground beef patties extended with soy flour or concentrate were more tender than the all beef patties. Berry et al. (7 ) found patties made with soy flour or concentrate to be more tender than all-beef patties or patties formulated with soy isolate. The dilution... 

In the study by Thompson, et al. (11), the ml of gel released per 100 g emulsion for the reference emuTsion without soy, with soy isolate (SIF), soy concentrate (SCF) or soy flour (SF) was 6.07, 5.83, 5.49 and 3.08, respectively, when the hydration ratios were 1 4 (flourrwater) for SIF, 1 3 for SCF and 1 2 for SF. The ml gel released per 100 g emulsion containing 10, 15, 20, and 25% soy protein was 6.70, 5.01, 3.94 and 3.57, respectively. When soy protein concentrate was incorporated into an emulsion at the 3.5% level, the processing yields, textural profile and sensory textural attributes of frankfurters were not different among the products with and without added soy concentrate (13). An objective measure of compression and shear modulus indicated that soy protein concentrate incorporated into frankfurters at the 3.5% level had no effect on batter strength or texture ( M). The addition of a cottonseed protein to frankfurters to replace 5, 10 or 15% of the meat resulted in higher pH, less cured color, less firmness of skin, softer texture and reduced desirability as judged by a sensory panel (J5J. 

Significantly decreased iron balances with soy isolate diet tendency for zinc balances to decrease with increased phytic acid level (40)... 

Simpson et al. (24) did not observe increased non-heme iron absorption when dephytinzed bran was included in a test meal compared to the non-dephytinized bran. Removal of phytic acid from soy protein likewise did not improve non-heme absorption (38). Decreased iron balances, observed by Bodwell et al. (40) with soy isolate diets, did not appear to be associated with the level of phytic acid a tendency for zinc balances to decrease with increased phytic acid was observed. 

In a series of studies, Cook and co-workers (48,49,50) observed a marked decrease in non-heme iron absorption when soy protein was added to beef or protein mixtures or when soy protein was consumed as the primary protein source in test meals and compared to the effects of including egg albumen or beef alone in the test meal (Table III) Hallberg and Rossander (38J, however, found less of an effect when total iron absorption (heme plus non-heme iron) was considered. Likewise, in a study in which reconstituted textured soy was used to replace 30% of the beef, the absorptions of total iron were not greatly altered (51). In a study by Stekel et al. (52), replacing part of the beef with soy isolate or adding hydrated isolate to beef decreased non-heme iron absorption from 12.4% to 9.2 and 9.3%, respectively. In a related study, non-heme and total iron absorptions were low when soy isolate was the major protein source. 

Five men fed dried skim milk (DSM), DSM plus soy isolate or soy isolate diets, each for 14-day periods "adequate" levels of ascorbic acid provided... 

Diets based on textured soy, soy isolate or animal protein each diet fed to 16 or 17 men for 35 days 60mg ascorbic acid/day... 

Added 100 mg ascorbic acid to soy isolate or egg albumen semipurified test meals 9 adult men... 

Semi-purified test meals, fed to 7 men contained (a) soy isolate, (b) soy isolate,... 

Absorptions of non-heme iron were (50) 0.56 and 3.20, (soy isolate, isolate + ascorbic acid), 5.05 and 10.19 (albumen, albumen + ascorbic acid)... 

Zinc. Some recent studies on the effects of soy protein on zinc utilizaton are summarized in Table IV. Young and Janghorbani (4 4) and Istfan et al. (46) compared the effects of soy isolate or soy concentrate and dried skim milk as protein sources in multi-day feeding periods. Zinc absorptions, measured by fecal monitoring of the extrinsic label given, were equivalent and no deleterious effects of soy protein were observed. In a second study, Istfan et al. (47) fed egg protein diets for 10 days and then a soy concentrate diet for 82 days. Zinc absorptions were not decreased by feeding the soy concentrate diet. 

Janghorbani et al. (58) fed isonitrogenous diets to 10 subjects for 12 days. Both an intrinsic label (chicken) and extrinsic labels were used. Zinc absorptions from an all-chicken diet and from a 50% chicken-50% soy isolate diet were equivalent. Solomons et al. (59) fed 5 or 10 subjects diets in which milk, soy isolate, and beef (or mixtures of these) were protein sources for the milk and/or soy diets, absorptions were similar "fractional" absorptions from beef bologna may have been higher than from soy bologna (Table IV). 

Ten subjects fed (12 days) isonitrogenous diets with all protein from chicken meat or 50% from chicken and 50% from soy isolate intrinsic (chicken) and extrinsic labels used (fecal monitoring method)... 

Subjects (16 or 17) consumed meals with >70% of protein from (a) textured soy, (b) soy isolate or (c) animal protein sources, each for 35 days... 

Preparation of Protease-Treated Proteins. The proteolysis of soy isolate was carried out by introducing 6 mL pronase E (mg/mL) to a well dispersed mixture of 12 g Mira Pro 111 in 760 mL water. Different levels of proteolysis were achieved by reaction at 50 °C for various periods of time. The reaction was stopped by heating at 100 C for 3 min, and the modified protein was then recovered by lyophilization. 

Soy isolate was prepared by the isoelectric precipitation procedure developed at the Food Protein Research and Development Center, Texas A M University System (23). A commercial soy isolate. Promine F (Central Soya Inc., Fort Wayne, IN), was also used in this study. 

Possible Roles of insoluble Carbohydrates in Texture Development. Based on data obtained frcm soy isolate-soy hull blend texturization experiments, insoluble carbohydrates and crude fiber play an important role in modulating the morphology of final texturized products (Figures 11-14). Insoluble carbohydrates, because of their plastic response to deformation, control the type of alveolation developed during processing. 

Figure 10. SEMs comparing air cell size and thickness of nonextrusion TSF (I), soy concentrate (2), soy isolate (3), and aqueous-extracted soy flour (4)...

Figure 14. SEMs of nonextrusion textured soy isolate with different amounts of CF (1) alveolate morphology and (2) air cell cuticle of 5.3% CF products (3) alveolate morphology and (4) air cell cuticle of 9.6% CF products and (5) alveolate morphology and (6) air cell cuticle of 13.1 % CF products.

In contrast. Figure 2 shows that the percentage of protein in solution for soy isolates remains constant as the amount of added protein is increased (1 ). In other words, the amount of protein in solution increases linearly with increasing amounts of added protein. This behavior is observed for all the isolates we have studied up to the highest concentration of 18 percent. Thus, soy isolates behave as if they are composed of a completely soluble fraction (A) and a completely insoluble fraction (B). Upon the addition of solvent, the soluble fraction (A) dissolves completely while the insoluble fraction (B) remains unchanged. There is no equilibrium established between A and B such that, if B is separated from A and reslurried in additional amounts of solvent, no additional protein will go into solution. (More precisely, no evidence of microscopic reversibility was found on the time scale of the experiment,... 

Hermansson ( ) has studied the effect of Nal, NaCl, NaC2H302, Na2S04 and CaCl2 on the solubility of an isolate prepared under mild conditions. There has been no corresponding work reported for denatured soy isolates. Thus, what follows is an evaluation of the effects of neutral salts on the solubility of native and denatured soy isolates. 

Class III Protein solubility is decreased (salting out) and is then increased (salting in) by increasing salt concentration. Except for the soy isolates, there are no other proteins to my knowledge that exhibit this type of solubility behavior. However, in the related polymeriza-... 

For measuring water absorption by the excess water method, the techniques developed by Janicki and Walczak (described by Hamm, 21) for meats and by Sosulski (22) for wheat flour are modified. Lin et al. (17) modified the Sosulski technique for use with sunflower and soy meal products. This modified procedure has been employed for much of the research on water absorption of plant protein additives. Water absorption capacities of a soy flour, two soy concentrates, and two soy isolates were compared by Lin et al. (17) to those of a sunflower flour, three sunflower concentrates, and one sunflower isolate. The percent water absorption of the soy products increased as the total protein content of the samples increased from flour to isolate. The soy flour absorbed 130% water, the soy concentrates absorbed an average of 212% water, and the soy isolates absorbed an average of 432% water. No calculations were made, however, that related the percent water absorbed to protein content of the samples. The sunflower products, though similar in protein content, did not respond in the same magnitude or direction as the soy products. 

The water absorption of alfalfa leaf protein (ALP) extracted and prepared by different methods was compared to that of a soy concentrate and a soy isolate (19). The method for determining water absorption was that of Lin et al. (17) and Fleming et al. 

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