Protein concentrate, from soybeans

Phytic acid and camosine (histidine-containing dipeptide), obtained from cereal and meat by-products, are effective inhibitors of hpid oxidation by several mechanisms, including metal inactivation and free radical quenching. Uric acid obtained from the decomposition of adenosine triphosphate in muscle also inhibits lipid oxidation by the same mechanisms. However, the importance of uric acid as an endogenous antioxidant in muscle foods is not clear. Various protein concentrates from soybeans, cottonseed and peanuts inhibit hpid oxidation in muscle foods. In addition to their iron binding activity, these crade extracts contain complex polyphenolic flavonoids that have potent antioxidant activity. 

Johnson, L.A. Process for Producing Improved Soy Protein Concentrate from Genetically Modified Soybeans, U.S. Patent 5,936,069 (1999). 

Researchers are attempting to bolster traditional protein sources and to develop entirely new proteins, with their efforts centered around the following approaches and protein sources (1) improvement of traditional sources through gene tic manipulation, (2) fortification with synthetic nutrients, or addition of protein concentrates from fish, oilseeds, and other foods, (3) use of the versatile soybean, and (4) development of single cell protein technology. 

The mmen is not functional at birth and milk is shunted to the abomasum. One to two weeks after birth, the neonate consumes soHd food if offered. A calf or lamb that is nursing tends to nibble the mother s feed. An alternative method of raising the neonate is to remove it from its mother at a very young age, <1 week. A common example of an early weaning situation is the dairy calf that is removed from the cow soon after birth so that the cow s milk supply might be devoted entirely to production. In this instance, the neonate requires complete dietary supplementation with milk replacer. Sources of milk replacer protein have traditionally included milk protein but may also include soybean proteins, fish protein concentrates, field bean proteins, pea protein concentrates, and yeast protein (4). Information on the digestibiUty of some of these protein sources is available (4). 

In order to produce soy protein, soybeans are first dehulled, flaked, and defatted to make white flakes . Soy protein concentrates are obtained by removing a portion of the carbohydrates from defatted and dehulled soybeans. Alcohol extraction is the method most commonly used to manufacture soy protein concentrates even though it results in the loss of isoflavones. Soy protein concentrates retain most of the fiber in the original soybean and must contain at least 65% protein on a moisture-free basis to meet quality standards. The most concentrated source of soy protein is soy protein isolates (or isolated soy protein, ISP), which is required to be at least 90% protein on a moisture-free basis. It is heat-treated during processing to insure inactivation of trypsin inhibitors. Most isolated soy protein is manufactured by water extraction from defatted and dehulled soybeans and it retains the natural isoflavones. 

Figure B3.5.5 Near-UV CD spectra. (A) Bovine a -casein peptide under a variety of conditions (data from Alaimo et al., 1999). Peptide concentration 0.631 mg/ml in 2 mM PIPES, 4 mM KCI, pH 6.75 scan rate 40 sec/nm path length 10 mm bandwidth 1.5 nm. The loss of aromatic dichroism with increasing temperature indicates denaturation, which is, however, not complete at 70°C or in 6 M guanidine hydrochloride. The shift in maximum wavelength indicates loss of tryptophan asymmetry, but less so of tyrosine. (B) Seed coat soybean peroxidase under native and denaturing conditions (data from Kamal and Behere, 2002). Protein concentration 15 pM and path length 10 mm. The negative aromatic band centered around 280 nm and the Soret band around 410 nm both disappear at 90°C, indicating the loss of net conformational asymmetry of the aromatic and heme chromophores.

Edible Products Derived from Soybean Meal. The primary edible products derived from soybean meal/flakes are flour/grits (at 50% protein), protein concentrates (containing 65-70% or more of protein) and protein isolates (90% protein). The nutritional quality, availability, price, and functionahty of these products has resulted in substantial usage in a wide variety of food and feed products. Given current trends in food consumption, strong growth in the use of soy protein products in foods appears assured (8, 9). A number of excellent articles on the manufacture of soy protein products exist processing will not be described in detail here (8, 10-13). 

Eldridge (1982a,b) reported analysis of soybean and soy products using HPLC with an external standard method. They found 80% ethanol extraction for 4 hr was suitable for extraction of isoflavones from soybean, soy protein concentrate and protein isolate. They also found that daidzin and genistin accounted for 50-75% of the total isoflavones. Eldridge and Kwolek (1983) reported analysis using selected external standards and n-butyrophenone as an internal standard. 

Fig. 3. Left EPR spectra of membrane-bound iron-sulfur proteins reduced by dithionite and methyl viologen. HP700 particles from spinach (A), soybean (B) and Anabaena chloroplasts (C). Spectra D and E are for chloroplasts prepared from mutant No. 8 of Scenedesmus obliquus and for TSF-IIa particles, respectively. Right plot of the EPR-signal amplitude at g=2.05 due to reduced iron-sulfur-protein vs. the P700 concentration in chloroplast and subchloroplast samples from various sources (1, unfractionated chloroplasts 2, D144 particles 3, TSF-1 particles 4. D144 from stroma 5, D144 from grana 6, HP700 particles 7, HP700 particles from soybean 8, chloroplasts from Anabaena 9, chloroplasts from mutant No. 8 of Scenedesmus obliquus-, and 10, TSF-2a particles. Unpublished results of B Ke and H Beinert (1973).

Solubilization of Protein. Fish protein concentrate has high nutritional quality as determined both from its essential amino acid composition and from animal feeding experiments. Unfortunately, the concentrate is quite insoluble in water because of its denaturation by the solvent extraction method used in processing thus it contributes no functional properties to a food and must be used in bakery products primarily. A potentially useful method of solubilizing the protein is by proteolysis (9-12). As is the case with protein hydrolysates of casein and soybean protein, bitter peptides are formed during the hydrolysis. Papain and ficin produce more of these bitter peptides than does Pronase, for example (12). Pronase was found to produce a more brothy taste (13). A possible method of removing the bitter peptides is to convert the concentrated protein hydrolysate to plastein by further proteolytic enzyme action (14) to remove the bitter peptides. 

Partial proteolysis of soybean proteins with endopeptidases has been used to remove flavor compounds and related fatty materials from soybean curd and defatted soybean flour (21). Certain soybean protein concentrates possess an undesirable beany and oxidized flavor. Treatment of soybean curd and defatted soybean flour with endopeptidases such as aspergillopeptidase A released off-flavor compounds such as 1-hexanal and 1-hexanol which could be removed from the hydrolysate by solvent extraction. The enzymically digested products had less odor, taste, and color than the starting material and were more stable to oxidative deterioration. 

In soybean concentrates and isolates much of the phytate remains associated with the protein in fact, phytate may constitute as much as 2-3% of the weight of a commercial protein isolate (57). A low-phytate soybean protein isolate can be prepared from soybean flour, however, by allowing endogenous phytase to act on the phytate in a 6% suspension of the flour at pH 5 at a temperature of 65°C (58). Hydrolysis of the phytate facilitates its separation from the bulk of the soybean protein which is then concentrated by ultrafiltration using a membrane which is permeable to phytate and its hydrolysis products but impermeable to protein. The product obtained by this method contains over 90% protein and only about 0.3% phosphorus. 

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