Soy protein preparation

Not all studies of soy protein diets in humans have found significant reduction of plasma cholesterol. In addition to differences in diet formulations and soy protein preparations, one reason that has been proposed for these disparities is that there is a statistically significant negative correlation between the initial cholesterol level and the decrease of cholesterol achieved with the soy protein diet (r -0.48, p < 0.01) (23). In other words, those with normal or slightly elevated cholesterol levels would be expected to show less change in cholesterol as a result of the soy diet than individuals with markedly elevated lipids. Sirtori and associates (23) have followed a number of type II hyperlipoproteinemic patients who have been maintained on the soy... 

Setchell, K.D., Welsh, M.B., and Lim, C.K. (1987). High-performance liquid chromatographic analysis of phytoestrogens in soy protein preparations with ultraviolet, electrochemical and thermospray mass spectrometric detection, J. Chromatogr., Jan, 16, 386, 315-323. 

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 (9) soy protein concentrate (/ ) soy flour (defatted) fCJl carbohydrate-enriched fraction of soy concentrate f32j.

Soy protein preparations contain a variety of biologically active compounds including saponins, fibers, trypsin inhibitors, and isoflavones (Potter, 2000). Hamsters and rats fed ethanol-extracted soy protein isolates had no ability to lower plasma cholesterol compared to intact soy protein isolates (Lucas et al., 2001 Ni et al., 1999). Extraction with ethanol is a treatment that would remove saponins, isoflavones, and other phytochemicals from the protein. Although one study showed that ethanol washing did not... 

Barbuch, R. X Coutant, X E. Welsh, M. B. Setchell, K. D. 1989. The use of thermospray liquid chromatography/tandem mass spectrometry for the class identification and structural verification of phytoestrogens in soy protein preparations. Biomed. Environ. Mass Spectrom., 18, 973-977. 

Commercial soy protein concentrates typically contain 70 to 72% cmde protein, ie, nitrogen x 6.25, dry wt basis. Soy protein isolates are prepared from desolventhed, defatted flakes. A three-stage aqueous countercurrent extraction at pH 8.5 is used to disperse proteins and dissolve water-soluble constituents. Centrifugation then removes the extracted flakes, and the protein is precipitated from the aqueous phase by acidifying with HCl at pH 4.5. 

Products prepared from soy protein products and resembling chicken, ham, frankfurters, and bacon are available commercially. Soy protein isolates are used in place of milk proteins or sodium caseinate in products such as coffee creamers, whipped toppings, yogurt, and infant formulas (see Dairy substitutes). Soy protein products also are used in snacks and in baked foods. 

Pish protein concentrate and soy protein concentrate have been used to prepare a low phenylalanine, high tyrosine peptide for use with phenylketonuria patients (150). The process includes pepsin hydrolysis at pH 1.5 ptonase hydrolysis at pH 6.5 to Hberate aromatic amino acids gel filtration on Sephadex G-15 to remove aromatic amino acids incubation with papain and ethyl esters of L-tyrosine and L-tryptophan, ie, plastein synthesis and ultrafiltration (qv). The plastein has a bland taste and odor and does not contain free amino acids. Yields of 69.3 and 60.9% from PPG and soy protein concentrate, respectively, have been attained. 

The sulfur amino acid content of soy protein can be enhanced by preparing plasteins from soy protein hydrolysate and sources of methionine or cystine, such as ovalbumin hydrolysate (plastein AB), wool keratin hydrolysate (plastein AC), or L-methionine ethyl ester [3082-77-7] (alkaU saponified plastein) (153). Typical PER values for a 1 2 mixture of plastein AC and soybean, and a 1 3 mixture of alkah-saponified plastein and soybean protein, were 2.86 and 3.38, respectively, as compared with 1.28 for the soy protein hydrolysate and 2.40 for casein. 

The in vitro digest was prepared by digesting a soy protein isolate. For each UF determination, 50 ml of the 100,000 g supernatant was introduced into the UF chamber. Values are mean S.D. for four experiments. 

Calculation of Brine Components. In order to satisfy U.S.D.A. regulations, care must be taken during brine preparation so that finished product protein meets or exceeds 17 percent. The following formula can be used to determine brine composition (Isolated soy protein, salt, dextrose, polyphosphate, etc.) (6). 

Among the vitamin K vitamers, only phylloquinone is accounted for routine food analysis. Furthermore infant formulas, both milk-based and soy protein-based, are supplemented with a synthetic preparation of phylloquinone (the only form admitted) [403], which usually contain about 10% of the biologically inactive ctT-isomer [497]. 

An important caveat is that the epidemiological evidence suggesting protection from hormone-dependent cancer by isoflavone phytoestrogens is based on foods rather than isoflavone extracts, which in the future could include isoflavone-containing therapeutics. Indeed, the preparation of isoflavone extracts from soy protein could well result in the loss... 

Preparation of Modified Soy Proteins from Germinating Soybeans. Soybean seeds (12 g dry weight) were germinated on wet Vermiculite in a metal pan covered with aluminum foil. Water was added to the tray as needed during the course of germination. To collect products, the germinated seeds were washed and then ground with mortar... 

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