Soybean proteins solubility

Cyclic adenosine monophosphate-dependent protein kinase is useful for phosphorylation of a.a. residues in mild conditions. The modification makes the soybean proteins soluble in media rich in calcium and improves their emulsifying properties (Seguro and Motoki, 1990). 

Glimp, ff.A. M.R. Karr C.O. Little P.G. Woolfolk G.E. Mitchell, Jr. L.W. ffudson. Effect of reducing soybean protein solubility by dry heat on the protein utilization of young lambs./. Anim. Sci. 1967,26, 858-865. 

Parsons, C.M K. Hashimoto K.J. Wedekind D.H. Baker. Soybean protein solubility in potassium hydroxide An in vitro test of in vivo protein quality. /. Anim. Sci. 1991, 69, 2918-2924. 

In limited proteolysis, proteases such as pronase E hydrolyzed the 7S subunits of soy proteins more than the IIS subunits, resulting in enhanced protein solubility. Deamidation with relatively insignificant peptide bond hydrolysis that occurred during the germination of soybeans imparted to the storage protein improved solubility and emulsifying activity. On the other hand, the incorporation of phosphorus in soy proteins by the protein kinase cAMPdPK was too low to effect significant... 

Foam properties related to salt. The addition of sodium chloride to soybean protein suspensions caused them to form high-capacity, low-stability foams (13). It was suggested that foam capacity increased because salt improved protein solubility at the interface of the colloidal suspension during foam formation, but retarded the partial denaturation of the surface polypeptides of proteins that are necessary for protein-protein interaction and stability. 

Figure 14. Foam capacity and protein solubility properties of defatted soybean, peanut, field pea, and pecan seed flour suspensions at various pH values (4T)...

Observations made in this study indicate that protein solubility was more closely related to the type of foam produced than to increase in capacity. For example, soybean and peanut seed flour suspensions contained higher levels of soluble protein than field pea and pecan suspensions and produced foams of much thicker consistency and smaller air cells. 

Zu, S., Riaz, M. N., and Lusas, E. W., Effect of different extrusion temperatures and moisture content on lipoxygenase inactivation and protein solubility in Soybeans, J. Agric. Fd. Chem., 44,3315-3318 (1996). 

The ash content of soybeans is relatively high, close to 5 percent. The ash and major mineral levels in soybeans are listed in Table 5-7. Potassium and phosphorus are the elements present in greatest abundance. About 70 to 80 percent of the phosphorus in soybeans is present in the form of phytic acid, the phosphoric acid ester of inositol (Figure 5-5). Phytin is the calcium-magnesium-potassium salt of inositol hexaphosphoric acid or phytic acid. The phytates are important because of their effect on protein solubility and because they may interfere with absorption of calcium from the diet. Phytic acid is present in many foods of plant origin. 

Figure 6. The insolubitization of soybean protein during frozen storage at —5°C and their solubility behavior in urea and mercaptoethanol (ME) (10).

Figure 8. The insolubilization of soybean protein during storage at +5°C in a concentrated state and its solubility behavior in urea ana mercaptoethanol (ME)...

Free -SH groups are also very sensitive to oxidation even by air. Native soybean protein in solution became less soluble when frozen immediately after preparation than it did when frozen after storage for 2 days (Fig. 13). The same behavior was found for heated soybean protein frozen immediately or after two days. 

Lin et al. (15) showed that sunflower meal was superior to soybean and sunflower concentrates or isolates In emulsion capacity. McWatters and Cherry (9) compared select functional properties of defatted soybean, peanut, field pea, and pecan flours and showed that major seed storage proteins were important in emulsifying and foaming properties. Protein solubility was related to the quality of the emulsions and foams. Behavioral characteristics contributed by nonprotein components that occur naturally In the seeds, especially carbohydrates, were Implicated. 

Recently, a study was made of the electrophoretic as well as other physical and chemical properties of three types of soybean protein fractions (19). It was found that heating generally reduced the solubility of a suspension of these fractions and also increased their viscosity. These changes were attributed to subunit dissociation and aggregation. 

Laboratory tests such as urease activity, protein dispersibility index (PDI), nitrogen solubility index (NSI), thiamine, and water absorption have been found valuable in monitoring daily production for protein quality. But biological chick and/or rat assays are the only reliable means currently available for predetermining the nutritional value of whole soybean protein they must be conducted periodically to verify results of chemical tests (31). If whole soybeans are to be used in a mixture containing 20% or more soybean meal, 5% or more urea, and 20% or more molasses, or an equivalent mixture, and exposed to hot, humid storage conditions, it is advisable that the urease activity of the whole soybeans not exceed 0.12 increase in pH (31). Extruded or roasted soybeans properly treated for cattle to increase bypass protein should have urease values of less than 0.05 pH rise. A urease rise of 0.05-0.20 is an indication of proper treatment for swine and poultry. 

FIGURE 21.14 Effect of acidification procedure on the percentage of soluble proteins measured during pH decrease of electrochemical and chemical acidification of soybean protein solution, with 0.06 M KCl and maintained at 25°C. (Adapted from Bazinet, L., Lamarche, F., and Ippersiel, D., J. Agric. Food Chem., 46, 2013, 1998.)... 

Alkalies and Acids. The older literature dealing with the treatment of soybean proteins with alkaline substances is quite extensive since these agents have often been used for protein extraction, solubilization, and property modification, including improved solubility, increased adhesive properties, and lower viscosity in dispersion and fiber formation (12, 21, 23, 24). The alkali treatment of soy protein for industrial use is done under conditions which are more severe (higher temperature and higher pH, such as possibly 50 °C at pH >13) than those intended for food usage. 

Improvement of Solubility of Soybean Protein. Denatured soybean protein is relatively insoluble in aqueous media, which is a disadvantage in processing this protein. This problem might be solved by incorporating a large amount of certain hydrophilic amino acid into soybean protein through its enzymatic degradation and resynthesis. Yamashita et al. (73,... 

The protein solubility test (KOH) or nitrogen solubility index (NSI) is an indicator of solubility of protein in an alkaline solution of potassium hydroxide (KOH). It indicates the percentage of total nitrogen (protein) that is soluble. Protein solubility is important for tofii and soymilk production and for estimating the level of toasting or damage in soybean meal. Soybean meal should have a protein solubility index when... 

Wang and Johnson (2001) reported on test measurement methods that were major indicators of soybean oil quality. These tests included peroxide value, anisidine value, FFA content, phospholipid content, total tocopherol content, oxidative stability index, color, and moisture content. For soybean meal, they reported on urease activity, protein dispersibility index (PDI), rumen bypass or rumen undegradable protein, trypsin inhibitor activity, moisture content, residual oil content, protein content, fiber content, color, amino acid profiles, and protein solubility under alkaline (KOH) conditions. 

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