Study On Preparation Of Modified Soy Protein By Enzymatic Hydrolysis-Membrane Separation

Modified soy protein concentrates (EMSPs) were prepared by selective enzymolysis-ultrafiltration of soy protein aqueous extracts from defatted soy flour. The simple and viable schematic process, succeeding in enzymatic hydrolysis, separation and concentration, gave a new way for comprehensive utilization of defatted soy flour to improving its added value.Five proteases were used to hydrolyze the native soy protein in the study. It was proved by SDS-PAGE that the native protein could be hydrolyzed selectively by protease. Generally, β-conglycinin was hydrolyzed more easily than glycinin, α' or α subunits of β-conglycinin were more sensitive to hydrolysis than β subunit, acid subunit of glycinin was more sensitive to hydrolysis than its basic subunit.The aqueous extracts of soy protein (SP), obtained by centrifugation from the defatted soy flour suspension in water at pH 8.0 after continuous agitation for 40 min at ambient temperature, was selectively hydrolyzed by proteases, and then subjected to ultrafiltration membrane for fractionation. After inactivation of enzyme, the retentate was lyophilized to yield the desired products at the protein yield of over 80% and protein content more than 75%. The fouled membrane was cleaned commendably by water rinsing and chemical reagents cleaning, the water flux recovery was more than 90%.SDS-PAGE pattern showed that modified soy proteins by selective enzymolysis-ultrafiltration mainly contained acid and basic subunits of glycinin. The results of the analysis of amino acid profile revealed that EMSPs had similar amino acid patterns, however they had different amino acid patterns from the defatted soy flour and acid precipitation soy protein (APP). The EMSPs had relatively higher levels of glutamic acid/glutamine in comparison to defatted soy flour and APP but slightly lower levels of aspartic, arginine and leucine. In comparison with APP, the surface hydrophobicity of EMSPs increased markedly.There were lots of deference between functional properties of EMSPs and those of APP. Comparison with APP, the solubility of EMSPs increased, especially increased evidently at pH 4.0-8.0; the emulsion activity index of EMSPs improved, emulsion stability index of EMSPs were no more change; foaming capacity of EMSPs increased, however foaming stability of EMSPs decreased; holding water capacity of...