Changes in the native state and functional properties of soy protein achieved by limited proteolysis of soy flour were investigated. Different enzyme-to-substrate ratios (E/S) were used to obtain low (3-5%) and medium (5-10%) degrees of hydrolysis (DH). Six protease preparations (three with predominately exopeptidase activities and three with predominately endopeptidase activities) were evaluated, and their effects on solubility, emulsification capacity, SDS-PAGE profiles, and denaturation enthalpies were characterized. Endoproteases (Multifect ® Neutral, Protex™ 6L, and Multifect ® P-3000) and exoproteases (Fungal Protease Concentrate, Experimental Fungal Protease #1, and Experimental Fungal Protease #2) yielded similar increases in soy protein solubility. The modifications to the soy peptide profile were similar for the three exoprotease mixtures at a 1% E/S ratio, whereas the extent of hydrolysis with Protex™ 6L was more pronounced than with the two other endoproteases (Multifect ® Neutral and Multifect ® P-3000). The emulsification capacity of protease-modified soy flour declined regardless of DH and enzyme type (exo-or endoprotease). After hydrolysis to >4% DH, denaturation enthalpies of glycinin and β-conglycinin decreased significantly, whereas hydrolysis to lower DH did not affect these values. FIG. 1. Degree of hydrolysis (DH) as a function of time for various enzyme-to-substrate (E/S) ratios using (A) Fungal Protease Concentrate and (B) Protex™ 6L. The curves represent the averages of two replications.
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