Combined uses of an endo- and exopeptidase in okara improve the hydrolysates via formation of aglycone isoflavones and antioxidant capacity

The aim of the study was to apply Alcalase and Flavourzyme proteases and their combinations in okara to produce protein hydrolysates and obtain hydrolyzed protein with higher antioxidant capacity and content of isoflavone aglycones. Several Alcalase and Flavourzyme combinations were used. The hydrolysis process was evaluated by the degree of hydrolysis and recovery of proteins. Protein hydrolysates were characterized by antioxidant capacity measures, isoflavone content, the amino acid profile, and molecular weight. After the hydrolysis, the protein bands in the electrophoresis were less intense, more diffuse, and their molecular weight was below 14.4 kDa. Hydrolysis with Alcalase increased the antioxidant capacity from 36.0 to 202.1, 7.3 to 20.3, and 1.2-5.9 mu mol Trolox/g of solids according to the ABTS, FRAP, and DPPH assays, respectively. Protein hydrolysates produced by Flavourzyme followed by addition of Alcalase had higher isoflavone aglycones content. The permeate fractions 3-10 kDa and > 30 kDa of hydrolysates produced by Alcalase had higher antioxidant capacity than did the fraction < 3 kDa. Therefore, it was possible to obtain protein hydrolysates of nutritional quality by applying different protease combinations to the coproduct generated by the soymilk industry.