Effects of solid-state fermentation and proteolytic hydrolysis on defatted soybean meal

This study explored the optimized combination of solid-state fermentation (with Aspergillus oryzae) and proteolysis processes upon koji and hydrolysate properties to overcome the limitations of defatted soybean meal (DSM) in food applications. After 44 h fermentation, no change in total nitrogen content (dry basis), a decreased weight (34.5% moisture loss) and total sugar (40.91% loss on dry basis), and an elevated total acid before a plateau (2.75%) at 20 h were observed. A significant decrease of > 10 KDa peptides in the aqueous extract of koji, and the neutral protease activity increased gradually with fermentation time (720,13-1743.55 U/g corresponding 16-40 h). The hydrolysates obtained via fermentation (different times) before proteolysis (34 h) differed in protein recovery, degree of hydrolysis and antioxidant activities with the one (24 h fermentation) having the highest values. The hydrolysates obtained via fermentation (24 h) coupled proteolysis (different times) differed in taste qualities and molecular weight of which the one (with 22 h hydrolysis) have the best taste and 78% peptide fractions < 3 KDa. Thus, the hydrolysis efficiency of koji was irrelevant to its neutral protease activity. Solid-state fermentation and proteolysis are useful technologies for utilizing DSM for food applications.