Soybean protein isolate hydrolysate addition during fermentation of soybean meal with Aspergillus oryzae enhances the release of umami components in subsequent hydrolysis process

This research aimed to develop umami enhancers through solid-state fermentation of soybean meal with Aspergillus oryzae then enzymatic hydrolysis. The enzymatic hydrolysate of fermented soybean meal possessed significant umami taste and umami-enhancing capacity. Addition of soybean protein isolate hydrolysate (SPIH) before fermentation enhanced the fermentation system's neutral protease, alkaline protease, acidic protease, aminopeptidase and glutaminase activities, increased the release of umami-active peptides/amino acids, thereby enhancing the umami intensity and umami-enhancing capacity of the final hydrolysate of fermented soybean meal (FSHE). The peptide Asp, peptide Glu, ME, EV, EA, and EA of FSHE showed improvements of 10.0 %, 6.6 %, 54.5 %, 75.2 %, 232.0 %, and 17.5 %, respectively, compared to the SPIH-free final hydrolysate of fermented soybean meal (FSHC). The critical stage for generating umami components in FSHE was the first 8 h of enzymatic hydrolysis, and SPIH mainly affected the release of umami components during this period. The peptides smaller than 1000 Da and peptide sized 1000–3000 Da in the FSHE accounted mainly for rapid increase of FSHE's umami intensity and umami-enhancing capacity during the first 8 and 12 h of enzymatic hydrolysis, respectively. FSHE's umami characteristics were influenced by free amino acids (Glu and Asp), peptide amino acids (Glu and Asp), and umami-enhancing peptides (ME, EL, EA and EV). Besides neutral protease, alkaline protease and acidic protease, aminopeptidase and glutaminase from Aspergillus oryzae were also the key contributing enzymes to the production of umami components in FSHE.