Simulated natural and high temperature solid-state fermentation of soybean meal: A comparative study regarding microorganisms, functional properties and structural characteristics

A comparative study regarding microorganisms, functional properties and structural characteristics of soybean meal (SBM) was explored after simulated natural fermentation (SNF) by Bacillus subtilis 21927 and high temperature fermentation (HTF) by Bacillus subtilis 22983. The results showed that SNF inhibited the growth of molds and coliforms effectively by their own heat production, which was comparable to HTF. Both SNF and HTF increased peptide content and decreased trypsin inhibition significantly. In vitro antioxidant activity, ACE inhibitory activity and emulsifying activity and stability of fermented SBM were found to be noticeably improved in SNF process (p < 0.05). After SNF and HTF, the total amino acid of SBM in substrate increased by 16.13% and 12.91%, and the essential amino acids increased by 16.01% and 16.50%, respectively. SDS-PAGE revealed that anti-nutritional factors were significantly degraded into small molecular protein or peptide and further degraded to complete in SNF process. Besides, particle size and Zeta potential also indicated that SNF markedly hydrolyzed SBM protein more thoroughly compared with HTF. Collectively, SNF by B. subtilis 21927 reduced miscellaneous bacteria pollution and improved nutrition and structure of SBM better than HTF by B. subtilis 22983, providing certain guiding significance for the SBM fermentation industry.