Production of value-added peptides from soybean meal during natural solid-state fermentation: Metabolites and bacterial communities

This study is aimed at producing value-added peptide products from soybean meal (SBM) through natural solid-state fermentation (NSSF) using the indigenous microorganisms present in SBM. The variation of metabolites and the succession of bacterial communities in SBM fermentation were explored. Results revealed that during NSSF, the pH, microbial counts, the contents of soluble protein, peptide, and free amino acids (FAAs), and protease activity increased (p < 0.05), whereas the trypsin inhibitor (TI) activity decreased significantly (p < 0.05) under optimal NSSF conditions (ambient temperature of 45 °C and moisture content of 55%). Molecular weight (MW) distribution showed that macromolecular proteins in the SBM were degraded into small peptide fragments with MW < 3000 Da after NSSF. Bacillus and Bacillus subtilis were the predominant bacterial genera and species, respectively, in the NSSF process, which was highly associated with the accumulation of metabolites, including soluble protein, peptide, and protease, and the degradation of TI. NSSF could be regarded as an effective way to enhance the nutritional value and produce value-added peptides from the SBM.