Production of value-added peptides from agro-industrial residues by solid-state fermentation with a new thermophilic protease-producing strain

This work aimed to explore an effective way for converting agro-industrial residues into value-added products. A thermophilic protease-producing strain was isolated from soybean meal (SBM) and identified as Bacillus licheniformis by 16S rDNA sequencing. After incubating Bacillus licheniformis CPB2 in casein medium for 24 h, the protease activity, peptide yield, and protein conversion rate of the culture could reach 8.87 ± 0.33 U/mL, 68.58%, and 82.27%, respectively. Brewer's spent grain (BSG) and SBM were used as co-substrates to produce value-added peptides through thermophilic solid-state fermentation (TSSF) with Bacillus licheniformis CPB2 . The peptide content of the co-substrates increased from 25.71 mg/g to 112.72 mg/g under the optimal TSSF conditions. The fermented products showed an increased crude protein and free amino acids contents and a decreased crude fat and ash contents as well as trypsin inhibitor activity compared with the unfermented co-substrates. TSSF could degrade macromolecular proteins into peptides, unfold the protein aggregates, and reduce the particle size. Industrial relevance This work proposed an effective way for the rational and efficient utilization of wet and dry agro-industrial residues to produce value-added products, which showed a broad potential for reducing production costs, saving water resources and energy, and preserving the ecological environment.