Feasibility study on direct fermentation of soybean meal by Bacillus stearothermophilus under non‐sterile conditions

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BACKGROUND: To evaluate the feasibility of high-temperature solid-state fermentation (SSF) using soybean meal (SBM) during the non-sterile process, Bacillus stearothermophilus was employed to assess the nutritional quality and bioactivity of SBM after fermentation. RESULTS: The fermented SBM (FSBM) without autoclaving showed significant improvements in nutritional quality and bioactivity. The contents of peptides and crude and soluble proteins increased by 131.21%, 5.3% and 15.52%, respectively. Meanwhile, DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging ability, reducing ability and hydroxyl free radical-scavenging activity rose by 57.07%, 238.92% and 368.26%, respectively. The inhibitory activity of angiotensin I-converting enzyme increased from 1.43 ± 0.83% to 26.89 ± 1.03%, while the trypsin inhibitor activity decreased by 74.05%. The contents of neutral and alkaline proteases and the growth of microorganisms in FSBM without autoclaving were higher and better than in steam-treated FSBM. After steam treatment, the water-holding capacity of SBM decreased, and a high crosslink density was observed on the surface of SBM particles. CONCLUSIONS: It is feasible to ferment SBM by high-temperature SSF using B. stearothermophilus under non-sterile conditions. Adverse effects of SSF using sterile SBM might be owing to the low water-holding capacity caused by autoclaving.