Application of ultrasound technology in the field of solid‐state fermentation: increasing peptide yield through ultrasound‐treated bacterial strain

Abstract BACKGROUND The increase of peptide yield contributed to reducing the usage of antibiotics in solid‐state fermented feed. Ultrasound technology is used in the field of liquid‐state fermentation to improve yield of fermented products but has not been utilized in the field of solid‐state fermentation (SSF). The main objective of this study was to investigate the feasibility of improving peptide yield in SSF products through ultrasound‐treated bacterial strain. RESULTS The highest peptides content in soybean meal SSF products reached 153.28 mg g −1 , which increased by 15.05% compared with the control. This content value was acquired through treating the bacteria of Bacillus amyloliquefaciens by ultrasound before inoculating into soybean meal under the optimized mode and parameters (simultaneous dual‐frequency ultrasound mode, frequency combination of 40/60 kHz, total power density of 40 W L −1 , time of 20 min, pulse‐on and pulse‐off times of 40 and 60 s, delayed inoculation time of 0 h). Fermenting with ultrasound‐treated bacterial strain can effectively increase peptide yield, biomass and protease activity of soybean meal fermented products during the SSF prophase. After treating by ultrasound, the latent phase and logarithmic phase of the bacterial strain shortened by 1 and 3 h while the generation time reduced by 23.64%. In qualitative test of protease activity, diameter ratio (DR) value of ultrasound‐treated bacterial cells enlarged by 12.0% compared with the control. CONCLUSION Peptide yield of soybean meal SSF products can be improved through ultrasound‐treated bacterial inoculum, which attributed to the promoting effect of ultrasound treatment on growth activity and protease production capability of bacterial cells. © 2021 Society of Chemical Industry