Screening of High Yielding Antioxidant Peptide Bacillus sphaericus and Its Application in Value-added Utilization of Soybean Residue

Objective: Soybean dregs, a major by-product of soybean processing, possess nutritional value but have low industrial utilization due to low digestibility and poor palatability. The aim of this study was to use soybean dregs as a fermentation substrate, take advantage of the characteristics of Bacillus sp. that can grow and multiply in food materials and secrete an extracellular enzyme system, and explore an effective way to prepare small molecule bioactives such as antioxidant peptides with the help of ultrasonic-combined microbial fermentation (UAF), thereby enhancing the utilization value of soybean dregs. Methods: In this study, 28 high-protease-producing strains were screened from 56 strains of Bacillus sp. by initial screening using the transparent-circle method. Then, their protease activity, superoxide dismutase activity, peptide-producing capacity, and antioxidant capacity were comprehensively evaluated through re-screening in combination with factor analysis. Results: Four strains with antioxidant capacity, namely B. siamensis S4, B. amyloliquefaciens 10, B. subtilis SNBS-3, and B. subtilis 63, were finally screened out. Among them, the protease activity, ABTS⁺ radical scavenging rate, and DPPH radical scavenging rate of B. amyloliquefaciens 10 were significantly increased （P<0.05）to 12.23%±0.08%, 8.69%±0.11%, and 3.38%±0.81%, respectively. Meanwhile, the peptide content and DPPH radical scavenging rate of B. subtilis SNBS-3 were significantly increased （P<0.05）to 7.20%±0.10%, 3.41%±0.14%, respectively. Conclusion:Using soybean dregs as a fermentation substrate, ultrasonication combined with microbial fermentation can be regarded as a method to screen strains with high antioxidant peptide production. Under ultrasonication stress conditions, the two strains, B. amyloliquefaciens 10 and B. subtilis SNBS-3, not only demonstrated good growth ability but also significantly enhanced protease activity, peptide content, and antioxidant capacity. They have strong antioxidant potential and provide theoretical support for the industrialization of antioxidant peptide preparation.