Preparation and Characterization of Peptides from Rana chensinensis skin via Microbial Fermentation

As the main by-product of Rana chensinensis product processing, Rana chensinensis skin has important development and utilization value because it is rich in a variety of bioactive components. In this study, Bacillus subtilis was used as the fermentation strain to explore the efficient preparation process and antioxidant activity of peptides from Rana chensinensis skin. The fermentation conditions were optimized by single factor experiment and response surface analysis, and the optimal parameters were determined as follows: inoculum volume was 3%, fermentation time was 16 h, and shaking speed was 190 rpm. Under these conditions, the peptide content of the fermentation product reached 71.46 ± 0.92 mg/mL, and the DPPH scavenging rate was 81.29 ± 1.03%, which were 1.77-fold and 4.71-fold higher than those before fermentation, respectively, and the antioxidant activity was significantly improved. The molecular weight distribution of peptides in fermentation liquor was further analyzed by high performance liquid chromatography. The results showed that the proportion of peptides with molecular weight less than 10,000 Da was up to 90%, and 50.54% of small peptides were concentrated in the range of less than 3000 Da. Subsequently, small molecular peptides were obtained by ultrafiltration centrifugation, which showed higher DPPH scavenging rate, and their key role in antioxidant activity was verified. This study realized the high-value utilization of Rana chensinensis skin, not only laid an experimental foundation for its application in various fields, but also provided a scientific basis for the sustainable utilization of Rana chensinensis skin.