Optimization of the Fermentation Conditions for Producing Antioxidant Peptides From Yak (Bos grunniens) Casein by Bacillus cereus (XBMU-SK-01)

Antioxidant peptides could interact with free radicals and excess reactive oxygen species to avoid the organism from oxidative harm; at the same time, antioxidant peptides have the characteristics of high safety, good stability, and wide application. In this study, a strain named XBMU-SK-01 with high proteinase activity was isolated and identified from fermented bean curd. The results showed that the strain (XBMU-SK-01) with protease activity of 96.2 ± 1.3 U/mL was identified as Bacillus cereus based on 16S rDNA gene sequencing. The yak casein antioxidant peptide was prepared through fermentation using Bacillus cereus (XBMU-SK-01), and the fermentation conditions were optimized by response surface methodology (RSM) based on the Box–Behnken design, using 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) radical scavenging rate and the degree of hydrolysis (DH) as indicators. It was found that the optimal fermentation conditions for the preparation of antioxidant peptides from yak casein by Bacillus cereus (XBMU-SK-01) were as follows: pH of 7.96, temperature of 32.5°C, and inoculation amount of 6.99%. Under these conditions, the DPPH free radical scavenging rate could reach 78.19% ± 0.21%, and DH is 19.8% ± 0.15%. Following the sequence analysis of antioxidant peptides, 11 distinct polypeptide sequences were identified: FPP, AFK, GILF, PAAP, VIGP, TIPT, IEQI, FPFF, IPLLP, KPWIQP, and EAGPPGP. This study is aimed at establishing a preparation pathway for peptides with high antioxidant activity and proposes a novel method for producing high-value products from yak milk.