Microbial hydrolysis of Camellia seed cake with Bacillus subtilis: Fermentation process optimization and bioactivity assessment of the hydrolysates

The Camellia seed cake (CSC) is by-product of tea tree ( Camellia oleifera ) oil that rich in proteins and traditionally discarded or used as fertilizers, which would lead to a serious waste of the high-quality resources. In this work, Bacillus subtilis was employed to the submerged fermentation of CSC for production of potential bioactive peptides. After optimization by single-factor experiments and response surface methodology (RSM), the optimal fermentation conditions revealed to be material-to-liquid ratio of 30 g/L, inoculum volume of 19.0 %, and temperature of 35.4 °C, and the peptide production yield reached 11.68 % after RSM optimization. The amino acid composition analysis of CSC hydrolysates (CSCH) showed that CSCH was mainly composed of Tyr, Cys, Gly and Val, and 94.01 % of the peptides contained in the CSCH had a molecular weight of less than 3 kDa. In addition, the CSCH revealed strong antioxidant and tyrosinase inhibition potential in vitro, and the Lineweaver–Burk analysis indicated that CSCH exhibited a reversible competitive inhibition against the tyrosinase. Peptides were supposed to be major components that contribute to the bioactivity of CSCH due to their high contained concentration. The results demonstrated that CSCH could be developed as a new type of pure natural antioxidant and anti-tyrosinase agents used for health-promoting products, and these findings would provide useful information for better transformation and utilization of the CSC by-products.