Effect of fermentation by Bacillus subtilis on antioxidant and cytotoxic activities of black rice bran

Summary Black rice bran was fermented with Bacillus subtilis KU3 isolated from Korean traditional food, Kimchi. Antioxidant and cytotoxic activities of the fermented black rice bran were investigated. Total phenolic and anthocyanin contents decreased from 171.54 mg GAE g−1 and 2.31 mg g−1 to 139.13 mg GAE g−1 and 2.12 mg g−1, respectively, after fermentation. Antioxidant activities determined by 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical scavenging, β‐carotene bleaching and ferric thiocyanate assay were correlated with total phenolic and anthocyanin contents. Non‐fermented black rice bran extract (NFBE) showed greater antioxidant activities than fermented black rice bran extract (FBE). Cytotoxic activities measured by MTT assay showed that both NFBE and FBE had over 50% activities. The cytotoxic activities of FBE against MCF‐7 and HeLa cells were 71.65% and 68.07%, respectively, at 8.0 mg mL−1, but those of NFBE were lower than 50%. These results suggested that the cytotoxic activity of black rice bran improved through fermentation, while antioxidant activity reduced. Fermentation of black rice bran by Bacillus subtilis isolated from Kimchi impacted to decrease antioxidant activities and improve cytotoxic activities.