Solid-state fermentation of black rice bran with Aspergillus awamori and Aspergillus oryzae: Effects on phenolic acid composition and antioxidant activity of bran extracts

Abstract

Black rice bran (BRB) was fermented in solid state using Aspergillus awamori and Aspergillus oryzae for 5 days at 30°C, and then the alcoholic extracts of the fermented BRB were examined in terms of phenolic acid composition and antioxidant activity (DPPH radical scavenging and tyrosinase inhibitory activity). A pre-treatment, moisturizing and autoclaving prior to the fermentation, decreased total phenolic content (TPC) by decomposing the anthocyanin in BRB, but the fermentation increased TPC. Protocatechuic acid and ferulic acid showed the most significant increases, reaching their maximum values by the fermentation for 3 days: 1660.6 µg/g for the extract of BRB fermented by A. awamori. The radical scavenging activity and tyrosinase inhibitory activity of the alcoholic extracts increased by the pre-treatment and fermentation, in accordance with the increase in phenolic acid content. The solid-state fermentation was an effective process to raise the phenolic acid content and antioxidant activity of the extract.

Keywords: Antioxidant activity; Aspergillus fungi; Black rice bran; Phenolic acid; Solid-state fermentation.