Quantification of phenolic compounds changes by Aspergillus oryzae on rice bran fermentation

Abstract

This research highlights the quantification of phenolic compounds of rice by-products (namely rice bran), by solid-state fermentation (SSF) with Aspergillus oryzae through assessment of its total phenolic content (TPC) and phenolic acids. The analyses were carried out by comparing fermented extracts of rice bran extracted using water extract according to their fermentation time and uninoculated samples. Alpha-amylase and beta-glucosidase assays were used to identify the differences in their expression levels during fermentation. The results show that fermentation with A. oryzae improved the extractable TPC of rice bran by up to 3.8-fold higher in comparison to its unfermented counterpart. A total of three types of phenolic acids (protocatechuic, coumaric and ferulic acids) were detected in unfermented rice bran by HPLC/PDA. SSF with A. oryzae on rice bran significantly influenced the free phenolic content i.e. the five phenolic acids p-coumaric, protocatechuic, ferulic, caffeic and sinapic acids detected in the rice bran extracts upon fermentation. The highest concentration of coumaric, ferulic and protocatechuic acids in the fermented extracts increased by up to 3.2-fold, 52-fold and 3.2-fold, respectively, in comparison to its unfermented counterpart obtained at the initial phase of fermentation period on day 8 of fermentation. The present investigation demonstrated that SSF enhanced the rice bran by increasing the free total phenolic content as well as phenolic acids concentration with better nutritional and functional properties.