Rice bran fermentation by lactic acid bacteria to enhance antioxidant activities and increase the ferulic acid, ρ-coumaric acid, and γ-oryzanol content

Rice bran is considered a natural source of antioxidants. In this study, rice bran was fermented with lactic acid bacteria to increase its antioxidant activity. Four strains isolated from fermented food, Lactobacillus plantarum MJM60383, Lactococcus lactis subsp. lactis MJM60392, Lactobacillus fermentum MJM60393, and Lactobacillus paracasei MJM60396, were confirmed as safe through stability tests such as safety assessment for biogenic amine production, hemolytic activity, and mucin degradation, and showed high reducing capacity. The antioxidant activity of rice bran fermentation altered by these strains was evaluated using several methods including measurement of $Fe^{2+}$ chelating activity and scavenging activity by 1,1-diphenyl-2-picryl-hydrazil (DPPH), 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and nitric oxide assays. In this study, the total phenolic content and ${\gamma}$-oryzanol were evaluated by high-performance liquid chromatography. Compared to non-fermented rice bran and a commercial product, rice bran fermented with Lactococcus lactis subsp. lactis MJM60392 showed the highest phenolic content (844.13 mg GAE/g). Moreover, the content of ferulic acids, ${\rho}$-coumaric acid, and ${\gamma}$-oryzanol in rice bran increased after fermentation with L. lactis subsp. lactis MJM60392 and L. fermentum MJM60393 compared to other samples. Indeed, the DPPH radical scavenging activity and NO scavenging activity were also found to be high in these fermented rice brans. These results indicated that fermentation with lactic acid bacteria increases the active compound levels and the potent antioxidant activities of rice bran.