Antioxidant activity of fractions and subfractions of red rice bran

This study was performed to investigate the antioxidant activity of the fractions and subfractions of red rice bran. Among various solvent fractions (hexane, chloroform, ethyl acetate, butanol, and water fraction), the ethyl acetate fraction showed the highest total phenolics and total flavonoids contents. Compared with those of butylated hydroxytoluene (BHT), the EC ₅₀ values of the ethyl acetate fraction from red rice bran were approximately 2.1 times higher for 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability, approximately 2.5 times higher for 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging ability, and approximately 2.6 times higher for reducing power. Among the various subfractions obtained from the ethyl acetate fraction of red rice bran, subfraction 2 had the highest total phenolics and flavonoids contents. Compared with those of BHT, the EC ₅₀ values of subfraction 2 were approximately 3.3 times higher for DPPH radical scavenging ability, approximately 1.3 times higher for ABTS radical scavenging ability, and approximately 2.6 times higher for reducing power. The phenolic acids in the 40% acetone extract included 61% hydroxylcinnamic acids and 39% hydrobenzoic acids. Ferulic acid was the major phenolic acid in the ethyl acetate fraction and in subfraction 2 isolated from the ethyl acetate fraction of red rice bran. Thus, red rice bran showed significant potential as a natural antioxidant.