Structural elucidation, distribution and antioxidant activity of bound phenolics from whole grain brown rice

Abstract

Chemical profiles, distribution, and antioxidant activity of bound phenolics from brown rice were investigated. Four new dehydrodiferulic acid dimers (DFA) along with eighteen known phenolics were isolated from brown rice bound phenolic extracts and their structures were determined by multiple spectroscopic methods. Among them, ferulic acid and 8-5' DFA were the most abundant monomeric and dimeric bound phenolics in brown rice, rice bran and polished rice. In whole brown rice, polished rice contributed more than 50% of three phenolic monomers and six phenolic dimers, while rice bran contributed more than half of the other thirteen phenolics including eight monomers, four dimers, and one trimer. All the isolated compounds exhibited oxygen radical absorbance capacity. Thomasidioic acid, caffeic acid, methyl caffeate, and 8-5' DC DFA displayed potent peroxyl radical scavenging capacity, and the last three compounds also showed moderate cellular antioxidant activity.

Keywords: 4-Hydroxybenzaldehyde (PubChem CID126); Antioxidant activity; Bound phenolics; Brown rice; Caffeic acid (PubChem CID689043); Distribution; Ferulic acid (PubChem CID445858); Methyl caffeate (PubChem CID689075); Methyl ferulate (PubChem CID5357283); Methyl p-Hydroxycinnamate (PubChem CID5319562); Structural elucidation; Syringic acid (PubChem CID10742); Vanillic acid (PubChem CID8468); p-Coumaric acid (PubChem CID637542); p-Hydroxybenzoic acid (PubChem CID135).