Bound Phenolic Compounds and Antioxidant Properties of Whole Grain and Bran of White, Red and Black Rice

Total phenolic content (TPC), individual phenolic acid and antioxidant capacity of whole grain and bran fraction 18 rices with different bran color were investigated. The levels of TPC in bound fractions were significantly higher than those in the free fractions either in the whole grains or brans. The main bound phenolic acids in white rice samples were ferulic acid, p-coumaric acid, and isoferulic acid, and in pigmented rice samples were ferulic acid, p-coumaric acid, and vanillic acid. The protocatechuic acid and 2,5-dihydroxybenzoic acid were not detected in white samples. The content of gallic acid, protocatechuic acid, 2,5-dihydroxybenzoic acid, ferulic acid, sinapic acid had significantly positive correlations with TPC and antioxidant capacity. This study found much wider diversity in the phenolics and antioxidant capacity in the whole grain and brans of rice, and will provide new opportunities to further improvement of rice with enhanced levels of the phytochemicals.