Antioxidant capacities and phenolic compounds of the husk, bran and endosperm of Thai rice

Four fractions, namely, rice bran, rice husk, brown rice and milled rice of a Thai rice variety (Khao Dawk Mali 105), collected from three different growth sites, were analysed to determine phenolic acid composition, γ-oryzanol and tocopherols content and their antioxidant capacity using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and ferric reducing ability power (FRAP) assays. The bran and husk fractions showed higher values of antioxidant activity based on the DPPH and FRAP assays, compared to the other fractions. In addition, the bran fraction had the highest γ-oryzanol and tocopherols content. On the other hand, the husk fraction showed a greater phenolic acids concentration than the other fractions. The three major phenolic acids found in all fractions, despite different growth sites, were ferulic, vanillic and p-coumaric acids. Ferulic acid was most evident in the bran, whereas vanillic and p-coumaric acids were mostly found in the husk. Significant differences (p < 0.05) in the antioxidant capacities of each fraction depended on the growth sites and antioxidant components. We propose that variation in phenolic acid content could be affected by the growth sites. This study demonstrates that rice bran and husk can be considered as valuable sources of bioactive components with high antioxidant properties.