No abstract

Soluble and bound phenolic acids were isolated from Thai rice husk samples at five growth stages during grain development, and their antioxidant activities were evaluated. The results showed that ferulic acid was the major soluble phenolic acid in husk at all stages, and its concentration decreased steadily during grain development. The ratio of ferulic to p-coumaric acid was approximately 2:1 at all stages. The most abundant bound phenolic acid in all extracts was p-coumaric acid, followed by ferulic acid along with traces of syringic, vanilic, and p-hydroxybenzoic acids. Most of the antioxidant activities of soluble and bound phenolic acids in husk extracts were found at flowering stage, and there were high correlations of antioxidant activity to levels of soluble ferulic, gallic, and p-coumaric acids.

This study was designed to investigate the free and bound phenolic acids as well as their antioxidant activities in husk of 12 Thai rice varieties consisting of pigmented rice and normal rice. The pigmented rice husk gave higher free total phenolic contents than normal rice husk. However, there was no significant difference in bound total phenolic contents between pigmented rice and normal rice husks. Ferulic and p-coumaric acids were the major phenolic acids in the free fraction of pigmented rice husks, whereas vanillic acid was the dominant phenolic acid in the free fraction of normal rice husks. On the other hand, p-coumaric acid was highly found in bound form of both pigmented and normal rice husks. The antioxidant activity of husk extracts was positively correlated with the total free phenolics content and individual of phenolic acids especially ferulic acid. On the basis of this study, it is suggested that the rice husk could be a potential phenolic acid source and may therefore offer an effective source of natural antioxidant. Our findings provide valuable information on phenolic acids composition and antioxidant activity of husk for further food application.