Quantification of polyphenolic content and bioactive constituents of some commercial rice varieties in Taiwan

Rice (Oryza sativa L.), an important food crop in Asian diets, has been reported to be a good source of bioactive phytonutrients. This study proposed to analyze the free polyphenolic content and their bioactive antioxidative constituents in different grain parts of eleven commercial rice varieties in Taiwan. Results showed that rice bran had the highest total phenolic (1.29–14.27 g GAE/kg) and total flavonoid (1.23–25.83 g QE/kg) contents, followed by brown rice and rice husk; polished rice contained the lowest. The total polyphenolic contents of the Japonica rice varieties were higher than the Indica rice varieties, and the contents in pigmented rice varieties were higher than in non-pigmented rice varieties. Results from high performance liquid chromatographic analysis showed that the major bioactive polyphenolic constituents present in the analyzed rice varieties were ferulic acid, p-coumaric acid, catechin, vanillic acid and caffeic acid. Regardless of the grain parts, ferulic acid was found to be the most abundant and was mainly distributed in rice bran, while p-coumaric acid was present mainly in rice husk.