Polymeric procyanidins as radical-scavenging components in red-hulled rice

The extracts from white-, black-, and red-hulled rice were prepared by sequential extraction with six different polar solvents, and their radical-scavenging activities were measured by methods using 1,1-diphenyl-2-picrylhydrazyl radical (DPPH.) and tert-butyl hydroperoxyl radical (t-BuOO.). The extracts prepared with highly polar solvents, methanol and cleionized water, exhibited higher DPPH. and t-BuOO. scavenging activities in all three cultivars. In addition, the acetone extract from red-hulled rice exhibited a high DPPH. and t-BuOO. scavenging activity, while no such activity was detected for the acetone extracts from white- and black-hulled rice. The major components responsible for the radical scavenging in the acetone extract from red-hulled rice were identified as procyanidins by acidic hydrolysis, vanillin assay, and Sephadex LH-20 chromatography. GPC analysis of the acetylated procyanidins revealed that the average molecular weight is about 5000, in a range of about 500-18 000.