Two kinds of dimeric procyanidins were isolated in pure form from azuki beans by preparative HPLC. They were identified as procyanidins B-1 and B-3, on the basis of their UV, IR FAB-MS and ¹H-NMR spectra, and an analysis of the acid hydrolyzed products. The procyanidins were evaluated as antioxidants for linoleic acid in an aqueous linoleic acid-β-carotene model system. In the range of the tested concentrations (5 × 10^-5 - 100 × 10^-5%) and pH values (7-9), they showed remarkable antioxidative activities. Their activities were much stronger than those of such commercially available natural antioxidants as ascorbic acid, γ-oryzanol, gallic acid, L-tryptophan, (+)-catechin and D-α-tocopherol. The hydrogen- or electron-donating activities of procyanidins to the DPPH radical in a 50% ethanol solution were also stronger than those of ascorbic acid and D-α-tocopherol.

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