Antioxidative properties of proanthocyanidins. Part ii. Radical scavenging action and its mode in procyanidins B-1 and B-3 from azuki beans to peroxyl radicals.
Procyanidins B-l and B-3 from azuki beans showed remarkable scavenging activities, especially to hydrophilic radicals. The inhibition rate constants for the scavenging of hydrophilic peroxyl radicals generated from 2, 2'-azobis(2-amidinopropane)hydrochloride in aqueous media were calculated at 37°C to be kinh = 6.0×104M-1s-1, 5.9×104M-1s-1, 2.7×104M-1s-1, 5.0×104M-1s-1 and 1.1 × 105M-1s-1, and the stoichiometric factors as n=8.4, 8.0, 3.7, 1.2 and 1.7 for procyanidin B-1, procyanidin B-3, (+)-catechin, ascorbic acid and α-tocopherol, respectively. Thus, the dimeric procyanidin molecule could trap eight radicals. The production and structures of procyanidin B-3 radicals are discussed on the basis of the ESR spectra observed by autoxidation of procyanidin B-3 in an aqueous alkaline methanol solution.