Radical Scavenging Action and Its Mode in Procyanidins B-1 and B-3 from Azuki Beans to Peroxyl Radicals

Abstract

Procyanidins B-1 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 × 104 m−1s−1, 5.9 × 104 m−1 s−1, 2.7 × 104 m −1 s−1, 5.0 × 104 m−1 s−1 and 1.1 × 105 m−1 s−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.