Comparison of the Antioxidant Activities between the Proanthocyanidin of a Different Degree of Polymerization from Peanut Skin

Abstract

　The antioxidant activities of the phenolic compounds found in peanut skin is well documented. The aim of the present study was to investigate the structure-activity relationship of these compounds, and more particularly, that of (＋)-catechin (monomer), procyanidin A1 (dimer), and epicatechin-(4β→6)-epicatechin-(2β→O→7,4 β→8)-catechin (EEC, trimer). Their antioxidant properties were compared using four different assays, namely, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, oxygen radical absorbance capacity (ORAC), β-carotene bleaching, and lipid peroxidation in liver microsomal fractions and mitochondria. Our results showed that DPPH radical scavenging activity and ORAC value increased with the number of phenolic hydroxyl groups, in the order EEC > procyanidin A1 ＞(＋)-catechin. On the other hand, using the β-carotene bleaching method, the bleaching activity was inhibited depending on the phenolic molecular weight, in the order (＋)-catechin>procyanidin A1 ＞ EEC. These results might be explained by differential affinity between polyphenols and substrates. In the lipid peroxidation test using rat liver mitochondria and microsomes, the antioxidant activity of both procyanidin A1 and EEC were greater than that of (＋)-catechin.