Antioxidant activity of procyanidin-containing plant extracts at different pHs

Anti-oxidant activity was measured for a Pinus radiata bark extract (bark 1), a Pinus maritima bark extract (bark 2), two grape seed extracts, three grape skin extracts, catechin, trolox, ascorbic acid (vitamin C) and calcium ascorbate. The activity was analyzed as ability to scavenge superoxide radicals in a hypoxanthine-xanthine oxidase system, using NBT and WST-1 assays. The 50% inhibition (IC50) of formazan formation was estimated for the samples studied. This study demonstrated that, in basic solution, bark extracts were 13 times more effective antioxidants than vitamin C; however, in aqueous and acidic solutions, bark1 acted as a more potent antioxidant than the other antioxidants in the NBT assay. Grape seed extracts 1 and 2 acted as moderate antioxidants in aqueous and basic solutions in both NBT and WST-1 assays and, in most cases, were three times as efficient as vitamin C. Activities of grape skin extracts were in the same range as trolox, being about 10 times lower than that of the bark extracts. Statistical analysis showed that there was no significant difference between the two assay methods or pH of the solution.