Antioxidant activity of condensed tannins of beach pea, canola hulls, evening primrose, and faba bean

Condensed tannins were extracted from beach pea, Cyclone canola hulls, evening primrose and faba bean using 70% aqueous acetone. The dried crude tannin extracts were purified on a Sephadex LH-20 column using first 95% ethanol as a mobile phase for elution of nontannin phenolics and then 50% aqueous acetone to elute tannins. The total content of polyphenolics in tannin extracts ranged between 10 and 405 mg catechin equivalents per 1 g extract. All tannins extracts displayed a marked antioxidant activity in a beta-carotene-linoleate model system. Evening primrose and faba bean tannin extracts exhibited the best preventive effect against the bleaching of beta-carotene after a 120 min period. The scavenging effect of tannin extracts on alpha,alpha-diphenyl-beta-picrylhydrazyl (DPPH) radical, at a dose of 0.5 mg, ranged from 35% to 75.4%. The condensed tannins of evening primrose exhibited a significantly (P<0.01) greater scavenging effect far DPPH radical than other tannin extracts. The reducing power of beach pea and evening primrose tannin extracts on potassium ferricyanide was greater than that of other tannin extracts examined.