Tannin−Protein Complexes as Radical Scavengers and Radical Sinks

• Published in: Journal of agricultural and food chemistry 2001-10, Vol.49 (10), p.4917-4923
• Main Authors: Riedl, Ken M, Hagerman, Ann E
• Format: Article
• Language: English
• Subjects: Antioxidants - chemistry; Benzothiazoles; Biflavonoids; Biological and medical sciences; Catechin - chemistry; Cations; Food industries; Free Radical Scavengers; Free Radicals; Fundamental and applied biological sciences. Psychology; Gelatin - chemistry; General aspects; Hydrogen-Ion Concentration; Hydrolyzable Tannins - chemistry; Miscellaneous; Proanthocyanidins; Proteins - chemistry; Serum Albumin, Bovine - chemistry; Sulfonic Acids - chemistry
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf010683h

The 2,2‘-azinobis(3-ethylbenzothiazoline 6-sulfonic acid) radical cation (ABTS•+) decolorization assay has been used to determine the antioxidant activity of the polyphenol epicatechin16 (4 → 8) catechin (procyanidin, PC) alone or in complex with the model proteins bovine serum albumin (BSA) or gelatin. PC had a molar antioxidant capacity of approximately 54, 92, or 108 radicals at pH values of 3.0, 4.9, or 7.4, respectively. Radical scavenging occurred via a rapid step followed by a slow step. Interaction with gelatin reduced the rate of rapid scavenging by 50% (PC−BSA mixtures reduced by 15%). Inhibition paralleled formation of precipitable PC−protein complexes over a range of protein/PC ratios. However, inhibition was virtually overcome in 10 min. Reaction with ABTS•+ converted the PC−protein complexes from a dissociable form to a form resistant to dissociation by strong denaturants such as SDS. This study demonstrates that PC is a potent ABTS•+ scavenger even when bound to protein and that the complexes may act as a radical sink within the gastrointestinal tract. Keywords: Procyanidin; condensed tannin; flavonoid; oxidation; recalcitrant; antioxidant capacity; decolorization assay