Antioxidant capacity of flavanols and gallate esters: pulse radiolysis studies
- 27 December 1999
- journal article
- Published by Elsevier BV in Free Radical Biology & Medicine
- Vol. 27 (11-12), 1413-1426
- https://doi.org/10.1016/s0891-5849(99)00187-2
Abstract
Reactivities of several proanthocyanidins (monomers of condensed tannins) and gallate esters (representing hydrolyzable tannins) with hydroxyl radicals, azide radicals, and superoxide anions were investigated using pulse radiolysis combined with kinetic spectroscopy. We determined the scavenging rate constants and the decay kinetics of the aroxyl radicals both at the wavelength of the semiquinone absorption (275 nm) and the absorption band of the gallate ester ketyl radical (400–420 nm). For most compounds second-order decay kinetics were observed, which reflect disproportionation of the semiquinones. In the case of the oligomeric hydrolysable tannins, pentagalloyl glucose and tannic acid, the decay kinetics were more complex involving sequential first-order and second-order reactions, which could only be resolved by kinetic modeling. A correlation of the reaction rates with hydroxyl radicals (kOH) with the number of adjacent aromatic hydroxyl groups (i.e., representing catechol and/or pyrogallol structures) was obtained for both condensed and hydrolyzable tannins. Similar correlation for the reactions with azide radicals and superoxide anions are less obvious, but exist as well. We consider proanthocyanidins superior radical scavenging agents as compared with the monomeric flavonols and flavones and propose that these substances rather than the flavonoids proper represent the antioxidative principle in red wine and green tea.Keywords
This publication has 56 references indexed in Scilit:
- Tannins and Human Health: A ReviewCritical Reviews in Food Science and Nutrition, 1998
- Procyanidins extracted from pine bark protect α‐tocopherol in ECV 304 endothelial cells challenged by activated RAW 264.7 macrophages: role of nitric oxide and peroxynitriteFEBS Letters, 1998
- Iron complexes of gallocatechins. Antioxidant action or iron regulation?Journal of the Chemical Society, Perkin Transactions 2, 1998
- Tea flavonoids and cardiovascular diseases: A reviewCritical Reviews in Food Science and Nutrition, 1997
- Antioxidants in teaCritical Reviews in Food Science and Nutrition, 1997
- An In Vivo Experimental Protocol for Identifying and Evaluating Dietary Factors That Delay Tumor OnsetPublished by American Chemical Society (ACS) ,1997
- The Relative Antioxidant Potencies of Some Polyphenols in Grapes and WinesPublished by American Chemical Society (ACS) ,1997
- Antioxidant and Prooxidant Behavior of Flavonoids: Structure-Activity RelationshipsFree Radical Biology & Medicine, 1997
- Chemistry of Gallotannin-Derived o-Quinones: Reactivity toward NucleophilesThe Journal of Organic Chemistry, 1995
- The repair of oxidized amino acids by antioxidantsBiochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology, 1984