Antioxidant and photo-antioxidant abilities of catechins

Catechins are studied vigorously, in particular, concerning the antioxidant ability as polyphenol, which is generally considered responsible for photo-antioxidant natures of catechins. In this study, the andoxidant and photo-antioxidant abilities of (+)-catechin, (-)-epicatechin, and epigallocatechin have been investigated kinetically and discussed in detail. As a result, this study clarifies that a strong antioxidant is not always a good photo-antioxidant as well as that catechins show a high antioxidant ability in an initial oxidation process and acquire a photo-antioxidant ability with the progress of photo-oxidation. In particular, (+)-catechin and (-)-epicatechin convert into quercetin to show a remarkable photo-anti oxidant ability almost comparable to quercetin. In this case, (-)-epicatechin has a higher photo-antioxidant ability than (+)-catechin, although they differ only in the configurations. These facts are explained by the direct conversion of the catechins into quercetin. (c) 2008 Elsevier B.V. All rights reserved.