Hence, it has four diastereoisomers with two of the isomers are in trans configuration, and the other two are in cis configuration. The trans and cis isomers are referred to as the catechin and epicatechin, respectively. These chemical structures appear to be important for the antioxidant activities of tea polyphenols, including an ortho-3 0 4 0 dihydroxyl group or 304050-trihydroxyl group in the B-ring, a gallate group located at the 3 position of the C-ring, and hydroxyl groups at the 5 and 7 positions of the A-ring . Many structure–activity relationship investiga- tions have been performed on the antioxidant activity of flavonoids, including tea catechins