Enzymatic synthesis of theaflavins and epitheaflavic acid from tea catecechns and their antioxidant activity

A number of in vitro and in vivo studies have demonstrated that black tea polyphenols have significant biological activities, including antioxidant, anti-inflammatory and anticancer activity. The theaflavins have received attention as one of responsible components for biological activities of black tea. However, little information is available for the biological activity of individual theaflavins and minor components in black tea. In the present study, theaflavins and epitheaflavic acid were synthesized from their parent flavan-3-ols catechins using an enzymatic oxidation method and employing crude polyphenol oxidase from banana fruit. The compounds were isolated using column chromatographic methods, and their structures confirmed by H-NMR and APCI-MS. The peroxyl radical scavenging activities of theaflavins and epitheaflavic acids were measured using a modified ORAC method. The results indicated that theaflavins have higher peroxyl radical scavenging activity than EGCG. The hierarchy of radical scavenging activity of theaflavins, epitheaflavic acid and related compounds were in the order of: theaflavin-3,3′-digallate ≈ theflavin-3-gallate ≈ theaflavin-3′-gallate ≈ theaflavin > epitheaflavic acid > EGCG > purpurogallin.