Increasing the antioxidant power of tea extracts by biotransformation of polyphenols

► Antioxidant power of green tea and yerba mate biotransformed by tannase was tested. ► Tea extracts, chlorogenic acid and EGCG were assessed using ORAC and DPPH assays. ► Green tea antioxidant power of enzyme-treated increased 55% compared to untreated tea. ► Yerba mate antioxidant power increased by 43% compared to untreated tea. ► The antioxidant power of the standards was also highly increased by enzyme treatment.