Polyphenolic composition and in vitro antioxidant activities of native‐ and tannase‐treated green tea extracts

Summary The antioxidant activities of native‐ and tannase‐treated green tea extracts along with their major polyphenol components were investigated. The polyphenolic content and composition of the tea before and after tannase treatment were determined by liquid chromatography coupled with mass spectrometry (LC‐MS). Approximately 99% of the (−)‐epigallocatechin gallate (EGCG) and (−)‐epicatechin gallate (ECG) in green tea extract were converted by tannase to (−)‐epigallocatechin (EGC) and (−)‐epicatechin (EC), respectively, after 30 min. Biotransformed green tea exhibited a significantly higher DPPH˙ radical scavenging activities than native green tea (EC50 value of 0.024 ± 0.001 and 0.044 ± 0.001 mg mL−1, respectively). Kinetic parameters such as scavenging rate and stoichiometry were calculated. The rate of DPPH˙ radical scavenging activities for tannase‐treated green tea extract was shown to be higher than native green tea extract. Tannase is able to completely degallate EGCG and ECG to EGC and EC in green tea extract, respectively. Tannase‐treated green tea extract exhibited significantly higher DPPH˙ radical scavenging activities than native green tea.