On-line high-performance liquid chromatography analysis of the antioxidant activity of phenolic compounds in green and black tea

Abstract

Teas represent a rich source of dietary antioxidants. This paper describes analysis of the antioxidant potential of individual tea phenolics using an on-line high-performance liquid chromatography (HPLC) method. Tea phenolics from Kenyan green and black teas were identified using liquid chromatography--mass spectrometry (LC-MS(n)) in conjunction with the analysis of their 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid (ABTS+) radical scavenging ability. Antioxidant potential of flavan-3-ols, caffeoylquinic acids, flavonols, and theaflavins was assessed in comparison to the synthetic vitamin E analogue Trolox. (-)-Epigallocatechin gallate was identified as the most potent antioxidant with a Trolox equivalent antioxidant capacity (TEAC) value of 3.0, contributing approximately 30% of the total antioxidant capacity of green tea. Theaflavins retained antioxidant capacity similar to that of (-)-epicatechin monomers whilst conjugated flavonols did not contribute significantly to the antioxidant capacity of either green or black tea. After HPLC analysis of the antioxidant capacity of phenolics in black tea some 80% of antioxidant activity remained unaccounted for indicating the potential importance of thearubigens as antioxidants in black teas.