Green tea has four catechin antioxidants (see chemical structures below). The most active antioxidant is (-)-epigallocatechin gallate (EGCG), that has the most phenolic –OH groups, therefore, is used as the surrogate standard for setting its medicinal quality.
The phenolic groups of EGCG serve as electron donors in the sense that they can give up an electron or a hydrogen atom containing an electron without robbing an electron from another atom. These phenolic molecules are capable of making internal adjustment to stabilize their unpaired electron after losing a hydrogen atom. Physiological concentrations of EGCG can prevent free radical-induced chromosomal damage. The two-step hydrogen donation by a phenolic antioxidant is illustrated as follows.