Antioxidant properties of 29 tea extracts and catechins were evaluated using 4 different antioxidant assays (DPPH, ABTS, WST-1, and ferric thiocyanate assay). The DPPH and the ABTS assays were used to determine the radical scavenging capacity whereas, the WST-1 assay was used to determine superoxide radical scavenging activity. Inhibition of lipid peroxidation was determined using the ferric thiocyanate assay. Significant correlation was observed between the DPPH assay values and those from the ABTS and WST-1 assays (r＝0.988, 0.953). However, lower correlation was observed for values obtained using the DPPH and the ferric thiocyanate assay (r＝0.556). The total catechin content in tea extracts exhibited strong correlation with the antioxidant values determined using DPPH, ABTS, and WST-1 assays (r＝0.973, 0.964, 0.955). Comparison of the determined antioxidant values and the predicted antioxidant values based on catechin content of the extracts revealed that the contribution of catechins to the whole antioxidant activity of the extracts was 95% for DPPH, 104% for ABTS, 92% for WST-1, and 67% for ferric thiocyanate. These results suggest that compounds in the extract, other than catechins, contributed to the inhibition of lipid peroxidation.
