The antioxidant properties of green tea, oolong tea, black tea and pu-erh tea were studied using DPPH, ABTS and ORAC assays. Green tea had the strongest antioxidant capacities: 201.504 mg trolox/g for DPPH, 676.117 mg trolox/g for ABTS and 1215.029 mg trolox/g for ORAC. For DPPH and ABTS assays, the kinetics of different teas fitted well with second-order exponential decay equations, and single electron transfer reaction was the major reaction process. For ORAC assay, the decay of fluorescence intensity was accurately predicted by Boltzmann sigmoidal equation, and hydrogen atom transfer reaction was the principal reaction. The antioxidant capacities measured by DPPH, ABTS and ORAC assays were positively correlated to the total phenolics contents in teas, among which (-)-epigallocatechin gallate (EGCg) and (-)-epicatechin (EC) had the highest correlation coefficients with the antioxidant capacities of teas.
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