Electron spin resonance spectroscopic evaluation of scavenging activity of tea catechins on superoxide radicals generated by a phenazine methosulfate and NADH system

The scavenging effects of tea catechins on superoxide radicals (·O2−) generated non-enzymatically by a phenazine methosulfate (PMS) and reduced β-nicotinamide adenine dinucleotide (NADH) system, was studied using an electron spin resonance (ESR) spectrometer along with a spin-trapping agent, 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO). The presence of 3′, 4′, 5′-trihydroxyl groups attached to the B-ring of the flavan skeleton enhanced the radical scavenging efficiency displayed by the catechin family in comparison to those with 3′, 4′-dihydroxyl groups, and the insertion of a galloyl moiety into three positions of the C-ring exerted a synergistic impact on ·O2− scavenging activity. Catechin constituents accounted for 86% of the total ·O2− scavenging capacity of green tea extract, with a particularly high contribution ascribed to (−)-epigallocatechin gallate [(−)-EGCG] (48%) and (−)-epigallocatechin [(−)-EGC] (26%).