Finding of remarkable synergistic effect on the aroxyl-radical-scavenging rates under the coexistence of α-tocopherol and catechins

Measurements of aroxyl radical (ArO center dot)-scavenging rate constants (ks AOH ) of antioxidants (AOHs) (alpha-tocopherol (alpha-TocH) and three catechins (CatHs) (ie, epicatechin (EC), epigallocatechin (EGC), and epigallocatechin gallate (EGCG)) were performed in ethanol solution, using stopped-flow spectrophotometry. ks AOH values were measured not only for each AOH, but also for the mixtures of two AOHs (alpha-TocH and CatH). A notable synergistic effect that the ks alpha- TocH value of alpha-TocH increases 1.29, 1.84, and 1.65 times under the coexistence of constant concentrations of EC, EGC, and EGCG, respectively, was observed for the solutions including alpha-TocH and CatH. Similarly, ks CatH values of CatHs (EC, EGC, and EGCG) increased 1.72, 2.25, and 2.34 times under the coexistence of constant concentrations of alpha-TocH, respectively. UV-Vis absorption of alpha-tocopheroxyl radical (alpha-Toc(center dot)) (lambda(max) = 428 nm), which had been produced by reaction of alpha-TocH with ArO center dot, decreased remarkably under the coexistence of alpha-TocH and CatHs due to the fast alpha-TocH-regeneration reaction by CatHs. The result suggests that the prooxidant reaction due to alpha-Toc(center dot) is suppressed by the coexistence of CatHs. By analyzing the formation and decay curves of alpha-Toc(center dot), it has been ascertained that one molecule of EGCG having three OH groups at B-ring may rapidly regenerate three molecules of alpha-Toc(center dot) to alpha-TocH.