Combined Effect of Polyphenols and Cysteine or Glutathione in DPPH Radical Scavenging Reaction

Abstract

　In radical scavenging reactions under conditions where polyphenols and thiols coexist, not only does each demonstrate an antioxidant reaction, but the synergistic effect between both is exhibited as thiols regenerate polyphenols. This study combined polyphenols and cysteine (Cys) or glutathione (GSH) in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging reaction system and analyzed the combined effect by median effect analysis. In combination with Cys, it showed a strong synergistic effect with flavanols having galloyl groups, such as epicatechin gallate (ECg) and epigallocatechin gallate, and flavonols having pyrogallol structures, such as myricetin, at high concentration ranges. Meanwhile, in combination with GSH, a strong synergistic effect was shown with polyphenols having catechol structures, such as catechin, epicatechin, ECg and quercetin. In both cases, it was suggested that thiols strongly exhibit synergistic effects when combined with polyphenols with catechols, pyrogallols, or galloyl groups having a high radical scavenging capacity and low redox potential. Therefore, it was suggested that the nucleophilic reaction of Cys and GSH with polyphenols having these properties and the regeneration of phenolic hydroxy groups exert the synergistic effect of radical scavenging activity.