Mechanism change in estimating of antioxidant activity of phenolic compounds.

The 2,2'-diphenyl-1-picrylhydrazyl (DPPH(•)) method is commonly applied for the estimation of antioxidant activity of single compounds and plant extracts. In this method, the amount of disappeared DPPH(•) in the examined system, determined spectrophotometrically, is a measure of the antioxidative (hydrogen-donating) activity of compounds. The present paper discusses the influence of buffer components on the estimation of antioxidant activity of phenolic compounds by this method. According to the obtained results, the change of hydrogen ion concentration changes the mechanism of scavenging process of DPPH radicals by phenolic antioxidants, and the introduction of metal ions into measuring system blocks the scavenging process of DPPH radicals. Both factors depend on the anion type used in the measuring system. The presented results may be especially important for the researches examining plant extract which differ in the content and composition of natural acids and metal ions, and for those who investigate the mechanisms of the reaction applied for the estimation of antioxidant properties.