Combined Effects of α-Tocopherol and Antioxidants on the DPPH Radical Scavenging Reaction

Abstract

　The combined effects of α-tocopherol and various antioxidants were analyzed in a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging reaction system using median effect analysis. Combined effect analysis was performed by mixing various antioxidants individually with α-tocopherol and measuring the DPPH radical scavenging capacity. The combined effects were determined from combination indices (CIs) calculated using the median effect equation. Twelve antioxidants showed synergistic effects, five antioxidants showed additive effects, and one antioxidant showed an antagonistic effect with α-tocopherol at f_a = 0.5 (f_a being the inhibition rate) and a DPPH radical scavenging rate of 50%. Quercetin and rutin, epigallocatechin gallate (EGCg) and myricetin, and epicatechin gallate (ECg), containing catechol structures, pyrogallol structures, and both structures, respectively, have low IC₅₀ values and low CIs at f_a = 0.8 with a DPPH radical scavenging rate of 80%, thereby demonstrating strong synergistic effects with α-tocopherol. EGCg and myricetin exerted particularly strong synergistic effects with α-tocopherol. The antioxidants that showed synergistic effects with α-tocopherol for DPPH radical scavenging were polyphenols with relatively low redox potentials, such as flavanols and flavonols with catechol and pyrogallol structures. These polyphenols showed high DPPH radical scavenging capacities in polar solvents, and they reduced inactive α-tocopheroxyl radicals to regenerate α-tocopherol, thus, exerting synergistic effects with α-tocopherol.