Investigation of the potential synergistic effect of resveratrol with other phenolic compounds: A case of binary phenolic mixtures

Although the antioxidant activity of individual phenolic compounds is widely described, there is a lack of information about their interactions and potential synergistic or antagonistic effects. In this study the interaction between resveratrol and other phenolics (gallic acid, caffeic acid, catechin, quercetin) in equimolar binary mixtures was investigated using three different antioxidant assays (FRAP, DPPH, and Briggs–Rauscher reaction). The obtained results indicate that there are differences in the activity of mixture of phenolic compounds and resveratrol depending on mechanism of the used method. The synergistic effect between catechin and resveratrol was confirmed using all three methods. The reducing activity of the mixture of caffeic acid and resveratrol was almost 10.0% higher than the activity of the individual compounds, while in the other two assays that evaluate free radical scavenging activity of the samples, this phenolic mixture showed antagonistic effect. Significantly prolonged inhibition time, and extremely enhanced effect of mixtures of gallic acid and resveratrol and of catechin and resveratrol, by 45.5 and 53.3% respectively, was detected using Briggs–Rauscher reaction. The obtained results support the fact that the antioxidant activity of phenolic mixtures cannot be predicted from the activity of pure compounds, but they could be useful in the explanation of the activity of their mixtures.