Comparison of antioxidant activity of wine phenolic compounds and metabolites in vitro

A comparative study of the antioxidant activity of wine phenolics has been performed. Standards of phenolic compounds, including benzoic and cinnamic acids, flavanols, flavonols and resveratrol, as well as some of their metabolites have been analysed for their antioxidant activity. Antioxidant assays included the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging methods and the Oxygen Radical Absorbance Capacity method (ORAC). We compared the reactivity of standard phenolic compounds under selected tests and obtained a ranking order for each one. Both ABTS and DPPH methods were well correlated. Several new structure–activity relationships were observed. As the number of phenoxyl groups increases, the antioxidant capacity, determined by DPPH and ABTS tests, improves. In the case of the ORAC assay, the ortho-position of phenoxyl groups clearly determines the activity. The metabolites of phenolic compounds present antioxidant activity and their values are similar to those of the phenolic compounds themselves. The choice of solvent, the effect of concentration and the information provided by the three tests under study are considered.