Antioxidant/prooxidant properties of model phenolic compounds: Part I. Studies on equimolar mixtures by chemiluminescence and cyclic voltammetry

The electrochemical behaviour and the antioxidant effectiveness of ascorbic acid (AA), caffeic acid (CA), quercetin (Q), catechin (Cat), hesperetin (H) and their equimolar binary mixtures were evaluated by means of cyclic voltammetry and luminol Co(II)–EDTA chemiluminescence, respectively, with a view to the prediction of a potential prooxidant or synergistic behaviour of mixtures of antioxidants. An important synergistic oxidation between Q and Cat was observed. The mixture CA/AA manifested the most prooxidant tendency among all the tested compounds and their mixtures. AA increased the antioxidant activity of Q and decreased that of Cat. Q and Cat regenerated CA, the prooxidant effect of the mixtures increasing with less e-delocalisation. Cat and CA have an antagonistic effect. H has the closest oxidation potential to CA and a slight increase of its antioxidant activity was registered when mixed with CA, which was not the case when it was combined with the other compounds or measured alone.