Effects of Metal Ions on Antioxidant Activity of Red Wine

Abstract The biological properties of red wine are attributed to potent antioxidants and the antiradical activity of polyphenols. Recently, it has been noted that metal ions can substantially alter the reactivity of polyphenols. In this study, we observed that the radical scavenging activity of red wine increases when Cu(II), an exemplar of transition metal ions, is either removed or chelated. However, Conversely, the elimination of alkaline earth metal ions such as Mg(II) and Ca(II), representing main group elements, has negligible impact on this activity. We explored the interactions between Cu(II), Mg(II), and Ca(II) with three most abundant phenolic substances –gallic acid, catechin, and caffeic acid – and analyzed the corresponding radical scavenging kinetics in a uniform buffer solution at pH 7.2. Cu(II) formed 1 : 1 complexes with these three polyphenols, substantially diminishing their inherent radical scavenging potential. In accordance with the effect in red wine, Ca(II) and Mg(II) displayed no significant influence on the radical scavenging kinetics of these three polyphenols within the buffer solution. Our findings suggest that the removal of Cu(II), and potentially other transition metal ions, during the wine production process could enhance the antioxidant activity of red wine.