Influence of wine pH on changes in color and polyphenol composition induced by micro-oxygenation

The presence of oxygen in red wine leads to the transformation of ethanol into ethanal, which after capturing a proton will react with flavanols to start the process of forming ethyl bridges between flavanols and between flavanols and anthocyanins. Wine pH also conditions the equilibrium between the different anthocyanin structures and may thus affect anthocyanin reactivity. Consequently, the aim of this paper was to study how the pH can affect the changes induced by micro-oxygenation in two wines with different phenolic composition. The differences between micro-oxygenated wines and their controls were, in general, greater when the pH was more acidic. Specifically, the differences between micro-oxygenated wines and their corresponding controls in terms of color intensity, anthocyanin concentration, PVPP index, ethyl-linked pigments, B-type vitisins, polymeric pigments, and ethylidene-bridged flavanols were greater at lower pH. In contrast, the effects of micro-oxygenation when the pH was less acidic were much less evident and sometimes practically nonexistent. These results demonstrate for the first time that the pH of the wine has a great influence on oxygen-induced changes of color and phenolic compounds.