Quantification of the production of hydrogen peroxide H2O2 during wine oxidation
Abstract
Chemical studies aiming at assessing how a wine reacts towards oxidation usually focus on the characterization of wine constituents, such as polyphenols, or oxidation products. As an alternative, the key oxidation intermediate hydrogen peroxide H2O2 has never been quantified, although it plays a pivotal role in wine oxidation. H2O2 is obtained from molecular oxygen as the result of a first cascade of oxidation reactions involving metal ions and polyphenols. The produced H2O2 then reacts in a second cascade of oxidation to produce reactive hydroxyl radicals that can attack almost any chemical substrate in wine. Here, we show that based on an assay used in biotechnological analytics, the Amplex Red Assay, a fluorescence method can be developed to quantify H2O2 in wine. The non-fluorescent Amplex Red reagent was catalytically converted into a fluorescent product in presence of H2O2. Wine samples were left to react with oxygen during 30 min before read out. The fluorescence intensity provided quantification of the total integrated production of H2O2 during the measurement period. Within-day as well as between-day variabilities were small (CV < 1%, respectively 1.5%). H2O2 levels were very low in white wines compared to red wines demonstrating the importance of polyphenols. Moreover, H2O2 increased with temperature and the addition of metal ions. By contrast, H2O2 levels did not correlate with the concentration of many common wine constituents such as polyphenols or sulphur dioxide except for polymerized pigments, which played a major role. Furthermore, H2O2 levels were independent of the anti-oxidant properties of the wines. In general, this study demonstrates that the oxidation reactions in wines involve a complex interplay of chemical species that can only be grasped using a holistic approach. We speculate that this novel concept of quantifying the production of intermediates by trapping, using a fluorescent reporter, will open the path to detailed studies aiming at deciphering oxidation mechanisms in wines.
Issue: Macrowine 2016
Type: Poster
Authors
*HES-SO