Role of Oxygen in Wine: Fundamental Understanding of the Oxygen Oxidative Cascade
A theory of wine oxidation was developed based on prior experiments and the published literature. This theory has been described at an ASEV meeting and will soon be published in AJEV. One part of that theory suggested that hydrogen peroxide was not a strong oxidant, but instead iron salts were necessary for hydrogen peroxide to exert an oxidative effect via the Fenton reaction. In this reaction, the extremely reactive oxidant, the hydroxyl radical, should react with any organic substance present in wine, in rough proportion to their concentration. Consequently, antioxidants would have minor only effects on stopping this reaction. Since glycerol is a major component in wine, but no one had ever described its oxidation products in wine, we tested our theory by oxidizing it using hydrogen peroxide, with and without iron. It only oxidized with added iron to yield glyceraldehyde and dihydroxyacetone. These products were also formed along with acetaldehyde when alcohol was present. These products also appeared in wine when oxidized, and when added to red wine, caused it to darken, suggesting that like acetaldehyde, they are able to convert grape anthocyanins to wine pigments. Therefore, these reactions support our new theory that the Fenton reaction is a key to understanding wine oxidation.
This theory also suggests there are many other oxidation products that have not been discovered and which may also participate in wine pigment formation as well as other wine aging products. This result opens the door to a broader understanding of wine oxidation that, once developed, should provide winemakers with much better control of oxidation and predictive tools for utilizing oxidation in improving wine quality.
These products were quantified using a new analysis procedure based on dinitrophenylhydrazine derivatives, a procedure developed as part of the study. This new analytical method can be applied to the production of any aldehydes or ketones formed in wine oxidation and a full report is in preparation. This method should have broad application in monitoring wine oxidation.