Effect of metal chelators, ascorbate, glutathione and phloroglucinol on red wine oxidation

Recent studies in wine oxidation have demonstrated the importance of endogenous transition metal catalysts on wine phenolic oxidation. In this experiment the effect of metal chelators on suppression of red wine oxidation was investigated. The chelators examined were ethylenediaminetetraacetic acid (EDTA), deferoxamine and 2, 2-bipyridine. It was expected that possible disruption of redox cycling due to addition of metal chelators to red wine would be observable. Furthermore, additional additives ascorbate, glutathione and phloroglucinol, were evaluated for ability to increase oxidation rates. Ultimately, oxidation rates were investigated in this way to gain enhanced mechanistic understanding of wine oxidation, allowing for development of new tools designed to better control oxidation during the process of making wine. Along with metal chelators and additional additives, catalytic concentrations of iron, copper and iron with copper were added to experimental red wine. Oxidation rate was determined by measuring oxygen. The more oxygen consumption over a given period of time, the more accelerated the oxidation. Dissolved oxygen measurements were taken using a Fibox PC-controlled fiber-optic oxygen meter in conjunction with Oxygen Sensor Spots fixed inside each transparent experimental vessel. This new method for measuring dissolved oxygen that allows for oxygen measurement without opening experimental vessels was investigated for possible future experimental and industrial applications. Deferoxamine was found to depress and ascorbate to accelerate oxidation rate best of all additives investigated across all metal treatments in this red wine, demonstrating that changes in oxidation rates due to addition of various additives using this method were observable. However, the small magnitude of oxidation rate changes implies that the additives investigated lack chemical qualities desired for potential future commercial applications. As previously found in model wine, in red wine the iron plus copper metal treatment exhibited the highest oxidation rates and the no metal added treatment exhibited the lowest oxidation rates. Wine and wine plus metal treatments presented similar reaction rates, suggesting initial metal concentrations in experimental wine were sufficient for catalytic redox cycling required for oxidation reactions. However, initial oxygen addition treatments exhibited higher oxidation rates than delayed oxygen addition treatments, indicating there may be a change in the metal species present. Future research should investigate this effect in greater detail.