Oxygen Consumption in South African Sauvignon Blanc Wines: Role of Glutathione, Sulphur Dioxide and Certain Phenolics

The aim of this research was to investigate the interaction between sulphur dioxide, glutathione (GSH) andcertain phenols in the presence of oxygen in a synthetic wine and in clarified Sauvignon blanc wine. In thisstudy, the clarified wine, from which most of the phenols had been removed, was compared to syntheticwine solution, with both mediums being enriched with caffeic acid to investigate the effect of different levelsof sulphur dioxide and GSH on oxygen consumption. Moreover, thirteen young South African Sauvignonblanc wines with different levels of sulphur dioxide were oxygenated, and the oxygen consumption andphenolic and colour changes were monitored over time. The results show that oxygen consumption wasinfluenced greatly by the presence of sulphur dioxide and, to a lesser extent, by the presence of GSH,with both compounds decreasing during the course of the experiment. During oxidation, an increasewas observed in glutathionyl caffeic acid, as well as in oxidised glutathione (GSSG); however, this didnot coincide with the percentage decrease in GSH. Oxidation further led to an increase in absorbancemeasurements at 420 and 440 nm (yellow-orange colour), which were reduced by the presence of SO2. Alarge variation was also observed in the oxygen consumption of the young wines, with this rate increasingwith an increase in SO2 concentration. Positive correlations were also observed between oxygen, SO2, GSHand Cu concentrations, which were again negatively correlated with absorbance at 420 and 440 nm andGSSG concentrations