What happens with the glutathione during winemaking and the storage of the wine?

Abstract

We tried to give a part of the answer to this question by monitoring glutathione during winemaking and storage. The novelty of our approach is to quantify simultaneously the three known forms of glutathione: free glutathione (GSH), oxidized form (GSSG) and glutathione-S-sulfonate (GSSO3H). This last molecule was reported first in wine by Arapatsis et al. (2016), who described the reaction between SO2 and GSSG resulting GSH and GSSO3H. Theoretically, GSH can further react with SO2, but this reaction is slow. This results obtained in model wine was now proved in grape juice, by measuring the kinetic of the reaction after the addition of SO2. For this purpose a LC-MS/MS analysis method was developed, which allows for the first time the quantification of GSSO3H beside of GSH and GSSG in the wine. 

The analyses of samples taken in the different moment of winemaking shows that in the must only GSH and GSSG are present. GSSO3H appears after the addition of SO2 at the end of the alcoholic fermentation. It appears also to be the dominant form of glutathione in SO2 containing wines after 3 months storage. The analysis of a hundred of wines showed a correlation between the relative concentration of GSSO3H and the total SO2 level of the wine. Temperature also effects the reaction rate. Grape variety does not seem to influence the formation of GSSO3H. 

We could conclude that SO2 contribute to release active GSH from the GSSG and so extend the protection potential against oxidation during the first months of storage. It remains the questions: Does GSSO3H have any antioxidant activity? Further investigation would be needed to address this question. However, in the meantime, its quantification is important in the wine to avoid underestimating the glutathione content.