Rationalizing The Wine Nucleophilic Competition For Quinone Addition

Abstract

Protecting white wine against early oxidation is a worldwide issue, because the uncontrolled oxidation of wine promotes aromatic loss and color browning which lead to wine unacceptance by consumers. These changes are mainly driven by the consumption of oxygen by polyphenols leading to the production of quinones which are oxidant compounds. Quinones can react with numerous nucleophilic compounds notably aromatic thiols, decreasing the aromatic bouquet of the wine.

The nucleophilic addition reaction of standard compounds on 4 methyl-1,2-benzoquinone (4MeQ) can be monitored over time by mass spectrometry (MS). The addition of GSH on 4MeQ follows an apparent first order kinetic which is easy to monitor and fit with simple mathematical model. The best fit with first order kinetic (adjusted R² > 0.98) enables to estimate GSH-half-life which is related to the effective competition of other compounds present in solution. This model firstly applied on model solution with known concentrations in nucleophilic compounds (amino acids, peptpides), was then used to estimate the nucleophilic activity of inactivated yeast’s soluble fractions to classify these enological additives. The GSH-half-life ranged from 4.6 to 69.3 hours depending on the GSH accumulation process initially involved in the yeast enrichment process. Our results clearly show that the process of glutathione accumulation in yeast favors the co-accumulation of additional nucleophilic compounds, with the most interesting consequence that the GSH itself appears to be preserved. This methodology reveals that the kinetics of reference nucleophiles addition to a quinone, can rationalize the non-GSH fraction contribution to the global nucleophilic properties of complex matrices.