Reversed-Phase High-Performance Liquid Chromatography-Fluorescence Detection for the Analysis of Glutathione and Its Precursor γ-Glutamyl Cysteine in Wines and Model Wines Supplemented with Oenological Inactive Dry Yeast Preparations

A reversed-phase high-performance liquid chromatography-fluorescence detection methodology involving a pre-column derivatization procedure using 2,3-naphtalenedialdehyde in the presence of 5 and 0.5 mM of dithiothreitol to determine total and reduced glutathione (GSH) and gamma-glutamyl-cysteine (gamma-glu-cys) in musts and wines has been set up and validated. The proposed method showed good linearity (R (2) > 99% for reduced and total GSH, and R (2) > 98% for gamma-glu-cys) in synthetic wines, over a wide range of concentration (0-10 mg L-1). The limits of detection for reduced GSH in synthetic and real wines were almost the same (0.13 and 0.15 mg L-1, respectively) and slightly higher for gamma-glu-cys (0.24 mg L-1). The application of the method allowed knowing, for the first time, the amount of total and reduced GSH and gamma-glu-cys released into synthetic wines by oenological preparations of commercial inactive dry yeast (IDY). In addition, the evolution of these three compounds during the winemaking and shelf life (0-9 months) of an industrially manufactured ros, wine supplemented with a GSH-enriched IDY showed that although GSH is effectively released from IDY, it is rapidly oxidized during alcoholic fermentation, contributing to the higher total GSH content determined in wines supplemented with GSH-enriched IDYs compared to control wines.