Assay of glutathione in must and wines using capillary electrophoresis and laser-induced fluorescence detection: Changes in concentration in dry white wines during alcoholic fermentation and aging

Glutathione (GSH) was assayed in must and wine using capillary electrophoresis coupled with laser-induced fluorescence (LIF) detection. Sample preparation involved conjugating thiols with monobromobimane (MBB) in a 2-(N-cyclohexylamino)ethanesulfonic acid [CHES] buffer (179 mM). The electrophoretic conditions were 30 kV with a capillary length of 105 cm from the inlet to the detector (120 cm total length) and a 50 μm inner diameter. Under these conditions, the complete separation from the other main non-volatile thiols took less than 20 min. We also described the optimum conditions for derivatizing wine samples with MBB to increase eletrophoretic sensitivity. The detection limit for glutathione assay is 65 nmol/L. This simple, sensitive method provides a specific assay of glutathione in reduced form, as the sample preparation technique does not modify the balance of oxidized and reduced forms. We used this method to monitor changes in the reduced glutathione content of a white wine during alcoholic fermentation and barrel aging.