Automated HPLC analysis of glutathione and thiol-containing compounds in grape juice and wine using pre-column derivatization with fluorescence detection

An easy and sensitive method for the analysis of glutathione (GSH) and other thiol-containing compounds in grape juice and wine has been developed and optimized. Following a pre-column derivatization of thiols with o-phthalaldehyde (OPA) and 2 aminoethanol, isoindole derivatives are separated on reversed-phase HPLC column and quantified by a fluorescence detector. The minimum detection limits for thiols are: GSH, 3.3 nmol/l (1 μg/l); cysteine, 22 μmol/l (2.7 mg/L); methanethiol, 0.27 μmol/l (12.8 μg/l); ethanethiol, 0.65 μmol/l (11 μg/l). The method yields linear responses up to 40 and 21 mg/l for GSH and cysteine, respectively. GSH levels in two varietal grape juices during fermentation varied from 0 (starting juice) to 2.1 mg/l (wine) in Sauvignon blanc, while the GSH in a Palomino sample with 1.28 mg/l in the juice increased to 5.1 mg/l in the wine. This automated pre-column derivatization of thiols followed by an automatic injection procedure is sensitive, reproducible and rapid, with a run time of 35 min.