Metabolomics Analysis of the Effect of Reduced Glutathione on Metabolites of Chardonnay Wine

We undertook this study in order to explore the effect of reduced glutathione (GSH) on the physicochemical indexes and non-volatile and volatile metabolites of Chardonnay wine during a five-month storage period after the end of alcoholic fermentation. Five different concentrations of GSH were added into the wine after the end of alcoholic fermentation. The changes of physicochemical indexes, total phenolic content and color during the storage period were measured. Widely targeted metabolomic analysis and volatile metabolomic analysis based on ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and gas chromatography-mass spectrometry (GC-MS) were performed on wine samples with and without the addition of 20 mg/L GSH. The results showed that during the five-month storage period, the addition of different concentrations of GSH had no significant effect on the volatile acid content, total acid content and pH of white wine (P > 0.05) but significantly influenced its total phenol content, total flavonoid content, color and free SO₂ content. The total phenol content of the wine sample added with 30 mg/L GSH was highest after storage for five months, and the color index of the wine sample added with 20 mg/L GSH was lowest. The addition of GSH could delay the decrease of free SO₂ content. A total of 693 non-volatile metabolites and 816 volatile metabolites were identified. Based on variable importance in projection (VIP) greater than 1.0 and fold change (FC) equal to or greater than 1.4, a total of 33 non-volatile differential metabolites and 22 volatile differential metabolites were selected. Among the 32 non-volatile metabolites, 17 were down-regulated and the rest 16 were up-regulated. Among the 22 volatile metabolites, three were down-regulated and the other 19 were up-regulated. Some phenolic acids, fatty acids and amino acids were associated with changes in volatile metabolites.