Formation of Hydrogen Sulfide and Glutathione During Fermentation of White Grape Musts

Abstract

Volatile sulfur compounds (VSCs) and nonvolatile thiol-containing compounds (NVTCs), which are potential precursors of VSCs, were monitored by gas chromatography during fermentation of eight white grape musts: one Thompson Seedless, one Palomino, one Chenin blanc, two Sauvignon blancs, and three Chardonnays. The assimilable amino acid (EAA) concentration of the musts ranged from 480 mg/L to 2022 mg/L (mean = 1131 mg/L). Using a GC-flame photometric detector, three sulfur containing peaks were tentatively identified based on their retention times: hydrogen sulfide (H₂S), ethylmercaptan, dimethylsulfide, and one unknown peak (RT, 9.7 min) was detected. The predominant VSC, H₂S, was continuously produced throughout fermentation and was highest during rapid growth phase of yeast. All juices produced H₂S most rapidly during rapid yeast growth, but musts with low EAA generally produced higher levels of H₂S throughout the fermentation. Total H₂S, which ranged from 112 to 516 mg/L, was inversely correlated with concentration of assimilable amino acids (p < 0.01) and with total nitrogen content (p < 0.10). H₂S at the end of fermentation was negatively correlated with EAA (p < 0.01) and positively with days to dryness (p < 0.05). For all musts, concentration of NVTCs, primarily glutathione (GSH), steadily increased towards the end of fermentation. Final wine concentration of GSH (0.1 to 5.1 mg/L) was correlated with both total N (p < 0.01) and EAA (p < 0.05).