Role of extraction procedures on the concentration of varietal thiol precursors in Grillo white grape must

Background and Aims Varietal thiol precursors (VTPs) decrease strongly after the pre-fermentative operations. The effect of grape must extraction steps on the concentration of S-3-(hexan-1-ol)-L-glutathione (G-3SH), S-3-(hexan-1-ol)-L-cysteine (Cys-3SH) and S-3-(hexanal)-glutathione (G-3SHal) was investigated. Methods and Results Must produced on a commercial scale was sampled throughout the pre-fermentation steps. Must was also prepared in the laboratory for assessing the role of copper, sulfite and air. In commercial must fractions, over 95% of G-3SHal was lost because of sulfite addition, while the concentration of G-3SH and Cys-3SH increased along with must yield, and it exceeded the concentration found in berries. No Cys-3SH was found in the intact grape; instead a trace concentration of G-SHal, and a high concentration of glutathione and even cysteine was determined when sulfite was added. A large amount of G-3SHal was formed when copper was depleted. Conclusions Our data suggest that Cys-3SH and G-3SHal are promptly and mainly formed in grape must upon grape pressing. Sulfite and copper prevented the formation of VTPs, while settling of must led to a loss of VTPs. Significance of the Study Varietal thiol precursors can be preserved through the proper management of pressing with particular attention to must contact with air, extraction conditions, contact time with solids and addition of sulfite.