The effect of sulfur compounds on the formation of varietal thiols in Sauvignon Blanc and Istrian Malvasia wines

Abstract

Varietal thiols 3-sulfanylhexan-1-ol (3SH), 3-sulfanylhexyl acetate (3SHA) and 4-methyl-4-sulfanylpentan-2-one (4SMP) are essential for fruity aromas of Sauvignon Blanc wines. The concentration of varietal thiols in wines was thought to be related to the concentration of their precursors in grapes, however only a small proportion of precursors are released to varietal thiols during fermentation. New findings suggested that specific grape juice metabolites could significantly impact on the development of three major varietal thiols and other aroma compounds of Sauvignon Blanc wines. Among them, elemental sulfur and hydrogen sulfide indicated a positive role on the formation of varietal thiols during vinification (Araujo et al., 2016; Harsch et al., 2013). This research aimed to investigate the addition of different sources of sulfur in grape juice on formation of 3SH, 3SHA, 4SMP and benzene methanethiol (BM) in Sauvignon Blanc and Istrian Malvasia wines. Istrian Malvasia (Vitis vinifera L.) is a local grapevine variety which sometimes aromatically resemble on Sauvignon Blanc.Pressed grape juice was settled overnight and sampled from tank for microfermentations. Additions of different sulfur compounds in 700 mL of juice were performed just before yeast inoculation in four replicates each: (1) control – no addition, (2) addition of reduced glutathione (GSH) (20 and 50 mg/L), (3) addition of methionine (10 and 20 mg/L), (4) addition of cysteine (20 and 40 mg/L), (5) addition of elemental sulfur (5 and 10 mg/L) and (6) addition of  sodium hydrosulfide hydrate (1 and 10 mg/L). Fermentations were performed with Saccharomyces cerevisae (X5, Laffort, France) in 750 mL dark glass bottles at 18-20 °C. After fermentation, 50 mg/L SO2 was added, wines were settled, racked, and stored at -20 °C until analyses. Varietal thiols were analysed by GC-MS/MS (Schimadzu, TQ8050) using the modified method as described (Šuklje et al., 2013).Sauvignon Blanc wines with the addition of 10 mg/L NaSH·xH2O (which releases hydrogen sulfide) had significant higher concentration of 3SH and 3SHA compared to control and other treatments. Istrian Malvasia wines with the addition of 10 mg/L NaSH·xH2O had significant higher concentrations of 3SH but there were no significant differences in 3SHA.  The addition of elemental sulfur increased 3SH and 3SHA in both varieties, however not significantly. Addition of sulphur compounds in our study had no effect on concentration of 4MMP and BM in Sauvignon Blanc or Istrian Malvasia wines. On the other hand, the additions of GSH and cysteine resulted in significantly lower formation of 3SH and 3SHA in Sauvignon Blanc wines in comparison to control and other additions. The latter finding is compliant with the study on model wines by Alegre et al. (2019).Modifying sulfur source composition in grape juice showed some significant changes in concentration of 3SH in both Sauvignon Blanc and Istrian Malvasia wines.

References

Araujo D. L., Vannevel S., Buica A., Callerot S., Fedrizzi B., Kilmartin A. P., du Toit J. W. 2016. Indications of the prominent role of elemental sulfur in the formation of the varietal thiol 3-mercaptohexanol in Sauvignon blanc wine, Food Research International, 98, 79-86.