First large-scale study of thiol precursor distribution in red grape berry compartments and implications for thiol-type red wine production

Abstract

Climate change and the growing need to reduce the use of phytosanitary products demand the exploration of disease-resistant grape varieties and/or adapted to drought conditions. Integrating data corresponding to red wine quality markers, such as aromas, as early as possible in the varietal selection process, and understanding the extraction and production mechanisms of these molecules of interest, is a major challenge for the wine industry, in order to select varieties with interesting oenological properties. Varietal thiols, namely 3-sulfanylhexan-1-ol (3SH), its acetate (3SHA) and 4-sulfanyl-4-methylpentan-2-one (4SMP) are an important group of aroma compounds responsible for grapefruit, goyava or blackcurrant bud notes in wines respectively. In berries, varietal thiols occurred as odorless S-conjugate precursors to cysteine, glutathione or dipeptide derivatives. Lots of studies have been conducted on thiol precursors of white grapes [1, 2] but data dealing for red grapes are still scarce and even more in the case of interspecific hybrid varieties [3, 4]. The “thiol potential” which refers to 6 thiol precursors (cysteinylated and glutathionylated precursors of 3SH and 4SMP as well as dipeptidic forms for 3SH only) was characterized for 32 red grape varieties cultivated in Occitanie (south of France) in different berry compartments (skin, pulp and seeds) and musts. Finally, the thiol concentration (3SH and 3SHA) was measured in wines produced with those varieties.

In berries, significant differences in the precursor content were observed between the different varieties from 1.1 µg/kg for Xinomavro to 117.9 µg/kg for Pinot Noir. The precursor content was analyzed in the different berry compartments (skin, flesh and seeds) and balanced regarding the relative proportion of each in a whole berry. As for white varieties, the most abundant thiol precursor in berries and must is G3SH for all red studied grapes, independently of the cultivar category (Vitis vinifera, interspecific hybrid). During standardized micro-scale fermentations, thiol precursors are quickly consumed during the first 2 days of AF and corresponding thiols are formed concomitantly. Levels of varietal thiols can pick up to 1556 ng/L for 3176N Bouquet variety to dramatically decrease to levels below to 18 ng/L for Cinsault in all the final wines, highlighting potential trapping of thiols with electrophile species.

References

[1] Roland, A., Schneider, R., Charrier, F., Cavelier, F., Rossignol, M., & Razungles, A. (2011). 125(1), 139–144.

[2] Peyrot des Gachons, C., Tominaga, T., Dubourdieu, D. (2002) Am J Enol Vitic.  53(2): 144-146.

[3] Nicolle, P., Gerzhova, A., Roland, A., Dagan, L., Delpech, S., Gagné, F., & Pedneault, K. (2022). OENO One, 56(3), 357–369.

[4] Nicolini, G.; Roman, T.; Flamini, R.; Tonidandel, L.; Gardiman, M.; Larcher, R. (2020). J Sci Food Agric, 100 (7), 3262–3268.