Uneven distribution of thiol precursors across red grape berry compartments shapes wine aroma quality: effects of variety, vintage, and skin composition

Varietal thiols are key aroma compounds in wine that exist in grape berries as odorless precursors. They constitute a good field of investigation to (1) assess the varietal potential of hybrids in comparison to Vitis vinifera varieties, by examining their distribution across berry compartments, (2) elucidate the importance of the vintage effect on sensitive varietal compounds; and (3) determine the potential for interactions during precursors’ extraction from grape to must, specifically with cell wall polysaccharides, a topic not yet studied in the literature. This study investigated the influence of variety, vintage and cell wall interactions with thiol precursors as well as their conversion into volatile thiols using standardized vinification process with Vinimag Microvinification device. We analysed the berry compartments (skin, flesh, seeds), musts and wines of 32 varieties 14 Vitis vinifera varieties (Alicante, Cabernet Sauvignon, Carignan, Cinsault, Fer Servadou, Grenache, Petit Verdot, Pinot, Syrah, Tannat, Nielluccio, Pinotage, Touriga Nacional, Xinomavro); and 18 disease-tolerant, interspecific hybrid varieties which possess resistance genes to the principal diseases (downy and powdery mildew), mixing different hybridization programs (1212N, 3160-27-4N, 3176N, 3322-226N, 3328-168N, G14, Artaban, Cabernet Cantor, Cabernet Volos, Monarch, Merlot Khorus, Pinotin, Prior, Sirano, Vidoc, Clinton, Herbemont, Isabelle), harvested in the 2023 vintage. Wines were vinified under standardized microvinification conditions. The vintage effect was assessed with a subset of 11 red grape varieties, harvested in 2024: 7 Vitis vinifera varieties (Carignan, Petit Verdot, Pinot, Syrah, Nielluccio, Pinotage, Touriga Nacional); and 4 interspecific hybrid varieties (G14, Artaban, Prior, Clinton). We analysed 7 thiol precursors (G3SH, Cys3SH, γ-GluCys3SH, CysGly3SH, NAC3SH, G4SMP, Cys4SMP) in berry compartments, musts and their residual contents in wines. Additionally, varietal thiols (3SH, 3SHA and 4SMP) were quantified in wines. Finally, cell wall polysaccharides were analysed with Comprehensive Microarray Polysaccharide Profiling (CoMPP) and grouped in 6 families: cellulose, hemicellulose, homogalacturonans (HGs) and their esterification ratio, Type-I rhamnogalacturonans (RGI), Arabinogalactan Proteins (AGP), and extensins. Data were analysed using a multiparametric statistical approach, including Principal Component Analysis (PCA) and Analysis of Variance (ANOVA).