In-berry tissue distribution of methyl salicylate free and bound forms in Souvignier gris

Abstract

In recent years, interest in PIWI grapevine varieties has increased markedly. Among disease-resistant cultivars, Souvignier gris -an intraspecific cross between Seyval blanc and Zähringer- has gained considerable popularity among producers and is currently the second most widespread cultivated PIWI variety in Italy. From an oenological perspective, Souvignier gris wines present vegetative and balsamic scents (Roman et al., 2024), consistent with the significant amounts of C6 alcohols and methyl salicylate (Paolini et al., 2023). This latter grape-derived compound, involved in plant defense signaling, plays a key role in defining the aroma profile of wines from some white cultivars (Piergiovanni et al., 2023).

The aim of this study was to investigate the distribution and tissue-specific localization of free methyl salicylate and its glycosylated precursors within the berry and its consequences in winemaking.

Three biological replicates, each comprising 200 Souvignier gris berries, were randomly sampled from a lot of ten bunches, preserving the pedicel, and immediately frozen at -20 °C. For each replicate, 100 g of berries were weighed, manually separated into individual tissues, and subjected to extraction in a 35% (v/v) ethanol solution. Samples were subsequently homogenized, centrifuged, and diluted to a final ethanol concentration of 14%. Solid-phase extraction followed by GC-MSMS and HPLC-MSMS analyses was performed on each tissue for all replicates.

Results indicated that, in Souvignier gris, methyl salicylate (MeSA) was predominantly stored in glycosylated form across all berry tissues. The main bound form was MeSA-gentiobioside, which accounted for more than 90% of total MeSA precursors, while other conjugates -such as rutinoside, violutoside, glucoside, and primeveroside- played only a minor role.

More than 65% of total MeSA precursors were localized in the pulp and seeds, whereas the free form of MeSA was mainly associated with the skins, which contained approximately 80% of total free MeSA. This contrasting distribution highlights a marked tissue-specific compartmentalization between bound and free forms of the compound. Results were further confirmed at winemaking conditions and, coherently with pulp predominance, prefermentation cold-soaking had limited effect on the concentration of MeSA in the corresponding wines.

References

Paolini et al., (2023). In: II International Congress on Grapevine and WineSciences, Logroño, La Rioja (Spain), 8-10 November 2023.

Piergiovanni et al., (2023). OENO one, 57(2), 115-127.

Roman (2024). In: 38th EFFoST International Conference 2024: Future Food Systems: Innovation through Progress at Scientific Interfaces, Bruges, Belgium, 12-14 November 2024: P2.1.029.