CONTRIBUTION OF VOLATILE THIOLS TO THE AROMA OF RIESLING WINES FROM THREE REGIONS IN GERMANY AND FRANCE (RHEINGAU, MOSEL, AND ALSACE)

Abstract

Riesling wines are appreciated for their diverse aromas, ranging from the fruity fresh characters in young vintages to the fragrant empyreumatic notes developed with aging. Wine tasters often refer to Riesling wines as prime examples showcasing terroir, with their typical aroma profiles reflecting the geographical provenance of the wine. However, the molecular basis of the distinctive aromas of these varietal wines from major Riesling producing regions in Europe have not been fully elucidated. In this study, new lights were shed on the chemical characterization and the sensory contribution of volatile thiols to Riesling wines from Rheingau, Mosel, and Alsace. First, Riesling wines (n = 46) from the three regions were collected and assessed for their aroma typicality by an expert panel. Based on sensory assessment, selected wines were examined for their global aroma profile by sensory guided odorant screening techniques (preparative high pressure liquid chromatography; gas chromatography–mass spectrometry/olfactometry (GC–MS/O); sensory evaluation), and several odorous zones (OZs) of interest resembling the original olfactory notes (citrus, tropical fruits etc.) of the initial wines were noted. The aroma descriptors, linear retention index, and mass spectra of the suspected chromatography peaks and their accompanying OZs of interest revealed the presence and importance of volatile thiols in Riesling wines analysed. Hence, selective silver ion solid phase extraction and multidimensional GC–MS/O were applied for further characterization of targeted thiol-relevant OZs, allowing tentative identification of unknown thiols, with one new mercapto monoterpenoid confirmed by orthogonal approach. Following the sensory guided qualitative screening efforts, a new and highly sensitive quantitation method based on chemical derivatization and liquid chromatography quadrupole Orbitrap high-resolution MS was developed for the analysis of a substantial number of known and newly identified volatile thiols in the wine set. Quantitative results confirmed the relevance of 13 odorous thiols in Riesling, with several of them presented at concentrations well over their perception thresholds, as 3-sulfanylhexanol for instance. Thus, the combination of the chemical analysis of thiols and the sensory evaluation made it possible to draw up regional profiles according to the origin of the wines.