Untargeted metabolomics analyses to study taste-active compounds released during post-fermentation maceration of wine

Abstract

The sensory properties of a wine depends on its colours, aromas and flavors. Regarding red wines, the gustatory part consists of the acid, bitter and sweet tastes. Even if certain compounds were already identified as contributing to the sweetness, some taste modifications remain largely unexplained. For instance, empirical observations combined with sensory analyzes, have shown that an increase of wine sweetness occurs during post-fermentation maceration. This step is a key stage of red winemaking during which the juice is left in contact with the marc, that contains the solid parts of the grape (seeds, skins and sometimes stems). The present works aims at identifying some compounds responsible for this gain of sweetness. Recent developments have highlighted the interested of untargeted metabolomic analysis for oenology. Using similar tools, an original approach has been developed here to discover new taste-active molecule, The analyses were assayed using liquid chromatography–high resolution mass spectrometry (UHPLC-Q-Exactive Plus, Orbitrap analyzer). Data processing was carried out using the MzMine 2 software followed by a differential analysis and statistical study executed with the R software. To study the effect of post-fermentation maceration, different samples were taken from eight Bordeaux wineries over three vintages. These samples, coming from a total of 240 vats, were collected at two distinct stages, giving rise to two modalities: at the end of alcoholic fermentation and just before running-off the vat, that is after post-fermentation maceration. After LC-HRMS analysis and data processing, a list of ions showing a strong increase during maceration was obtained. The MS2 spectral data, obtained by fragmentation of molecules, provided information for their identification. Some of these ions were selected and considered for a targeted purification by various separative techniques (SPE, CPC and HPLC) which allowed their structural elucidation and sensory characterization in wine.This study proposes new tools to investigate taste-active compounds in wine. More generally, the results bring new insights to understand the chemical origin of wine taste.