UNTARGETED METABOLOMICS ANALYSES TO IDENTIFY A NEW SWEET COMPOUND RELEASED DURING POST-FERMENTATION MACERATION OF WINE

Abstract

The gustatory balance of dry wines is centered on three flavors, sourness, bitterness and sweetness. Even if certain compounds were already identified as contributing to sweetness, some taste modifications remain largely unexplained1,2. Some empirical observations combined with sensory analyzes have shown that an increase of wine sweetness occurs during post-fermentation maceration³. 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). This work aimed to identify a new taste-active compound that contributes to this gain of sweetness. Recent developments have highlighted the interested of untargeted metabolomic analysis for oenology4,5. Using similar tools, an original approach has been developed here to discover new sweet molecules released during post-fermentation maceration. In this context, 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 before and after post-fermentation maceration. 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 obtain a list of ions showing a strong increase during maceration. The MS² spectral data, obtained by fragmentation of molecules, provided informa-tion for their identification. One of these ions was selected and considered for a targeted purification by various separative techniques (SPE, CPC and HPLC-preparative). Its structural elucidation by NMR allowed to identify this compound for the first time in wine. Furthermore, sensory analysis revealed its pronounced sweet taste. 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 and open promising perspectives for practical applications.