Metabolomics of grape dehydration process

Recently, a mid-way method between “targeted” and “untargeted” analysis (suspect screening analysis) was developed to study grape metabolomics. For the identification of metabolites, a new electronic database of putative grape and wine compounds (GrapeMetabolomics) was expressly constructed which currently contains around 1,100 entries. By performing high-resolution mass spectrometry analysis in a grape extract averaging 320-450 putative compounds are identified, depending on the variety. In the present work this approach was applied to study the chemical changes occurring in grape during dehydration process. In particular, changes in anthocyanins, polyphenols and flavonols, stilbene derivatives, and glycoside aroma precursors, were studied by performing PCA. In the red grape samples an increase of stilbene monomers and oligomers accompanied by decrease of glucoside stilbenes and some other polyphenols, was observed. Flavonols did not change significantly after 15 days, instead a loss of anthocyanins was found after 30 days. These preliminary results indicate the best drying time of these grape varieties under the experimental conditions used to produce raisins wines richer in secondary metabolites.