UNDERSTANDING WINE TERROIR: METABOLOMIC APPROACHES TO UNVEIL THE INFLUENCE OF SOIL ON THE CHEMICAL COMPOSITION OF NERO D’AVOLA GRAPES AND WINES

The aim of this PhD project was to unveil the soil effect on the chemical composition of grapes and wines from Vitis vinifera cv. Nero d’Avola. The study focused on six soil chemical-physical parameters, namely texture, pH, total carbonates, cation exchange capacity, electric conductivity, and organic matter. The soil effect on grapes quality was studied through the observation of berries ripening kinetics (e.g., ripeness homogeneity and maturation rate) and of the evolution of phenolic compounds in grapes during the ripening process. The soil effect on wines quality was considered by studying the phenolic and volatile organic composition of Nero d’Avola wines, as determined by chromatography-based metabolomic approaches. Moreover, wines metabolome was investigated through 1H-NMR-based metabolomic analysis. Two different approaches were applied: the targeted (TA) and the non-targeted one (NTA). The former differentiated the wines by profiling (i.e., by identifying and quantifying) a number of different metabolites. The latter provided wine fingerprinting by processing the entire spectra with multivariate statistical analysis. NTA also allowed investigation of the hydrogen bond network inside wines, via the analysis of 1H-NMR chemical shift dispersions. Results showed that soil had a significant effect on grapes ripening and composition, as well as wines composition. On the one hand, it was observed that cation exchange capacity and soil texture had a remarkable impact on phenolic composition. On the other hand, cation exchange capacity and organic matter affected wines volatile organic composition, particularly the fermentative composition. Results obtained by 1H-NMR-based metabolomics showed that the differences among wines were due not only to the concentrations of the various analytes but also to the characteristics of the H-bond network where the different solutes are involved. The H-bond network affects both gustatory and olfactory perceptions by modulating the way how solutes interact with the human sensorial receptors. Moreover, the aforementioned H-bond network is also related to the soil properties from which the grapes were taken. The importance of our findings lies in the fact that, despite the pivotal role played by soil in grapevine growth, only little information was available about the effect of some soil chemical-physical parameters on grapes and wine chemical composition. Therefore, the present study can be considered as a good attempt to investigate terroir, i.e. the relationship between grapes and wine quality and soil characteristics.