New hypotheses about wine phenolic evolution revealed by untargeted metabolomic profiling of wine micro-oxygenation

Metabolomics is a state-of-art technique for unbiased and question-driven analysis of metabolome changes. When combined with multivariate data analysis, it leads to a powerful tool to determine the differences between complete metabolomic fingerprints and to identify the candidate biomarkers. Wine micro-oxygenation is a common winemaking practice for red wine, that consists in a continuous addition of small amounts of oxygen into the wine in order to improve its color, aroma, texture and its positive evolution during ageing. Although being widely used and studied for decades, not all the mechanisms occurring during this mild exposure of wine to oxygen are completely known. Moreover, no analytical tools are available to winemakers in order to control the process. Object of our project was to study the wine micro-oxygenation through LC-MS untargeted metabolomic profiling. For this purpose, the effect of two wine micro-oxygenation experiments, one before and one after the malolactic fermentation, were studied by untargeted UPLC-QTOF MS, allowing to profile >1000 components of Sangiovese wines. The design of this experiment allowed us to investigate the influence of oxygen and iron on the wine composition. Using the chromatographic and spectral data set of our laboratory and information from the literature it was possible to annotate more than 250 compounds in wines. The data analysis through supervised and unsupervised multivariate methods highlighted findings that revealed new hypothesis regarding the formation and evolution of polyphenols during wine ageing. In specific, among the candidate biomarkers were identified various pigments, tannins and other phenolics known to be influenced by micro-oxygenation, but also some primary and secondary metabolites never taken in consideration before. In addition, it was experimentally demonstrated for the first time the correlation between the pigments formation and various metabolites of the citric acid cycle. These outcomes allowed us to provide a most comprehensive picture of the minute changes in wine composition associated with the micro-oxygenation. These findings could be useful for developing analytical tools able to help researchers and winemakers for a more appropriate design and control of the wine micro-oxygenation.