Impact of agronomical and technological factors and the oxidative protection of the matrix on polysulfide formation and atypical ageing in wine

Wine is an alcoholic beverage which has been important in human nutrition for centuries. Oenological research is expanding, focusing on different aspects, including sensory science, wine technology and wine chemistry. The latter aims to gain more understanding of the chemical processes involved in winemaking, both during and after vinification. Oxidation reactions have intrigued the wine sector due to their potential adverse effect on the quality of the final product. Post-bottling wine faults are most feared by wine producers as these alterations are more difficult to foresee and prevent, and their negative impact on the bouquet could be detrimental. White wines are more susceptible to oxidative defects and could lead to the fate of important aromas or the synthesis of compounds with an unpleasant sensorial character. The aim of this doctoral research was to apply an analytical approach using ultra high-pressure liquid chromatography coupled to high-resolution mass spectrometry in order to detect and study the relevant compounds involved in the expression of two of the most important white wine defects. In particular, reductive notes caused by hydrogen sulfide (H2S) resulting from polysulfides (PSs) formation and subsequent degradation and off-odour formation from atypical ageing (ATA) were assessed. In order to improve the analytical detection of PSs in different model wines and musts, an on-line solid phase extraction (SPE) cartridge was implemented prior to chromatographic separation. The method was successfully applied on different matrices, revealing several cysteinylated and glutathionyl PSs and allowing the characterisation of 21 PSs from oxidised varietal volatile thiols. Subsequently, the method was used to study various possible factors involved in the formation of PSs during fermentation. The role of copper and sulfur was demonstrated in fermenting synthetic and Chardonnay musts, the impact of different oenological yeasts was proven, and different glutathionyl trisulfides 18 were detected in traditional sparkling wines. Furthermore, the chemical degradation of PSs was investigated using UHPLC with an integrated fraction collection in order to obtain the cysteinyl pentasulfide (CS5C) from a solution with a mix of PSs. This technique made it possible to study the evolution of a single compound and its degradation products, despite the unavailability of a commercial analytical standard. In addition, the collected fraction was analysed using ion-exchange chromatography, revealing the possible release of hydrogen sulfide from the pentasulfide. Finally, the protective capacity of the matrix was evaluated for its role in the development of the two oxidative defects from PSs and ATA. In particular, the effect of antioxidant supplementation of grape must on the development of ATA during wine ageing was verified, demonstrating the most effective adjuvants to slow down AAP accumulation. Moreover, the oxygen radical absorbance capacity (ORAC) in relation to ATA development was investigated by analysing a selection of different white wines from different origins in Italy. A tendency of a correlation between ORAC and AAP formation was demonstrated for the first time. In contrast, a preliminary study did not show a clear relationship between ORAC and PSs accumulation, suggesting that other factors different from antiradical capacity play a more determinative for the presence of PSs in wine.