CHEMICAL MARKERS FOR THE EVALUATION OF SENSORY AND ANTIOXIDANT PROPERTIES OF WINES.

Sotolon (3-Hydroxy-4,5-dimethyl-2(5)-furanone) is a chiral lactone responsible for the oxidized flavour in fortified wines and wine produced by oxidative ageing. The perception threshold of the racemic mixture in wine is 8 – 10 μg/L and the flavour is reported as curry, aged honey, aged sake and fenugreek. Though it is considered a typical flavour note in Madera, Porto and Sherry, it is an off-flavour in dry white wine where its oxidative note is detrimental for the fresh taste and odour. The sotolon formation pathways, during winemaking, are affected by chemical and physical factors such as: oxygen concentration, storage temperature and time, reducing sugar concentration and antioxidant compounds concentration (e.g. sulphur dioxide or (GSH) glutathione). Due to the number of chemical and physical factors affecting the Sotolon formation in wine this compound has been suggested as chemical marker of white wine shelf-life. A fast, sensitive and easy to apply analytical method (UHPLC-UV) and it was applied to the evaluation of SO2-free Franciacorta DOCG wines in order to assess the effect of different disgorgement conditions (antioxidant additives, ageing time and temperature) on the sotolon formation. The sotolon concentration was measured in sparkling wine stored at 15°C and 25°C for 6 months added to three different antioxidant preparations (2 g/hL and 4 g/hL) potentially substituting the sulfur dioxide. Furthermore, we investigated the chemical and physical factors could affect the sotolon formation in synthetic wine. Model solution conitaing increasing concentration of pentoses, GSH, amino group, catechin, oxygen, ethanal, tartaric acid and iron are stored at two temperatures (70°C and 5°C) for five days in order to clarify the compositive factors affecting the sotolon synthesis in white wine. Finally, we compared the performances of analytical methods (HPLC-UV and UHPLC-MS) for sotolon quantification, which were previously developed. Separately, we developed a fast, sensitive and easy to apply analytical method (UHPLC-UV) for the biogenic amines (BAs) assessment in red wine treated with different malolactic fermentation condition (Spontaneous MLF; Inoculum and Co-inoculum techniques). Moreover was checked the trend of intra and extra-cellular glutathione and their effect on the aromatic matrix of South African Sauvignon blanc (Stellenbosch) must and wine during the alcholic fermentation and aging. The Must was treated with GSH and a GSH-enriched inactive dry yeast preparation (GSH-IDYs). The proposed analytical methods (UHPLC-UV; HPLC-UV and UHPLC-MS) provide a sample preparation faster and easier-to-apply than those previously reported for the routine analyses of sotolon. The methods (HPLC-UV; UHPLC-MS/MS; UHPLC-UV) were proved suitable for the determination of sotolon concentrations in white wine and in model solution under its sensory perception threshold. Two analytical methods compared (HPLC-UV; UHPLC-MS/MS) were successfully used for the screening of 70 commercial South African wines’ sotolon levels. The samples of Franciacorta sparkling wines treated with SO2 show the best protection against wine oxidation whereas the other commercial antioxidants tested caused detrimental effects due to the sotolon production. The phenolic composition of commercial antioxidants has influenced the production of sotolon. The sotolon formation tests carried out showed which sotolon can be formed by several formation pathways indeed it was generated under both reducing and oxidative conditions. Sotolon formation is enhanced by simultaneous presence of Fe++ and O2, of amino groups and of phenols. Glutathione inhibited the formation of sotolon only when it was simultaneously added with amino groups and phenols in an oxidizing environment or when it was present in oxidative conditions. Under anoxic conditions the sotolon formation test has been demonstrated that there is a high dependence between sotolon and reducing sugar contents, whereas tartaric acid and acetaldehyde didn't affect the formation of sotolon. The formation of sotolon in anoxic environment has not yet been clarified and further tests will be conduct to understand the role of tartaric acid, ethanol, ethanal and ribose on sotolon production in synthetic wine. The analytical method for the BAs quantification showed good linearity and repeatability and was able to quantify the ABs in red wine. The preliminary results concerning the different malolactic fermentation conditions, suggest that co-inoculum technique does not seem to prevent BAs formation in wine. The trial data on GSH (intra and extra-cellular) have yet to be processed and will be assessed in the future.