ENRICHMENT OF THE OENOLOGICAL MALDI-TOF/MS PROTEIN SPECTRA DATABASE FOR RELIABLE OENOLOGICAL YEAST AND BACTERIA IDENTIFICATION

Young white wines are typically released to the market a few months after harvest, to be consumed within a year, when their fresh fruity aromas are still dominant and appealing to modern consumers. Esters, particularly higher alcohol acetates (HAAs) and ethyl esters of fatty acids (EEFAs), play a central role in the fruity expression of young white wines [1]. However, these esters are known to undergo significant hydrolysis during the first months of aging [1, 2].

Oenococcus oeni is the main Lactic Acid Bacteria responsible for malolactic fermentation, converting malic acid into lactic acid and carbon dioxide in wines. Following the alcoholic fermentation, this second fermentation ensures a deacidification and remains essential for the release of aromatic notes and the improvement of microbial stability in many wines. Nevertheless, wine is a harsh environment for microbial growth, especially because of its low pH (between 2.9 and 3.6 depending on the type of wine) and nutrient deficiency. In order to maintain homeostasis and ensure viability, O. oeni possesses different cellular mechanisms including organic acid metabolisms which represent also the major pathway to synthetize energy in wine.

Cognac is a famous spirit produced in southwest France in the region of the eponymous town from wines mainly from Vitis vinifera cv. Ugni blanc. This variety gives very acidic and poorly aromatic base wines for distillation which are produced according to a very specific procedure. Grapes are picked at low sugar concentrations ranging 13-21 °Brix and musts with high turbidity (>500 NTU) are fermented without sulphite addition [1]. Fermentative aromas, as esters and higher alcohols, are currently the main quality markers considered in Cognac spirits.

Non-Saccharomyces yeasts not only increase microbial diversity during wine fermentation, but also have a positive effect on improving wine aroma. Among these non-Saccharomyces yeast species, Metschnikowia pulcherrima is often studied and used in winemaking in recent years, but its application in icewine has been rarely reported. In this study, indigenous M. pulcherrima strains and Saccharomyces cerevisiae strains (commercial and indigenous strains) were sequentially inoculated for icewine fermentations; meanwhile, pure S. cerevisiae fermentations were used as the control; indigenous strains used above were screened from spontaneous fermentations of Vidal blanc icewine.

The pre-fermentative steps play a relevant role for the characteristics of white wine [1]. In particular, the grape pressing can affect the chemical composition and sensory profile and its optimized management leads to the desired extraction of aromas and their precursors, and phenols resulting in a balanced wine [2-4]. These aspects are important especially for must addressed to the sparkling wine as appropriate extraction of phenols is expected being dependent to grape composition, as well.