CONICET | Buscador de Institutos y Recursos Humanos

In the winemaking process, alcoholic fermentations are currently conducted using starters of selected strains of Saccharomyces cerevisiae. In recent years, the use of autochthonous strains as starter cultures has increased, since these yeasts are better adapted to the micro-environmental conditions of a specific wine-producing region and also they are endowed with exceptional enological properties and capable of producing an assortment of flavor compounds apparently contributing to the specific bouquet of locally produced wines.The aim of this study was to evaluate the effectiveness of an autochthonous strain of S. cerevisiae in Malbec wines elaborated at industrial scale. The indigenous strain was previously isolated and selected by our laboratory from grape berries of San Rafael-Mendoza (Argentina) wine-growing region.Malbec (Vitis vinífera) grapes at high maturity level (sugar 243.0 g/L, titratable acidity 3.37 g/L, pH 3.90) were destemmed, crushed and sulphited (50 mg/L). Fermentations were carried out in 70 hL stainless steel tanks at temperature range of 17-26 ºC. The autochthonous strain was added as starter consisting of pre-fermented must (160 L). Initial cell density in the tank was 4.00x106 colony-forming units (CFU)/mL. In addition, a control vinification was carried out with a commercial yeast (ENARTIS Ferm Red Fruit). During the contact period of the liquid with the solids, two daily pumpovers were made and both temperature and density were controlled. Samples were taken daily to perform the microbiological study, which consisted of total yeast counts in YPD medium (Yeast extract Peptone Dextrose), as well as differential counting in WL (Wallerstein Laboratory), which allowed a presumptive identification of the isolates. The implantation of the autochthonous strain was verified by means of molecular identification through of the analysis of the mitochondrial DNA restriction fragments length polymorphisms (mtDNA-RFLP) using the endonuclease Hinf I. After 8 days of fermentation (residual sugar less than 2 g/L), the devatting of the wines was made and they were sulphited (30 mg / L) and stabilized for 30 days at 15 °C. Oenological parameters (ethanol, total and volatile acidity, pH, residual sugar and SO2) were determined according to the official methods proposed by the OIV.The results showed a similar fermentative kinetics for both autochthonous and commercial strains, reaching an initial population nearby 108 CFU/mL on the second day of fermentation. From the fourth day of fermentation, the autochthonous strain viable cell population began to gradually decrease, maintaining a count of around 106 CFU/mL until the end of the fermentation. While the commercial strain maintained a cell density around 107 CFU/mL during the stationary phase and then decreased markedly. Regarding the differential count, the proportion of No-Saccharomyces/Saccharomyces yeasts was lower in the winemaking with the autochthonous yeast than in the commercial one. This indicated a greater predominance of the indigenous strain over the total microbiota found. On the other hand, the molecular analysis results confirmed the autochthonous strain implantation throughout the fermentation process. At the end of the fermentation, the wine made with the indigenous yeast had a chemical composition similar to that of the control wine. Both wines reached an ethanol content of 14.2 and 14.4% (v/v), respectively. The other analytical parameters were within the expected and acceptable values. Additional studies for the evaluation of flavor compounds, chromatic characteristics, as well as the sensory analysis of wines are being carried out.Therefore, the use of the autochthonous yeast could potentially contribute to the differentiation of regional wines and improve the competitiveness of the productive sector.

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