Genetic characterization and phenotypic variability in Torulaspora delbrueckii species: Potential applications in the wine industry

In this study, several strains of Torulaspora delbrueckii yeast species were evaluated in the laboratory for their enological properties. In a preliminary step, the ability of different molecular methods to discriminate among T. delbrueckii strains was compared. A combination of 7 PCR methods was able to separate 21 strains into 18 groups, while an REA-PFGE method allowed, in one experiment, the separation into 19 groups. The T. delbrueckii strains used presented a wide phenotypic variability in fermentation behaviour, e.g. Lag Phase (LP) duration, T50 parameter (time necessary to ferment half the sugar), and ethanol production. These 3 parameters have to be considered for industrial selection, particularly the LP duration. The majority of T. delbrueckii strains produced 8 to 11% and 7 to 10% ethanol vol. at 17 °C and 24 °C, respectively, with a maximum ethanol concentration of 12.35 at 17 °C and 10.90% vol. at 24 °C. The phenotypic variability of this species was also reflected in volatile acidity, glycerol, and aroma production. These experiments confirmed the low volatile acidity and glycerol production of this species and revealed a difference in osmotic stress response, compared to Saccharomyces cerevisiae. T. delbrueckii presented high fermentation purity and produced low levels of undesirable volatile compounds, such as hydrogen sulphide and volatile phenols.