Ethanol tolerance of five non-Saccharomyces wine yeasts in comparison with a strain of Saccharomyces cerevisiae: influence of different culture conditions

The kinetics of cell inactivation at high concentrations of ethanol (22.5% and 25% v v-1) was studied with particular reference to the influence of different cultivation conditions (aerobiosis, semi-aerobiosis, anaerobiosis, addition of survival factors) prior to ethanol challenge. The levels of fatty acids and sterols in cells grown under these different conditions were analysed in order to derive a potential relationship between the ethanol tolerance and the lipid composition of the different strains studied. Under the conditions tested, Hanseniaspora guilliermondii showed an ethanol tolerance very similar to that of Saccharomyces cerevisiae, and very different to that of the other apiculate yeast, H. uvarum. The survival of S. cerevisiae and H. guilliermondii at 25% (v v-1) ethanol was strongly influenced by the conditions of cultivation prior to the ethanol challenge. A small increase in survival was observed for H. uvarum and Torulaspora delbrueckii in the cultures grown in aerobiosis. Growth of these yeasts in anaerobiosis in the presence of added ergosterol and Tween 80 (as a source of oleic acid) did not induce a considerable tolerance to the ethanol challenge, in spite of the incorporation of these compounds by the cells. In these growth conditions Debaryomyces hansenii was not capable of incorporating the survival factors and did not increase the ethanol tolerance. It is shown in this work that, besides S. cerevisiae, the presence of oxygen and the addition of survival factors to the culture conditions and the subsequent increase in the proportion of cell sterols and unsaturated fatty acids may play an important role in the ethanol tolerance of some non-Saccharomyces yeasts. This effect was not, however, observed in all of the yeasts studied.