Growth of Osmotolerant Yeasts at Different Water Activity Values

Abstract

The influence of water activity (aw) on growth (lag-phase, mean generation time and cell yield) of osmotolerant yeasts was determined by culturing 7 strains in broths at 10 different aw values in the range of 0.998 to 0.626 and by counting the Colony Forming Unit (CFU) per ml. Broths were adjusted to the desired aw by means of fructose. None of the tested strains could grow at aw 0.701 and 30°C. During 60 d of incubation at this aw and temperature, slight reductions of the initial CFU/ml counts were noted. By incubation at aw <0.701 these reductions were larger. Six strains of Zygosaccharomyces rouxii grew at aw 0.760, whilst a strain of Zygosaccharomyces bailii could not grow at aw <0.858. For six strains the optimum aw for growth was in the range of 0.958 to 0.998. A single strain of Z. rouxii showed optimum aw for growth in the range of 0.913–0.958. Therefore, it was appropriate to redefine it as “osmophilic”. Because of high dehydration, cells actively grown at aw 0.837 were approximately 30% smaller than cells actively grown at aw 0.998.