Minimum water activities for the growth of yeasts isolated from high-sugar foods

Minimum water activities (aw) for the growth of 35 yeast strains isolated from high-sugar foods and related materials were determined by incubating in broths containing 1% glucose, 0.5% polypeptone, 0.3% yeast ext., 0.3% malt ext. and aw-controlling solutes at 25°C for up to 120 days. Three kinds of sugars (glucose, fructose, sucrose) and sodium chloride were used as aw-controlling solutes. The minimum aw for growth of the yeasts depended on aw-controlling solutes as well as yeast species and strains. Most species showed the highest minimum aw for growth in NaCl-media and about half of the species showed the lowest minimum aw for growth in sucrose-media. One strain of Zygosaccharomyces rouxii had minimum aw for growth as low as 0.67 in fructose-media. Miso ext. and koji ext., rich in inositol, and casamino acid decreased minimum aw for growth of Z. rouxii in NaCl-media. Pre-incubation in the presence of high concentrations of glucose or fructose also decreased minimum aw for growth of yeasts in glucose-media or fructose-media.