Abstract
Summary: The response of 31 ascomycetous yeasts to a reduction in water activity (aW) adjusted with D-glucose or NaCl was investigated. The growth of most yeasts was more tolerant to glucose than to NaCl at equivalent aW. Zygosaccharomyces rouxii was the most osmotolerant yeast examined. Natural abundance 13C-NMR spectroscopy and HPLC analyses of eight yeasts indicated that glycerol and arabitol or mannitol were accumulated intracellularly in response to aW. reduction. Pichia sorbitophila, Candida cacaoi, Candida magnoliae and Zygosaccharomyces bisporus responded to reduced aW by a decrease in specific growth rate and cell volume, and an accumulation of glycerol. The other polyol accumulated did not increase in concentration with aW reduction to the same degree as glycerol. A polyol concentration ratio (intra/extracellular) as high as 800-fold was attained across the membrane. Greater amounts of polyols were produced at equivalent aW values when adjusted with glucose than with NaCl. The ability to accumulate high concentrations of polyols appears to be the most important criterion in determining osmotolerance.
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