Comparison of the survival and metabolic activity of psychrophilic and mesophilic yeasts subjected to freeze-thaw stress.

A mesophilic yeast, Candida utilis, and a psychrophilic yeast, Leucosporidium stokesii, were subjected to freeze-thaw cycling over the range 25 to -60 C. Viability after freeze-thaw stress was directly correlated with the rate of cooling and the physiological age of the cultures. Rates of glucose fermentation and oxidation could be directly correlated with viability. The optimal cooling rate for both yeast strains was 4.5 to 6.5 C/min; however, their levels of survival obtained at this optimal cooling rate varied considerably. In addition, the psychrophile was less resistant to freeze-thaw stress than was the mesophile.