INTERACTIVE EFFECTS OF SOLUTES, POTASSIUM SORBATE AND INCUBATION-TEMPERATURE ON GROWTH, HEAT-RESISTANCE AND TOLERANCE TO FREEZING OF ZYGOSACCHAROMYCES-ROUXII

The interactive effects of solutes, potassium sorbate and incubation temperature on growth, heat resistance and tolerance to freezing of Zygosaccharomyces rouxii were investigated. Growth rates in media supplemented with glucose, sucrose or NaCl to a(w) 0.93 were more rapid than in unsupplemented media (a(w) 0.99). Although growth in unsupplemented medium was lower at 35-degrees-C, incubation at 21-degrees-C or 35-degrees-C had little effect on growth in media supplemented with glucose and sucrose. The addition of 300 mug potassium sorbate/ml to media resulted in reduced growth rates, particularly at 35-degrees-C. Heat resistance of Z. rouxii was substantially greater in cultures previously incubated at 35-degrees-C than in cultures incubated at 21-degrees-C in media both with and without 300 mug potassium sorbate/ml. Zygosaccharomyces rouxii was tolerant to freezing at - 18-degrees-C for up to 120 d in all test media supplemented with glucose, sucrose or NaCl. The addition of 300 mug potassium sorbate/ml to sucrose-supplemented media resulted in increased resistance to freezing in cultures previously incubated at 21-degrees-C. Sensitivity to freezing increased when cultures were incubated at 21-degrees-C in media not supplemented with solutes. Glucose and sucrose provided the best protection against inactivation by heating and freezing, regardless of the presence of potassium sorbate in growth media.