Effects of potassium sorbate on growth patterns, morphology, and heat resistance of Zygosaccharomyces rouxii at reduced water activity.

Abstract

A study was made of the effects of potassium sorbate on growth, morphology, and heat sensitivity of an osmotolerant yeast, Zygosaccharomyces rouxii, grown in media (water activity (aw) 0.93) supplemented with glucose and sucrose. Growth patterns of Z. rouxii in YM broth supplemented with glucose (YMBG) and sucrose (YMBS) were similar, although increased potassium sorbate concentration in both media resulted in decreased growth rates. Growth in YMBS containing potassium sorbate was not as prolific as that in YMBG containing potassium sorbate. Inhibition of growth was indicated by decreased absorbance (at 600 nm) of cells grown in YMBS and in YMBG and YMBS supplemented with potassium sorbate at 600 or 1000 micrograms/mL. Slight decreases in cell size and alteration of cellular morphology were associated with increased potassium sorbate concentration. Plasmolysis increased as potassium sorbate concentration was elevated in YMBS but not in YMBG. Tolerance of Z. rouxii to potassium sorbate was enhanced by previous adaptation of cells in media with elevated potassium sorbate concentrations. Heat resistance of cells unadapted to potassium sorbate showed little or no increase regardless of culture age, but increased substantially in cells grown in media containing potassium sorbate, particularly YMBS.