Six genera of yeasts possessing a wide range of physiological characteristics were tested for their sensitivities to heat when suspended in media (pH 4.5) with reduced water activities (aw). Five of six strains had increased tolerance to heat, compared to controls, when cells were suspended in broth containing 3% sodium chloride. Further protection was afforded to three strains in broth containing 6% salt, whereas one strain showed increased tolerance to heat when sodium chloride was present in broth at a concentration of 12% (aw = 0.926). Sucrose, at levels up to 60% (aw = 0.892), protected five of six strains against heat inactivation. Addition of potassium sorbate or sodium benzoate at 500 or 1000 ppm to heating menstrua resulted in significantly decreased D values for all yeasts. At the same concentration, the extent to which the two preservatives acted synergistically with heat was dependent upon the nature of the solute used to lower the aw of the heating media.

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