Synergistic Effects of Potassium Sorbate and Sodium Benzoate on Thermal Inactivation of Yeasts

ABSTRACT Experiments were conducted to evaluate and compare the combined effects of two preservatives, potassium sorbate and sodium benzoate, with heat on inactivation and injury of 12 strains of yeasts. There does not appear to be any correlation between ability to sporulate and z value or general heat sensitivity. Heat treatment caused an increase in sensitivities of 10 of the 12 strains to potassium sorbate (≤ 1000 ppm) as evidenced by inability to form colonies in the presence of the preservative in a recovery medium. Heated cells of five test strains had increased sensitivity to ≤ 1000 ppm of sodium benzoate. Whether exposed to potassium sorbate or not during heating, 100 ppm of the preservative in recovery broth severely retarded, and in some instances completely inhibited, growth of yeasts for a period of 10 hr post treatment. These results strongly suggest that yeasts possessing a wide range of physiological characteristics are subject to heat‐injury and, furthermore, that postassium sorbate enhances injury during heating and retards or prevents repair of injury during recovery. Sensitivity to heat generally increased as the pH of the heating medium decreased from 7.0 to 2.5. Without exception, the presence of 500 ppm of potassium sorbate or sodium benzoate in the heating medium caused more rapid inactivation rates of yeasts compared to heating in the absence of preservatives. At comparable concentrations, sodium benzoate was less effective than was potassium sorbate, which exerted a significant (P ≤ 0.05) effect on increasing the rate of heat inactivation at concentrations as low as 50 ppm.