Experiments were conducted to determine if two preservatives, potassium sorbate and sodium benzoate, had a synergistic effect with heat on inactivation of conidia of Aspergillus flavus and Penicillium puberulum and vegetative cells of Geotrichum candidum. A second objective was to determine if heated conidia had increased sensitivity to preservatives in a recovery medium. As the pH of heating menstrua was decreased from 7.0 to 2.5, the rates of inactivation of molds were increased. Conidia were not as adversely affected by acid pH as were vegetative cells. At 50 ppm, potassium sorbate caused a significant (P⩽0.05) increase in the rate of thermal inactivation of A. flavus and G. candidum; 100 ppm had a significant effect on P. puberulum. Sodium benzoate caused significant decreases in decimal reduction times of A. flavus and P. puberulum when present at a concentration of 50 ppm in heating media. Viable heated conidia of A. flavus and P. puberulum had increased sensitivity to potassium sorbate and sodium benzoate, indicating heat injury. However, the relative effects of the two preservatives on colony formation in recovery agar were reversed from those noted in heating media, i.e., at comparable concentrations, potassium sorbate was more effective than was sodium benzoate for inhibiting colony formation.

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