Combined effects of solutes and food preservatives on rates of inactivation of and colony formation by heated spores and vegetative cells of molds

The combined and independent effects of sucrose, sodium chloride, potassium sorbate, and sodium benzoate on heat inactivation of conidia of Aspergillus flavus and Penicillium puberulum, ascospores of Byssochlamys nivea, and vegetative cells of Geotrichum candidum were studied. In addition, the effects of solutes and preservatives on colony formation by unheated and heated conidia of A. flavus were evaluated. Increased concentrations of sucrose were accompanied by increased tolerance to heat by A. flavus, B. nivea, and G. candidum. Low concentrations (3 and 6%) of sodium chloride protected A. flavus and G. candidum, whereas up to 12% sodium chloride protected B. nivea, but had little effect on the heat stability of P. puberulum. Potassium sorbate and sodium benzoate acted synergistically with heat to inactivate all four molds. At the same concentration, the two preservatives had varied degrees of effectiveness on molds and were influenced by the type of solute in the heating menstrua. Heated conidia of A. flavus had increased sensitivity to preservatives and reduced water activity, whether achieved by the presence of sucrose or sodium chloride, thus demonstrating heat-induced injury. At the same concentration, potassium sorbate was clearly more inhibitory than was sodium benzoate to colony formation by A. flavus, and the presence of sucrose and sodium chloride enhanced this inhibition.