Heat resistance of xerophilic fungi based on microscopical assessment of spore survival.

An improved viable counting technique was developed to facilitate study of the heat resistance of fungal spores. Spores were heated and subsequently incubated in the same medium. After germination, hyphae and germ tubes were stained with lactofuchsin, and the germinated spores were counted with the aid of a microscope. A number of xerophilic strains were examined, mostly isolates from spoiled highmoisture prunes. Of these, ascospores of Aspergillus chevalieri, A. mangini, and Xeromyces bisporus were the most heat-resistant. A decimal reduction curve obtained for A. chevalieri was specified by a z value of 23 F and an F(180) of 2.2 min.