Diversity and biology of heat-resistant fungi

Heat-resistant fungi survive high temperatures (75°C or more for at least 30 min). For food microbiology, these fungi are of interest because of spoilage of canned and pasteurized food products, and cause damage for millions of dollars in the fruit-juice and beverage branch. Many studies have been carried out to understand the occurrence of heat-resistant fungi, and research data have indicated that the number of heat-resistant species is increasing. Common fungal genera that contain heat-resistant species are Talaromyces, Neosartorya and Byssochlamys. This chapter provides an overview of the current taxonomical status of these genera and the species belonging to them. Heat-resistant fungi form ascospores that survive pasteurization. External factors, such as presence of organic acids, sugars and pH have an effect on the degree of heat resistance, but heat resistance also depends on endogenous factors like species/strain properties, the age of the ascospores and culturing methods. Furthermore, new processing techniques, like high hydrostatic pressure and pulsed electric fields, prove to have limited success in inactivating ascospores. In the last paragraph, details are given on the biology and mechanisms of ascospores germination of these heat-resistant fungi