Physiological characteristics of fungi associated with dairy products

Knowledge about physiological characteristics of food-borne fungi is important in understanding how the environment affects colonization of different foods and feeds. The response of a fungus to changes in the environment will, however, depend on the stage of the life cycle or the physiological mode of the mycelium. Germination of spores is a key event in the fungal life cycle giving rise to colonization by a growing mycelium. Understanding of the factors controlling germination are of major importance as no infection of food-stuffs will occur if spores do not germinate. Food spoilage and production of mycotoxins and other secondary metabolites represent two other areas of great concern in relation to food spoilage, which might be controlled by different regulation mechanisms. Detailed as well as more general information on behaviour of fungi in relation to important growth controlling factors are therefore needed. The methods to be used must match each experimental setup, preferable in a multifactorial design. Fungal developments are in the presented work characterized by the environmental factors: incubation time, temperature, water activity (aw), NaCl-contents, pH, and levels of carbon dioxide and oxygen concentrations in the incubation atmosphere. Conidia from the common cheese spoiler Penicillium commune is present on hard cheeses when they are packaged for further distribution. To simulate this situation, "dry conidia" were kept in sealed vials for 14 to 56 days under various atmospheric conditions and different levels of relative humidity (r.h.). Germination and growth were followed by using an impedi-metric method. The results showed that conidia survived all experimental conditions and started growth when they were transferred to a growth medium. The lag times after prolonged storage (56 days) and the growth rate were affected by levels of r.h. and carbon dioxide. It was demonstrated that low levels (