Growth modelling of heat-resistant fungi: the effect of water activity

Growth of three strains of heat-resistant fungi, Byssochlamys fulva, Neosartorya fischeri and Talaromyces avellaneus, was studied at 25 degrees C at eight or nine water activities (a(w)) adjusted with sucrose between 0.995 and 0.85. The flexible growth model of Baranyi describing the change in colony diameter (mm) with respect to time was first fitted to measured growth data and from the fitted curves the maximum colony growth rates were estimated. These values were fitted with respect to a(w) to predict colony growth rates at any a(w) within the range tested. Optimum a(w) values of 0.986, 0.985, and 0.990 for growth, and maximum colony growth rates of 12.6, 13.2 and 20.2 mm d(-1), respectively, were calculated. The time to reach a colony diameter of 3 mm and the optimum a(w) for each strain were also calculated. The results can be applied to the prevention of spoilage of canned fruit or juices and other heat processed fruit based products.