Investigating the germination and growth kinetic of Aspergillus fumigatus isolated from cake under different conditions of aw and temperature

The impact of aw (0.65-0.9), temperature (15-30°C) and their interaction on the germination and radius growth of Aspergillus fumigatus isolated from cake was surveyed on Yeast Extract Glucose Chloramphenicol Agar (YGC-Agar) during 60 days as well as the capabilities of Gompertz and Logistic models for fitting data were explored. Rising aw (from 0.65 to 0.9) and temperature (from 15 to 25°C) caused significant enhancing of germination and growth rate of A. fumigatus (P < 0.05). However, in constant aws, further increasing of temperature (up to 30°C) led to meaningful decreasing of these parameters (P < 0.05). A. fumigatus did not germinate at aw 0.65. In addition, germination was observed at aw 0.7 and 0.75 only when the temperature was 15 and 25°C while the mycelium growth was not occurred at these conditions. Although the germination rate was relatively high at aw 0.8, the mycelium growth was very limited. The most amount of germination and radius growth was for aw 0.85 -0.9 and temperature 15-25°C (P < 0.05). Consequently, the optimum growth of A. fumigatus was seen at aw 0.9 and temperature 25°C and the best shelf life of cake proved at aw < 0.7. Furthermore, fitting the growth curves demonstrated the more accuracy of Logistic model rather than Gomperts model.