Water activity and temperature effects on germination and growth of Eurotium amstelodami, E. chevalieri and E. herbariorum isolates from bakery products.

This study investigated the effect of temperature (5-30 degrees C), water activity (0.775-0.90 aw) and their interactions on the temporal rates of germination and mycelial growth of three species of Eurotium on flour wheat sucrose medium. Germination was quite rapid at aw >0.85, with an almost linear increase with time for all isolates. However, under more extreme water stress, germination was slower. The aw minima for germination were usually lower than those for growth and varied with temperature. The effect of aw x temperature interactions on the lag phases (h) prior to germination and on the germination rates (h-1) were predicted using the Gompertz model modified by Zwietering. Eurotium spp. had shown short lag times at 0.90 aw over a wide range of temperatures. At marginal temperatures, lag phases were significantly longer, especially at >15 degrees C. The temperature x aw profiles for mycelial growth varied between species in terms of rates (mm d(-1)). Predictions of the effect of important environmental factors, such as temperature, aw and their interactions on lag times to germination, germination rates and mycelial growth, are important in the development of hurdle technology approaches to predict fungal spoilage in food products.