Influence of water activity and temperature on the growth of Wallemia sebi: application of a predictive model

Germination and growth of Wallemia sebi were examined on media of a w adjusted with glycerol in the range of 0.96–0.77, at 25°C and 30°C. The effect of temperature on the germination time was significant except between 0.95 and 0.88 a w. At low a w levels as well as above 0.95, the increase of temperature produced an increment in the germination time. The minimum a w for germination was also affected by temperature, being lower at 25°C (0.80 a w) than at 30°C (0.82 a w). Radial growth rates at 25°C were higher than at 30°C. The optimum a w value for growth of W. sebi was 0.94 at both temperatures. The minimum a w for growth was higher than minimum for germination and was also dependent on temperature (0.84 at 25°C and 0.86 at 30°C). An empirical mathematical model was fitted to the measured growth data, providing a good approach to the description of the effect of a w on the radial growth rate of W. sebi.