Modelling bacterial growth of Listeria monocytogenes as a function of water activity, pH and temperature.

Temperature, pH and water activity are important factors controlling the microbiological safety of foods. To describe the growth rate of Listeria monocytogenes in relation to these factors, two equations have been developed. Both equations are based upon the Ratkowsky equation for temperature and growth rate. The first equation predicts growth rate at sub-optimal pH values, sub-optimal temperatures and sub-optimal water activities, the second model predicts growth throughout the entire pH range. The first model may be used to predict growth rates between pH 4.6-6.7, temperature range 5-35 degrees C and a water activity range of 0.95-0.997. The second model is valid throughout the pH range of 4.6-7.4 and the same temperature and water activity range as the first model.