Hazard analysis applied to microbial growth in foods: Development of mathematical models describing the effect of water activity

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Abstract
Mathematical models were developed which described the effect of lowering the water activity on the growth kinetics of Staphylococcus aureus and Salmonella typhimurium. By treating the lag phase and exponential phase kinetics separately, predictions can be made on the extent of microbial growth over successive time/temperature cycles. Staphylococcus aureus was far more tolerant than Salmonella typhimurium to lowered water activity; under near growth-limiting conditions of water activity and temperature it showed lag periods as long as .apprx. 40 days. The maximum lag period observed for S. typhimurium was .apprx. 5 days. Under these conditions the predicted generation times for Staphylococcus aureus were 2-3 days and for Salmonella typhimurium, 1-4 days.