Predictive microbiology and food safety

The evaluation of risk in food safety requires knowledge of the probability that microbial population sizes will not exceed defined levels. This probability is evaluated assuming that the growth of the microbial population can be described by the Gompertz equation with the variance of growth depending on the population size. It is shown that the probability density associated with this phenomenon is skewed, so that the risk of a high microbial population is greater than that which would be estimated using a symmetrical probability distribution such as the Gaussian. Maximum likelihood estimates of the parameters of the Gompertz equation based on the derived probability density are calculated using data published by Zwietering et al. [23] for the growth of Lactobacillus plantarum under different temperatures. The probability that a microbial population of a given size will exceed an unacceptable level within a given time is calculated for growth at two temperatures, 10 and 25°C. The implication of these theoretical results for the management of risk in food safety and in the design of hazard analysis critical control point procedures is discussed.