Microbial growth and survival: Developments in predictive modelling

Traditionally, microbiologists have attempted to understand food preservation via challenge tests, the differences between the microbiology of the initial and stored product being interpreted by retrospective consideration of the physical and chemical conditions during storage. Such studies are slow, expensive, and are only relevant to the product and conditions tested. Most foods are nutrient-rich, but microbial growth is often determined by a small number of factors e.g. pH, aw, temperature, atmosphere, preservatives, particular organic acids, and only occasionally particular nutrients. Many stable food products are the result of preservative factors acting in combination, but our understanding is poor. The concept of ‘predictive microbiology’ was proposed, with growth responses of microbes of concern in foods modelled with respect to the main controlling factors — initially temperature, pH and water activity. Models relevant to broad categories of foods would reduce greatly the need for ad hoc microbiological examination of new food products and enable predictions of shelf-life and safety via a computerized database, with considerable financial benefit. Initial scepticism that predictions would not be sufficiently accurate are being replaced by optimism because errors of predictions are proving to be no greater than those of microbiological experiments. Modelling is set to play an important role in developing and maintaining a safe and wholesome food supply.