PREDICTIVE MICROBIOLOGY IN A DYNAMIC ENVIRONMENT - A SYSTEM-THEORY APPROACH

The main factors influencing the microbial stability of chilled prepar ed food products for which there is an increased consumer interest - a re temperature, pH, and water activity. Unlike the pH and the water ac tivity, the temperature may vary extensively throughout the complete p roduction and distribution chain. The shelf life of this kind of foods is usually limited due to spoilage by common microorganisms, and the increased risk for food pathogens. In predicting the shelf life, mathe matical models are a powerful tool to increase the insight in the diff erent subprocesses and their interactions. However, the predictive val ue of the sigmoidal functions reported in the literature to describe a bacterial growth curve as an explicit function of time is only guaran teed at a constant temperature within the temperature range of microbi al growth. As a result, they are less appropriate in optimization stud ies of a whole production and distribution chain. In this paper a more general modeling approach, inspired by system theory concepts, is pre sented if for instance time varying temperature profiles are to be tak en into account. As a case study, we discuss a recently proposed dynam ic model to predict microbial growth and inactivation under time varyi ng temperature conditions from a system theory point of view. Further, the validity of this methodology is illustrated with experimental dat a of Brochothrix thermosphacta and Lactobacillus plantarum. Finally, w e propose some possible refinements of this model inspired by experime ntal results.