Modelling Yersinia enterocolitica inactivation in coculture experiments with Lactobacillus sakei as based on pH and lactic acid profiles.

In food processing and preservation technology, models describing microbial proliferation in food products are a helpful tool to predict the microbial food safety and shelf life. In general, the available models consider microorganisms in pure culture. Thus, microbial interactions are ignored, which may lead to a discrepancy between model predictions and the actual microbial evolution, particularly for fermented and minimally processed food products in which a background flora is often present. In this study, the lactic acid mediated negative microbial interaction between the lactic acid bacterium Lactobacillus sakei and the psychrotrophic food pathogen Yersinia enterocolitica was examined. A model describing the lactic acid induced inhibition (i.e., early induction of the stationary phase) of the pathogen [Vereecken, K.M., Devlieghere, F., Bockstaele, A., Debevere, J., Van Impe, J.F., 2003. A model for lactic acid induced inhibition of Yersinia enterocolitica in mono- and coculture with Lactobacillus sakei. Food Microbiology 20, 701-713.] was extended to describe the subsequent inactivation (i.e., decrease of the cell concentration to values below the detection limit). In the development of a suitable model structure to describe the inactivation process, critical points in the variation of the specific evolution rate mu [1/h] with the dynamic (time-varying) pH and undissociated lactic acid profiles were taken into account. Thus, biological knowledge, namely, both pH and undissociated lactic acid have an influence on the microbial evolution, was incorporated. The extended model was carefully validated on new data. As a result, the newly developed model is able to accurately predict the growth, inhibition and subsequent inactivation of Y. enterocolitica in coculture as based on the dynamic pH and lactic acid profiles of the medium.

Predicting inhibition and inactivation of Yersinia enterocolitica through lactic acid production by Lactobacillus sakei.

In food technology, there is a need for models taking into account the interactions between microorganisms, in order to correctly predict the safety and shelf life of food products. When leaving these interactions out of consideration, a discrepancy between the model prediction and the actual microbial evolution may occur for certain types of food products. In this study, a model describing the inhibition of the pathogenic Yersinia enterocolitica in mono- and coculture with Lactobacillus sakei was extended to describe also the subsequent inactivation of Y. enterocolitica. During the development of a suitable model structure to describe the inactivation process, biological knowledge about this process was incorporated. The extended model was able to predict evolution of Y. enterocolitica in coculture as well as in monoculture.