Aims: To evaluate a novel secondary model structure (Int J Food Microbiol 2008; 128: 67) that describes the effect of medium structure on the maximum specific growth rate (mu(max)) of Salmonella Typhimurium on the growth of S. Typhimurium, Listeria innocua, Lactococcus lactis and Listeria monocytogenes.
Methods and results: In the present study, the novel secondary model is validated for S. Typhimurium in more realistic media, namely, pasteurized milk and a cheese mimicking medium. The predictions were accurate. Next, the secondary model structure was evaluated in a two step and a global regression procedure on literature data. On the one hand, the growth of two other micro-organisms, namely L. innocua and L. lactis, in monoculture for varying gelatine concentrations was tested and on the other hand the growth rate of L. monocytogenes was fitted in a broth of which the viscosity was altered with polyvinylpyrrolidone. The model was able to describe the effect of increasing gelatine concentration or viscosity accurately.
Conclusions: The proposed secondary model structure is able to describe the effect of gelatine concentration on the mu(max) of the micro-organisms tested in this study.
Significance and impact of the study: In predictive microbiology, much attention has been paid to the effect of food structure on the mu(max) of bacteria. However, to the authors' knowledge, a lack of secondary models still exists to describe this effect. Although the proposed model is empirical, the model parameters have clear biological meaning. The predictive power of the model to describe the effect of food structure is clearly illustrated.