Predictive modeling of the growth of Listeria monocytogenes in CO2 environments

The effects of pH (5.5, 6.5), temperature (4, 7 and 10 degrees C) and carbon dioxide (10, 30, 50, 70 and 90%) on the growth and/or survival of a five strain mixture of Listeria monocytogenes were examined in brain heart infusion broth. All three variables had a major influence on the growth characteristics of the organism. As expected, both the lag time and generation time increased as the CO2 level increased, and as pH and temperature decreased. Growth over a 30-day period was observed at all parameter combinations tested, except at pH 5.5, 4 degrees C in the presence of either 50, 70 or 90% carbon dioxide. Two primary models, the Gompertz and Baranyi equations, were compared for their ability to describe the growth of L. monocytogenes. In general, the Gompertz model predicted both longer lag and shorter generation times, compared to the Baranyi model. The Baranyi model appeared to fit the overall data better than the Gompertz model. However, these differences were often small. Response surface models were developed for predicting the effects and interactions of the three independent variables on the growth and/or survival of L. monocytogenes in the different modified atmospheres. Results demonstrate the importance of strict temperature control for maintaining the advantages of food shelf life extension in enriched carbon dioxide environments. The information obtained in this study could be used as a guide to manufacturers of modified-atmosphere packaged foods, especially when designing products in which this organism may be a concern.