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 br ain 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 CO, level increased, and as pH and temperature decreased. Growth over a 30-day period was observe d 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 mo dels, the Gompertz and Baranyi equations, were compared for their abil ity to describe the growth of L. monocytogenes. In general, the Gomper tz model predicted both longer lag and shorter generation times, compa red to the Baranyi model. The Baranyi model appeared to fit the overal l data better than the Gompertz model. However, these differences were often small. Response surface models were developed for predicting th e effects and interactions of the three independent variables on the g rowth and/or survival of L. monocytogenes in the different modified at mospheres. Results demonstrate the importance of strict temperature co ntrol for maintaining the advantages of food shelf life extension in e nriched 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 orga nism may be a concern.