Title: Growth Kinetics of Listeria monocytogenes in Broth and Beef Frankfurters– Determination of Lag Phase Duration and Exponential Growth Rate under Isothermal Conditions Author
Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 26, 2008
Publication Date: May 1, 2008
Citation: Huang, L. 2008. Growth Kinetics of Listeria monocytogenes in Broth and Beef Frankfurters– Determination of Lag Phase Duration and Exponential Growth Rate under Isothermal Conditions. Journal of Food Science. 73(5):E235-E242. Interpretive Summary: Listeria monocytogenes is a pathogen that has caused foodborne illness outbreaks in the U.S. To protect the public from being harmed by this pathogen, it is necessary to know and characterize how it grows in foods. A new mathematical model has been developed to accurately describe and characterize different stages of the growth of Listeria monocytogenes in broth and beef frankfurters. This mathematical model can be used to provide more accurate estimation of the fate of Listeria monocytogenes in foods during storage and distribution, and therefore useful for assessing the risk of this microorganism.
Technical Abstract: The objective of this research was to develop a new kinetic model to describe the isothermal growth of microorganisms. The new model was tested with Listeria monocytogenes in broth and frankfurters, and compared with two commonly used models - Baranyi and modified Gompertz models. Bias factor (BF), accuracy factor (AF), and root mean square errors (RMSE) were used to evaluate the three models. Either in broth or in frankfurter samples, there are no significant differences in BF (about 1.0) and AF (1.02 – 1.04) among the three models. In broth, the mean RMSE of the new model was very close to that of the Baranyi model, but significantly lower than that of the modified Gompertz model. However, in frankfurters, there are no significant differences in the mean RMSE values among the three models. These results suggest that these models are equally capable of describing isothermal bacterial growth curves. Almost identical to the Baranyi model in the exponential and stationary phases, the new model has a more identifiable lag phase and also suggests that the bacteria population would increase exponentially until the population approaches to within 1~2 logs from the stationary phase. In general, there is no significant difference in the means of the lag phase duration and specific growth rate between the new and Baranyi models, but both are significantly lower than those determined from the modified Gompertz models. The model developed in this study is directly derived from the isothermal growth characteristics, and is more accurate in describing the kinetics of bacterial growth in foods.