Purpose: This study developed a dynamic model to predict the fates of Listeria monocytogenes in Nappa cabbage kimchi during fermentation under changing temperatures.
Methods: A mixture of L. monocytogenes strains NCCP10805, NCCP10806, NCCP10807, NCCP10808, NCCP10809, NCCP10810, NCCP10811, NCCP10920, and NCCP10943 was inoculated into Nappa cabbage kimchi at 4 log CFU/g. They were then incubated at 4°C (14 days), 15°C (2 days), and 25°C (1.5 days). L. monocytogenes and lactic acid bacteria cell counts were enumerated on PALCAM, and de Man, Rogosa and Sharpe agar, respectively. The microbiological data were fitted to the Baranyi model to estimate the kinetic parameters such as growth rate or death rate (log CFU/g/h), and lag phase duration (LPD; h) or shoulder period (h). The kinetic parameters were then fitted to a polynomial model. A dynamic model was eventually developed, and root mean square error (RMSE) was calculated to evaluate the model performance.
Results: L. monocytogenes growth was observed at 15°C and 25°C for cabbage kimchi, and the bacterial cell counts decreased (P<0.05) as lactic acid bacterial cell counts increased. Growth rate and death rate values from the Baranyi model were increased (P<0.05), but LPD or shoulder period were decreased (P<0.05) as storage temperature increased. A polynomial model then described well the effect of temperature on kinetic parameters, and a dynamic model was eventually developed to describe the fate of L. monocytogenes under changing temperature. RMSE suggested that the developed models had a good performance.
Significance: These results indicate that the developed models should be useful in predicting the fates of L. monocytogenes in Nappa cabbage kimchi fermentation at changing temperatures.