Purpose: This study developed mathematical models to describe kinetic behavior of Escherichia coli in natural cheese during storage at constant and dynamic temperatures.
Methods: A five-strain mixture of E. coli was inoculated on 15 g of natural cheeses (Brie and Camembert cheeses). The samples were then aerobically stored at 4-30°C for 1-55 days under constant temperature and dynamic temperature (4-14°C). Total bacterial (tryptic soy agar) and E. coli (MacConkey sorbitol agar) cell counts were enumerated. The Baranyi model was fitted to the growth data of E. coli to estimate maximum specific growth rate (µmax) and lag phase duration (LPD). The µmax and LPD were further analyzed with the square root model and linear equation, respectively. Moreover, dynamic models were developed with changing temperature profile. Subsequently, the performance of the developed models was evaluated by the root mean square error (RMSE).
Results: Obvious growth of E. coli was observed in Brie and Camembert cheeses at 10-30°C. µmax increased (P < 0.05) up to 0.94 log CFU/g/h, but LPD decreased (P < 0.05) from 24.49 to 5.40h as temperature increased. No differences of µmax and LPD were observed between Brie (µmax: 0.03-0.94 log CFU/g/h; LPD: 5.40-20.13h) and Camembert cheeses (µmax: 0.03-1.03 log CFU/g/h; LPD: 5.92-24.49h). The secondary model properly described the effect of storage temperature on the parameters with high R2 (0.890-0.984). In addition, developed dynamic models were appropriate to describe the kinetic behavior of E. coli. The developed models showed appropriate prediction results with 0.218-0.264 of RMSE.
Significance: The developed mathematical models in this study should be useful in describing kinetic behavior of E. coli in natural cheeses under various storage conditions.