Purpose: Therefore, the objective of this study was to develop a predictive model to describe the kinetic behavior of E. coli in Mozzarella and Cheddar slice cheeses under constant and dynamic temperature conditions.
Methods: A five-strain mixture of E. coli was inoculated on Mozzarella slice and Cheddar slice cheeses at 3-4 log CFU/g, and the inoculated samples were aerobically stored at 4-30°C for 24-1,320 h. Total bacteria and E. coli cell counts were then enumerated on tryptic soy agar and MacConkey sorbitol agar, respectively. The Baranyi model was fitted to the growth data of E. coli to calculate maximum specific growth rate (µmax; log CFU/g/h), lag phase duration (LPD; h), lower asymptote (log CFU/g), and upper asymptote (log CFU/g). The square root model or a polynomial equation was fitted to the kinetic parameters to describe the effect of storage temperature on the kinetic parameters. Dynamic models were also developed to describe kinetic behavior of E. coli at dynamic temperature. The performance of the developed model was evaluated by root mean square error (RMSE).
Results: The µmax values increased (P < 0.05), but LPD values decreased as temperature increased. At 4°C, E. coli cell growth was not observed for both cheeses. µmax and LPD values were different between Mozzarella cheese (µmax: 0.01-0.33 log CFU/g/h; LPD: 1.79-30.44 h) and Cheddar cheese (µmax: 0.00-0.28 log CFU/g/h; LPD: 6.08-768.00 h). For Mozzarella cheese, E. coli grew at 10-30°C with µmax of 0.01-0.33 log CFU/g/h, but E. coli grew at 15-30°C with µmax of 0.03-0.28 log CFU/g/h in Cheddar cheese. In addition, developed dynamic models described appropriately kinetic behavior of E. coli. RMSE(0.176-0.337) indicated that the developed models were appropriate.
Significance: The developed models in this study could be useful in describing the kinetic behavior of E. coli in Mozzarella and Cheddar cheeses under constant and dynamic temperature.