Purpose: This study developed kinetic models to compare S. aureus growth on Brie and Camembert cheeses from two different companies.
Methods: Two fresh cheeses (Brie and Camembert) were purchased from two different companies (Company A and B), and 15 g of each fresh cheese was inoculated with 0.1 ml of a five-strain mixture of S. aureus to obtain 4 log CFU/g. The samples were then stored at 4, 10, 15, 25 and 30°C for 2-60 days. Total bacterial and S. aureus cell counts were enumerated on tryptic soy agar and mannitol salt agar, respectively. The growth data of S. aureus from Brie (company A and B) and Camembert (company A and B) cheeses were fitted to the Baranyi model to calculate maximum specific growth rate (µmax; log CFU/g/h) and lag phase duration (LPD; h). The kinetic parameters were fitted to the square root model as a function of temperature. To evaluate model performances, root mean square error (RMSE) was calculated.
Results: S. aureus growth was observed at 10, 15, 25 and 30°C for the cheese. µmax values were increased, but LPDs were decreased as storage temperature increased. No significant differences of µmax and LPD were observed among Brie and Camembert cheeses from two companies. The developed secondary model was acceptable (R2 = 0.918) to describe the effect of storage temperature on the kinetic parameters. In addition, the prediction of the developed model also showed acceptable performance (RMSE = 0.351).
Significance: The results indicate that the developed models in this study should be useful in describing kinetic behavior of S. aureus on Brie and Camembert cheeses.