Purpose: The objective of this study was to develop a kinetic model to describe the kinetic behavior of S. aureuson processed cheeses.
Methods: Mozzarella and cheddar slice cheeses from Company A and B, and gouda slice cheese from Company A were inoculated with a five-strain mixture of S. aureus at 3 log CFU/g. The samples were stored at 4 (1440 h), 15 (288 h), 25 (72 h) and 30°C (48 h). Total bacterial and S. aureus cell counts were enumerated on tryptic soy agar and mannitol salt agar, respectively. The growth data of S. aureus 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 further analyzed by the square root model as a function of temperature. The model performance was validated with observed data, and root mean square error (RMSE) was calculated.
Results: At 4 and 15°C, S. aureus cell growth was not observed for all processed cheeses. However, the growth of S. aureus on mozzarella, cheddar, and gouda slice cheeses was observed at 25 and 30°C. The µmax values increased, but LPDs decreased as storage temperature increased. No differences of the µmax and LPD values were not observed between mozzarella and cheddar slice cheeses, but the S. aureus had lower (P < 0.05) growth on gouda sliced cheese than those of mozzarella and cheddar sliced cheeses. In addition, the developed models showed acceptable performance (RMSE=0.413-0.750).
Significance: This result indicates that the developed model should be useful in predicting S. aureus growth in mozzarella, cheddar and gouda sliced cheeses.