Purpose: This study developed mathematical models to describe the kinetic behavior of NaCl-habituated and non-habituated S. aureus in sweet pumpkin salad.
Methods: The mixture of S. aureus strains (KACC10768, KACC10778, KACC11596, KACC13236, and NCCP10862) was habituated up to 9% NaCl and non-habituated. The inocula of NaCl-habituated and non-habituated S. aureus were inoculated in 5 g portions of sweet pumpkin salad. The samples were then aerobically stored at 10 (360 h), 15 (360 h), 20 (240 h), 25 (120 h), and 30°C (120 h). Total bacterial and S. aureus cell counts were enumerated on tryptic soy agar and mannitol salt agar, respectively. The growth data were fitted to the modified Gompertz model and the Baranyi model to calculate lag phase duration (LPD; h), maximum specific growth rate (μmax; log CFU/g/h), N0 (log CFU/g), and Nmax (log CFU/g). The kinetic parameters were then fitted to the Davey equation, a polynomial equation, and the square root model as a function of storage temperature. The model performance was also evaluated under constant (20 and 27°C) and dynamic condition, and root mean square error (RMSE) values were calculated.
Results: NaCl-habituated S. aureus cell counts were higher (P < 0.05) than those of non-habituated S. aureus at 15°C. S. aureus growth was observed at 15-30°C. For both primary models, LPDs were decreased, but μmax were increased as temperature increased. The developed secondary models were acceptable (R2: 0.898-0.981). The RMSEs were 0.55 and 0.88 for 20°C and 27°C, respectively. In addition, the prediction of S. aureus cell counts were close to the observed S. aureus cell counts under dynamic temperature.
Significance: The results indicate that the developed mathematical models should be useful in describing kinetic behavior of NaCl-habituated and non-habituated S. aureus cells in sweet pumpkin salad.