VALIDATION OF PREDICTIVE MATHEMATICAL-MODELS DESCRIBING GROWTH OF STAPHYLOCOCCUS-AUREUS

An investigation was performed on the growth of Staphylococcus aureus in a commercially available, sterile, homogeneous food at 12 degrees C with 1.2 and 5.9% NaCl; at 25 degrees C with 10.4% NaCl; and at 20 an d 35 degrees C with 1.2, 5.3, 12.5, and 15.8% NaCl; over a pH range of 5.5 to 7.5. Growth data were fitted to the Gompertz equation and the resulting growth kinetics were compared with predictions from the Path ogen Modeling Program (PMP) and Food MicroModel (FMM). For the PMP, pr edicted lag-phase durations varied from 0.5 to 130 h longer than the o bserved values. In general, close agreement with growth rates was obta ined but there was a 10-fold difference in one case. For FMM, predicte d lag-phase durations ranged from 27 h shorter to 47 h longer than the observed values. Again, close agreement with growth rates was obtaine d, but in one case a fivefold difference was observed. In general, for the sterile foods used under the growth conditions tested, the models underestimated the growth of S. aureus. This implies that while the m odels can be used as a guide to indicate growth rates in foods they sh ould not be relied upon as the sole determinant of the product's safet y.