Validation of Predictive Mathematical Models Describing the Growth of Escherichia coli O157:H7 in Raw Ground Beef.

The growth of Escherichia coli O157:H7 in raw ground beef was investigated at 12°C, 20°C, and 35°C at pH 5.7 (unadjusted) and adjusted to pH 6.3 to 6.4. These growth data were fitted to the Gompertz equation and the resulting growth kinetics were compared with predictions from the U.S. Department of Agriculture Pathogen Modeling Program. Close agreement with the model was obtained at pH 5.7, but at pH 6.4, growth was more rapid than predicted. The U.S. Department of Agriculture Food Safety and Inspection Service has used this predictive model for developing proposed regulations on time-temperature requirements for carcass cooling. As there may be considerable differences in the microenvironment of raw ground beef and a beef carcass, the validity of using predictive models for estimating growth rates on a carcass should be determined by performing growth studies on carcass surfaces.