Predictive model for the combined effect of temperature, pH, sodium chloride, and sodium pyrophosphate on the heat resistance of Escherichia coli O157 : H7

The effects and interactions of heating temperature (55 - 62.5C), pH (4 - 8 ), NaCl (0 - 6%, w/v), and sodium pyrophosphate (0 - 0.3%, w/v) on the heat resistance of a four strain mixture of Escherichia coli O157:H7 in beef gr avy were examined. Thermal death times were determined using a submerged co il heating apparatus. The recovery medium was plate count agar supplemented with 1% sodium pyruvate. Decimal reduction times (D-values) were calculate d by fitting a survival model to the data with a curve fitting program. The D-values were analyzed by second order response surface regression for tem perature, pH, NaCl and sodium pyrophosphate levels. The four variables inte racted to affect the inactivation of the pathogen. Thermal resistance of E. coli O157:H7 can be lowered by combining these intrinsic factors. A mathem atical model describing the combined effect of temperature, pH, NaCl and so dium pyrophosphate levels on the thermal inactivation of E. coli O157:H7 wa s developed. The model can predict D-values for any combinations of tempera ture, pH, NaCl and sodium pyrophosphate that are within the range of those tested.