EXPANDED RESPONSE-SURFACE MODEL FOR PREDICTING THE EFFECTS OF TEMPERATURES, PH, SODIUM-CHLORIDE CONTENTS AND SODIUM-NITRITE CONCENTRATIONS ON THE GROWTH-RATE OF YERSINIA-ENTEROCOLITICA

The previously reported data set for the low temperature(5, 12 and 19 degrees C) of Yersinia enterocolitica was expanded to include higher abusive temperature (28, 37 and 42 degrees C). In addition to temperature, the data set included the effects and interactions of pH (4.5-8.5), sodium chloride (0.5-5%) and sodium nitrite (0-200 mu g ml(-1)) on the aerobic growth of Y. enterocolitica in brain heart infusion broth. Growth curves were modeled by fitting viable count data to the Gompertz equation. Quadratic models of natural logarithm transformations of the Gompertz B and M values and the derived values for lag phase durations and generation times were obtained using response surface analyses. Predictions based on the models for B and M values were comparable to predictions based on the derived values. These revised models provide an expanded means for rapidly estimating how the bacterium is likely to respond to any combination of the four variables within the specified ranges.