RESPONSE-SURFACE MODEL OF THE EFFECT OF PH, SODIUM-CHLORIDE AND SODIUM-NITRITE ON GROWTH OF YERSINIA-ENTEROCOLITICA AT LOW-TEMPERATURES

A fractional factorial design was used to measure the effects and interactions of temperature (5, 12, 19-degrees-C), pH (4.5-8.5), sodium chloride (0.5-5%) and sodium nitrite (0-200 mug/ml) on the aerobic growth of Y. enterocolitica in brain heart infusion broth. Growth curves were modeled by fitting plate 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 analysis. Predictions based on the models for B and M values were comparable to predictions based on the derived values. These models provide a means for rapidly estimating how the bacterium is likely to respond to any combination of the four variables within the specified ranges.