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 inte ractions of temperature (5, 12, 19-degrees-C), pH (4.5-8.5), sodium ch loride (0.5-5%) and sodium nitrite (0-200 mug/ml) on the aerobic growt h of Y. enterocolitica in brain heart infusion broth. Growth curves we re modeled by fitting plate count data to the Gompertz equation. Quadr atic models of natural logarithm transformations of the Gompertz B and M values and the derived values for lag phase durations and generatio n times were obtained using response surface analysis. Predictions bas ed on the models for B and M values were comparable to predictions bas ed on the derived values. These models provide a means for rapidly est imating how the bacterium is likely to respond to any combination of t he four variables within the specified ranges.