MODELING THE EFFECTIVENESS OF A NATURAL ANTIMICROBIAL ON SALMONELLA-ENTERITIDIS AS A FUNCTION OF CONCENTRATION, TEMPERATURE AND PH, USING CONDUCTANCE MEASUREMENTS

The growth of Salmonella enteritidis in a brain heart infusion medium was monitored using the traditional viable count method and by conduct ance measurements using a Rabit impedance instrument. Growth curves (l og(10) cfu ml(-1) vs time) at three different concentrations of oleuro pein (0, 0.2 and 0.8 %), pH values in the range of 5-8 and incubation temperatures from 22 to 42 degrees C were modelled using the Gompertz equation. A good correlation between the maximum growth rate from the viable count method and the maximum slope of the conductance curve fro m the impedance instrument was established. Based on this correlation, the maximum specific growth rate of Salm. enteritidis was modelled as a function of the oleuropein concentration, initial pH values and the incubation temperature with. a quadratic equation, using a new, large r dataset of growth measurements by conductance. The developed model w as validated by statistical comparison of predicted growth rates with growth rates determined by the viable count method, within the limits of the antimicrobial, pH and temperature domain.