PREDICTIVE MODELING OF PSYCHROTROPHIC BACILLUS-CEREUS

Response surface analysis was used to determine the effects and interactions of water activity (0.965 to 0.995), pH (5.8 to 8.0), temperature (6 to 38-degrees-C), glucose concentration (0 to 1.8%), and starch concentration (0 to 0.625%) on the growth of and toxin production by a psychrotrophic strain of Bacillus cereus in brain heart infusion broth. Growth was measured by monitoring optical density and plate counts, toxin production was assayed by an immunological method (BCET-RPLA toxin assay) and cytotoxicity with Vero and HEp-2 cells. Regressions were performed using response surface techniques, on Growth, LnGrowth, RPLA, LnRPLA, Vero, LnVero, and HEp-2; quadratic predictive equations for growth and toxin production were obtained. The results indicate the factors that had the greatest influence on both growth and toxin production were water activity and temperature. Predicted values obtained from the model were in good agreement with experimental values.