Application of a frequency distribution model to describe the thermal inactivation of two strains of Bacillus cereus

Abstract Isothermal heat-resistance studies were carried out on two toxin-producing Bacillus cereus strains (AVZ421 and AVTZ415) isolated from foods. Experimental data were analysed using the traditional Bigelow first-order kinetic model and the Weibull distribution model. Semilogarithmic survival curves showed an initial curvature that was more pronounced in the case of the psychrotrophic strain AVTZ415. Regression curves were obtained by means of the traditional Bigelow first-order model and the D values were calculated. Correlation coefficients ranged from 0.983 to 0.989 for the AVZ421 strain and from 0.953 to 0.980 for the AVTZ415 strain. When the Weibull function was applied to experimental data, a good description of the survivor microorganisms was obtained for the two strains considered. Using coefficients describing the survival function, an average of the organism's heat resistance or sensitivity, ‘tc’, at each temperature was estimated. Accuracy factors were obtained for experimental and calculated survivors as predicted by means of the Weibull or the Bigelow model. Results indicated that the accuracy factor was lower when the Weibull model was used (1.10 and 1.10) than when using the Bigelow model (1.20 and 1.30) at 95 and 85°C, respectively.