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

Isothermal heat-resistance studies were carried out on two toxin-producing Bacillus cereus strains (AVZ421 and AVTZ415) isolated from foods. Experimen tal data were analysed using the traditional Bigelow first-order kinetic mo del and the Weibull distribution model. Semilogarithmic survival curves sho wed an initial curvature that was more pronounced in the case of the psychr otrophic strain AVTZ415. Regression curves were obtained by means of the tr aditional Bigelow first-order model and the D values were calculated. Corre lation coefficients ranged from 0.983 to 0.989 for the AVZ421 strain and fr om 0.953 to 0.980 for the AVTZ415 strain. When the Weibull function was app lied to experimental data, a good description of the survivor microorganism s was obtained for the two strains considered. Using coefficients describin g the survival function, an average of the organism's heat resistance or se nsitivity, 'tc', at each temperature was estimated. Accuracy factors were o btained for experimental and calculated survivors as predicted by means of the Weibull or the Bigelow model. Results indicated that the accuracy facto r 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 degrees C, respectively. (C ) 1999 Elsevier Science Ltd. All rights reserved.