A comparison of the effects of E-beam irradiation and heat treatment on the variability of Bacillus cereus inactivation and lag phase duration of surviving cells.

The effects of electron beam irradiation and heat treatments on the variability of inactivation of Bacillus cereus spores (CECT 131/ATCC 10876) and of the lag phase of single surviving cells have been studied. In general, dispersion in the number of survivors increased as the stress became more intense. A polynomial relationship was derived between the coefficient of variation of the survivor number and the inactivation achieved. Heat treatments caused wider distributions than irradiation for the same substrate and for a similar degree of microbial inactivation. Increasing the intensity of the inactivation treatment lengthened the lag phase of survivors and increased its variability. Comparison of lag phases of heated and irradiated spores did not show any clear relationship. Heating did not affect the specific growth rate of surviving cells, whereas irradiation lowered the maximum specific growth rate in proportion to the dose applied. These results suggest that the shelf life of irradiated foods is longer than that of heated foods.