Effect of heat activation and inactivation conditions on germination and thermal resistance parameters of Bacillus cereus spores

The effect of isothermal and non-isothermal heat activation on germination and thermoresistance of two strains of Bacillus cereus spores was studied. Results indicated that the germination after isothermal activation was lower than after non-isothermal heating. The activation rate affected the z value, which increased with faster heating rates. For each temperature and inactivation rate, the non-isothermal activation at rate of 2°C/min resulted in larger D values (D90=4.70 min) than isothermal activation (D90=4.04 min). The two mathematical equations used to analyse non-isothermal data produced similar predicted D and z values, nevertheless the Hayakawa equation modified in this work for non-linear regression analysis, requires less computational effort.