Comparison of the thermal inactivation of Bacillus subtilis spores in foods using the modified Weibull and Bigelow equations

The association of a modified Weibull model and Bigelow model was applied to the thermal inactivation of Bacillus subtilis spores heated in phosphate buffer, milk, kayu (a Japanese style rice porridge) and soy sauce as well. The inactivation kinetics presented a light downward concave profile, the acidic pH increased the efficiency of the heat treatment but on the opposite, lesser the water activity, weaker was the efficiency. The heat treatment kinetics observed in milk, soy sauce and kayu were greatly different from each other, while no large difference between sterilized whole milk, UHT whole milk, sterilized skim milk and UHT skim milk, were observed. The model established in buffer system allowed heat treatment in milk products to be simulated although it could not be employed to describe the inactivation of B. subtilis spores in soy sauce and kayu. For these two latter products, the food itself had to be introduced in the model as a parameter. Finally, this approach combining primary model (to simulate inactivation kinetics) and secondary model (to introduce temperature, pH, aw and food matrix effect) seemed available for food application, nevertheless validations of results such as challenge-tests, must be performed before it is put to routine use.