RESPONSE SURFACE MODEL FOR EFFECTS OF TEMPERATURE, WATER ACTIVITY AND pH ON GERMINATION OF BACILLUS CEREUS SPORES

A response surface model was developed for effects of temperature (20 to 40C), pH (4.5 to 6.5) and water activity (a_w) (0.94 to 0.99) on germination of Bacillus cereus ATCC 11778 spores. Germination depended, to varying extents, on the interactions among the independent variables and complexity of the medium. In particular it was affected (P < 0.05) by interactions of a_w with temperature and pH and by temperature in its quadratic term. The model was validated against data not used in its development. Mean absolute relative error of predictions (model accuracy) was 22.8% in model systems and 10.17% in real systems. Bias factors were 0.887 and 0.922 for model and real systems, respectively. Results indicated that the model developed was "fail safe" and provided reliable predictions of germination of B. cereus.