Comparison of predictive growth models for Bacillus cereus in cooked and fried rice during storage

Abstract

This study aimed to develop and compare growth models of Bacillus cereus in cooked and fried rice. A cocktail of B. cereus was inoculated into cooked and fried rice to obtain an initial concentration of ca. 2 log CFU g-1 and stored at 13, 30, 42, and 60oC. The cell concentration of B. cereus during storage were fitted to the primary models of Baranyi, Huang, and modified Gompertz. The maximum specific growth rates (µmax) were fitted to the Ratkowsky model, while the lag phase was fitted using the first-order polynomial model. There was no significant difference (p>0.05) in the µmax and lag phase of B. cereus in cooked rice or fried rice at 13 and 30oC. However, at 42oC the µmax in fried rice was significantly higher (p<0.05) and the lag phase was significantly longer (p<0.05) than those in cooked rice. No growth was observed at 60oC. The Baranyi model showed the best performance in fitting the µmax of B. cereus in cooked and fried rice. The validation study confirmed that the Ratkowsky and the first-order polynomial model could satisfactorily fit the µmax and the lag phase, respectively.  Modeling of B. cereus growth in cooked and fried rice can use the primary model of Baranyi fitted to the secondary model of Ratkowsky and first-order polynomial to predict the growth rate and lag phase, respectively. The model suggests that B. cereus grows significantly faster in fried rice at 42oC.