EVALUATION OF BACILLUS CEREUS GROWTH IN COOKED RICE

Abstract

The present study aimed to evaluate the dependence of growth dynamics of toxigenic B. cereus on rice type, inoculum type, storage time, and temperature using appropriate mathematical models. Samples of cooked white (milled) and brown (husked) rice inoculated with vegetative cell/spore suspension of B. cereus were stored for 48 h at 4 °C (correct storage) and 24 °C (inappropriate storage method). No growth of B. cereus was observed during 48 hours of storage at 4 °C and was characterised by a linear model. To assess the growth of B. cereus in the cooked rice stored at 24 °C, the Baranyi-Roberts, Gompertz and Buchanan mathematical models were used. The Gompertz model characterized the growth of B. cereus best. The type of rice and the type of inoculum did not have a significant effect on the bacterial growth. After 48 h of storage at 24°C, the B. cereus counts were in the range of 8-9 log cfu.g-1, critical value of 5 log cfu.g-1 was reached in less than 10 hours of storage. The study results indicate that cooked rice stored at 24 °C quickly becomes a health risk for consumers due to the rapid multiplication of B. cereus within a few hours. In conclusion, it is crucial to cool cooked rice immediately to 4 °C if it is not to be consumed right after cooking.