Risk of Bacillus cereus contamination in cooked rice

Abstract

Rice is prone to contamination with Bacillus cereus which causes food poisoning. The aim of this study was to investigate the presence of Bacillus cereus in cooked and uncooked rice. A total of forty samples of rice were collected from local supermarkets and tested before and after cooking for the presence of B. cereus. Half of the uncooked rice samples were B. cereus positive. In contrast B. cereus was not detected in the cooked samples when they were immediately examined for the presence of B. cereus. Storing the cooked sample at room temperature (25 °C) for twelve hours, however, gave the spores the chance to grow, and two samples showed bacterial growth higher than 1×10³ Cfu/g. The D-value of B. cereus ATCC 14579 spores was found to be 2.7, 1.55, 1.35, 1.2 and 0.6 min at 80, 85, 90, 95, and 100 °C respectively. The Z-value was 9 °C. The level of bacterial growth was below the limits but it was sufficient to suggest that cooked rice should be routinely checked for B. cereus to control bacterial contamination and reheating should reach 80 °C to insure the safety.

Keywords:
Bacillus cereus; D-value; Z-value; cooked rice; uncooked rice; food poisoning; food safety