Estimation of Bacteria in Spoiled Cooked Rice

Abstract

　Spoilage of cooked rice occurred as a result of heat insulation. The cooked rice had an off-flavor that was caused by spoilage. This phenomenon is thought to be caused by microorganisms. Therefore, in this study, we attempted to isolate the contaminating microorganisms from cooked rice and identify them by using polymerase chain reaction (PCR) and PCR-denaturing gradient gel electrophoresis (DGGE). No microorganisms were detected in normal cooked rice; however, microorganisms were detected at 4.6×10⁶ cfu/g in rice spoiled by 72h of heat insulation. The isolates were able to grow at 60～65℃ on the cooked rice, and they produced an off-flavor. Based on phylogenetic analysis, the isolates were identified as members of the genus Geobacillus, and were closely related to Geobacillus thermoleovorans. Contaminating microorganisms in the cooked rice were identified by PCR using bacterial universal primers and G. thermoleovorans was only detected using PCR-DGGE. These results suggest that G. thermoleovorans was the contaminating microorganism in the spoiled cooked rice and produced the off-flavor.