보온 밥솥에서 보관 중인 밥의 품질을 개선하기 위하여 기존의 밥솥보온 온도인 $75^{circ}C$에 비하여 $45{sim}65^{circ}C$로 반복 순환시켜 낮게 유지시켰다. 이렇게 낮게 유지시켰을 때 미생물의 오염, 밥의 변색, 환원당의 생성에 관하여 연구를 진행하였다. B. cereus와 B. subtilis는 $45{sim}65^{circ}C$와 $75^{circ}C$에서 모두 사멸되었다. E. coli는 $75^{circ}C$에서는 약간의 colony forming unit의 증가가 있었으나 $45{sim}65^{circ}C$ 반복 순환 온도에서는 증식이 거의 없었다. CIE 변수인 황변도(${Delta}b$) 값의 변화는 3일간의 저장에서 $45{sim}65^{circ}C$에서는 2.18이 $75^{circ}C$에서는 9.12 증가 되었다. 환원당의 경우 미생물의 증식이 없었던 $45{sim}65^{circ}C$와 $75^{circ}C$에서 모두 생성되지 않았다. 결론적으로 밥의 $45{sim}65^{circ}C$에서 저장은 기존의 $75^{circ}C$에 비하여 미생물의 증식을 막고, 3일간의 저장에서 4.2배의 갈변을 감소시켜 품질의 저하를 방지하는데 우수하였다.
To improve the quality of boiled rice after storage in rice cookers, temperature was controlled at a lowered condition ($45{sim}65^{circ}C$ repeated temperature cycling), compared to the present commercial rice cookers ($75^{circ}C$). The effect of lowered temperature cycling on the microbial growth, color of rice, and reducing sugar production was measured. The bacteria Bacillus cereus and B. subtilis were killed at $75^{circ}C$ and $45{sim}65^{circ}C$ cycling. The temperature cycling at $45{sim}65^{circ}C$ prevented an increase in colony forming unit of E. coli more than the steady temperature at $75^{circ}C$. Browning during storage was significantly decreased at $45{sim}65^{circ}C$ cycling, compared to $75^{circ}C$. The yellowness increase (${Delta}b$ value of CIE parameters of the colorimeter) after the 3-day storage was 2.18 at $45{sim}65^{circ}C$ cycling whereas 9.12 at $75^{circ}C$. Reducing sugar was not produced at $75^{circ}C$ and $45{sim}65^{circ}C$ cycling but produced at $30^{circ}C$ because of the microbial growth. In conclusion, the temperature cycling at $45{sim}65^{circ}C$ can improve the quality of stored boiled rice by decreasing the browning and inhibiting the microbial growth.
