Abstract
We studied the change of aerobic bacterial number and the behavior of Bacillus cereus during the process of vacuum cooking to evaluate the safety of this cooking method. Sliced raw beef was used as an experimental specimen, which was wrapped vacuously before the cooking. Aerobic bacterial number, coliform group and B. cereus were examined in the specimen without any inoculation, and the behavior of B. cereus was investigated in vegetative cell- and spore-inoculated specimens. Specimens were examined before the cooking, after the first heating (either at 58°C for 40 min, 68°C for 40 min, or 80°C for 15 min), and then following re-heating at 80°C for 10 min. 2.8×104 cfu/g aerobic bacteria were detected before the cooking; this number decreased to 5.4×102 cfu/g after the first heating at 58°C for 40 min. Aerobic bacteria that survived this stage died out completely after the re-heating. On the other hand, no aerobic bacteria were seen following either of the other two initial heating treatments. Furthermore, coliform groups and B. cereus were not detected at the beginning of the experiment. Vegetative cells (4.0×104 cfu/g) completely disappeared after the first heating process, regardless of the conditions. Although spores (3.2×102 cfu/g) survived slightly after every initial heating treatment, they disappeared completely after the re-heating. The present results indicate that food subjected to vacuum cooking seems to be safe as long as the re-heating process functions appropriately. In other words, the re-heating process is necessary in order to secure the safety of this cooking method.
