1994 Volume 11 Issue 1 Pages 29-33
Listeria monocytogenes (L. m. ) in shredded cheese was examined for its growth behavior during cold storage and cooking. During storage at 5°C, the concentration after inoculation decreased up to day 20 and thereafter increased. On day 77, the concentration was recovered to almost the same level as that at the time of inoculation, in shredded cheese inoculated with 104 or 106/g L.m. and increased by 1-2 orders in shredded cheese inoculated with 101/g L .m. . Also during storage at 10°, the inoculated L.m. decreased up to day 20 and thereafter increased, each bacterial concentration increased by 1-4 orders. Organoleptically, fungigenesis occurred from days 20 and 15 at 5° and 10°, respectively. The number of bacteria surviving in the pizza inoculated with 106/g L.m. was 3.6-23/100 g after heating at 200°C for 5 min, while heating at 250°C for 5 min caused the death of all the inoculated bacteria, that is 106/g. The change of the temperature at the center of the pizza while cooking tended to decrease with the increases in the temperature of storage and in the volume of ingredients, and these changes were also macroscopically recognizable.
The above findings suggested that L. m. in shredded cheese dose not proliferate during the allowable period of storage before consumption and becomes extinct with general methods of cooking.
