DIFFERENTIAL GROWTH OF LISTERIA-MONOCYTOGENES AT 4 AND 8-DEGREES-C - CONSEQUENCES FOR THE SHELF-LIFE OF CHILLED PRODUCTS

Growth rates and lag times of Listeria monocytogenes at 4 and 8 degree s C were compared in dairy products (milk, cream, and cheese), minced beef, and smoked salmon. Results showed that an increase in incubation temperature from 4 to 8 degrees C leads to a significant decrease in time required to reach a given bacterial population density. The decre ases were about 50% on cheese surfaces, 60 to 65% in milk and cream, a nd 75 to 80% in minced beef and smoked salmon. Consequences on the she lf life of chilled products are discussed on the basis of a simple and general linear relationship between the relative decrease in shelf Li fe and generation time. This relationship was experimentally highlight ed and theoretically demonstrated.