Freezing and frozen storage on the survival of Listeria monocytogenes in different foods

An investigation was conducted on survival of Listeria monocytogenes inoculated into 5 different foods (chicken breast, beef hamburger, spinach, Mozzarella, cod fish) during freezing at 50 degrees C and extended storage (8-10 months) at -18 degrees C. Two strains of Listeria monocytogenes, Scott A and FIL/IDF strains, were examined. Only slight decreases in the viable population of Listeria monocytogenes (range 0.1-1.6 logs) over all foods were observed after 57 minutes at -50 degrees C. Cells of Listeria monocytogenes were more resistant to death and injury when they were inoculated in beef hamburger and chicken breast whereas they were less resistant in fish. A further reduction in viability of survival cells (up to 1.0 log) was detected after 240-300 days during storage at -180 degrees C. Of the two strains examined the one of human resistance during freezing at -50 degrees C, as well as storage at -18 degrees C, regardless of the kind of food.