Effect of lactic acid bacteria on extention of shelf life and growth of Listeria monocytogenes in beef steaks stored in CO2-rich atmosphere

Beef steaks were inoculated with one or other of two protective strains of lactic acid bacteria (bacteriocinogenic Lactobacillus sakei CTC 372 or the uncharacterized Lactobacillus CTC 711), and stored under modified atmospheres (20-40% CO2). Inoculation of meat with LAB inhibited growth of the spoilage bacteria. Neither CO2 in the pack atmosphere or inoculation with protective strains, nor a combination of both, affected formation of metmyoglobin or the development of off-odours. The formation of metmyoglobin in meat pigments and the sensory odour scores were compatible to those of fresh meat which had not undergone either oxidative deterioration or microbial spoilage. Listeria monocytogenes was inhibited in broth by meat surface microbiota containing the protective strains. With initial numbers of 5.6 log cfu mL(-1), after 7 days incubation at 3 degrees C, L. monocytogenes were recovered at log mean numbers of 2.8 log cfu mL(-1) when no protective strain was present. At 8 degrees C, the numbers of L. monocytogenes were reduced by about 2.5 or 1.5 log mL(-1) in the presence of Lb. sakei CTC 372 or Lb. CTC 711, respectively. At 25 degrees C, the numbers of L. monocytogenes recovered from broth containing either protective strain were about 5 log lower than the numbers recovered from broth containing L. monocytogenes only.