Effect of Lactic Acid Bacteria on Beef Steak Microbial Flora Stored Under Modified Atmosphere and on Listeria Monocytogenes in Broth Cultures

Beef steaks were inoculated with one or other of two protective strains of lactic acid bacteria, the bacte-riocinogenic Lactobacillus sakei CTC 372 or the uncharacterised Lactobacillus CTC 711. They were stored under modified atmospheres (20–40 % CO2). Inoculation of meat with both strains inhibited the growth of the spoilage bacteria. Neither CO2 in the pack atmosphere, 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 mono-cytogenes were inhibited in broth by meat surface microbiota containing either of the protective strains. With an initial population of 5.6 log cfu/mL, after 7 days incubation at 3 °C, Listeria monocytogenes were recovered at log mean population of 2.8 log cfu/mL when neither protective strain was present. At 8 °C, the population of Listeria monocytogenes recovered were reduced by about 2.5 or 1.5 log cfu/mL in the presence of Lactobacillus sakei CTC 372 or Lactobacillus CTC 711, respectively. At 25°C, the popu-lation of Listeria monocytogenes recovered from broth containing either protective strain were about 5 log cfu/mL less than the population recovered from broth containing Listeria monocytogenes only