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

Inglés. 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 3ºC, L. monocytogenes were recovered at log mean numbers of 2.8 log cfu mL-1 when no protective strain was present. At 8ºC, 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 25ºC, 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.

Portugués. Fatias de carne bovina foram inoculadas com uma de duas bactérias láticas protetoras (Lactobacillus sakei CTC 372 bacteriocinogênica e Lactobacillus CTC 711 não caracterizado) e armazenadas em atmosfera modificada (20-40% CO2). A inoculação da carne com bactérias láticas protetoras inibiu a multiplicação de bactérias deteriorantes. O CO2 da atmosfera e/ou a presença de bactérias láticas não causou a formação de metmioglobina ou de odores indesejáveis. A formação de metmioglobina e as características sensoriais foram equivalentes às apresentadas por carne fresca não deteriorada e não submetida a tratamento. A multiplicação de Listeria monocytogenes em caldo foi inibida por bactérias isoladas da superfície das carnes inoculadas com as bactérias láticas. Após 7 dias a 3ºC, a contagem inicial de L. monocytogenes de 5.6 log UFC.mL-1 caiu para 2.8 log UFC.mL-1 na ausência de bactéria lática protetora. A 8ºC, as contagens de L. monocytogenes foram reduzidas em 2.5 ou 1.5 log na presença de Lb. sakei CTC 372 ou Lb. CTC 711, respectivamente. A 25ºC, as contagens de L. monocytogenes no caldo contendo uma das bactérias láticas protetoras foram 5 log mais baixas do que nos caldos contendo L. monocytogenes somente.