15A-14 |
Effect of heat-resistant lactic acid bacteria on Listeria innocua and Escherichia coli |
M. D. L. PÉREZ-CHABELA, R. García-Barrientos, E. Ponce-Alquicira, M. Signorini-Porchietto, and I. Guerrero-Legarreta. Dept. de Biotecnología, Univ. Autónoma Metropolitana-Iztapalapa, Av. Michoacán y la Purísima s/n Col. Vicentina, México, 09340, Mexico Lactic acid bacteria have used as bioprotective cultures in several meat products. These microorganisms are able to reduce pathogens and spoilage microflora. Research work has been also carried out to reduce spoilage microflora in emulsified products using heat-resistant lactic acid bacteria. These cultures must survive at processing temperatures of 70oC or more without considerably altering sensory characteristics. At the same time, bacteriocin-producing lactic acid bacteria could reduce proliferation of pathogens such as Listeria sp. or enterobacteria. The objective of this work was to study the ability to produce bacteriocins of four heat-resistant lactic strains and the extent these microorganisms can decrease the growth of Listeria inoccua and Escherichia coli. Lactobacillus alimentarius, L. minor, L. lactis and L. carnis or piscicola were preliminary tested for their ability to survive at temperatures above 70oC. They were also tested for bacteriocin production following the plate diffusion technique. The strains showing bacteriocin production were tested against Listeria inoccua and Escherichia coli by development of inhibition haloes in agar plates. These strain were tested in meat against the same target microorganisms, by inoculating them on beef previously to the lactic strain. L. alimentarius was better acidifier than L. piscicola, therefore had better control on enterobacteria than on L. Inoccua. Both lactic strains produced bactericins in agar plates, although they were not active against L. inoccua and E. coli. When grown in meat, the lactic strains also showed bacteriocin production. Use of heat-resistant lactic acid bacteria, can be a means to increase the shelf life of emulsified meat products. However, the tested strains were able to reduce enterobacteria due to acid production or substrate competition rather than to bactericin production. As meat acts as a protective environment for target microorganisms, bactericin activity was negligible.
Session 15A, Biotechnology
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