FACTORS AFFECTING THE SUSCEPTIBILITY OF MEATBORNE PATHOGENS AND SPOILAGE BACTERIA TO ORGANIC-ACIDS

The bactericidal effects of lactic and acetic acids were assessed on artificially inoculated lean beef. The test bacteria included cold tolerant pathogens (Listeria monocytogenes, Yersinia enterocolitica), mesophilic pathogens (Salmonella typhimurium, Escherichia coli, Campylobacter jejuni and Staphylococcus aureus) and spoilage bacteria (Pseudomonas fragi and Brochothrix thermosphacta). Acid temperature (20-degrees-C, 55-degrees-C), acid concentration (1%, 3%) and initial numbers of contaminating bacteria (log CFU/cm2 of 3-6) were the variables studied. The bactericidal efficacy of organic acids was influenced by two- and three-way interactive effects that were often distinct for each organism. The magnitude of the reductions in bacterial numbers on acid-treated beef was similar with lactic and acetic acids. Bacterial numbers were maximally reduced with 3% acid at 55-degrees-C. The variations in the reductions in the numbers of bacteria on acid-treated beef were significantly affected by initial levels of bacterial contamination, but this effect followed no consistent pattern and varied with bacterial species. Of the pathogens tested, S. aureus was the most susceptible to acid (1.4 log cycle reduction) and S. typhimurium the least susceptible (0.4 log cycle reduction). The spoilage bacteria P. fragi (2.3 log cycle reduction) and B. thermosphacta (3.5 log cycle reduction) were more sensitive to the lethal effects of acid treatment than the pathogens.