Submitted to: Letters in Applied Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/1/2003
Publication Date: 8/1/2003
Citation: Juneja, V.K. 2003. A comparative heat inactivation study of indigenous microflora in beef with that of listeria monocytogenes, salmonella serotypes and escherichia coli o157:h7. Letters in Applied Microbiology. 37:292-298 Interpretive Summary: The need for better control of foodborne pathogens has been of paramount importance in recent years. Heat inactivation of foodborne pathogens is one of the fundamentally important strategies to assure microbiological safety of cooked foods. Undercooked meat and meat products are commonly implicated as transmission vehicles in food poisoning outbreaks. We demonstrated that the heat treatment employed for the destruction of normal indigenous microflora in beef will be adequate to ensure safety against L. monocytogenes, E. coli O157:H7 and Salmonella in contaminated beef. This information will be of immediate use to consumers and to the food industry in judging safety based on the reduction of indigenous microflora in beef.
Technical Abstract: Thermal inactivation of a mixture of five strains of Listeria monocytogenes, four strains of Escherichia coli O157:H7 and eight serotypes of Salmonella was compared to that of indigenous microflora in 75% lean ground beef. Inoculated meat was packaged in bags that were completely immersed in a circulating water bath and held at 55, 57.5, and 60°C for predetermined lengths of time. The surviving cell population was enumerated by spiral plating heat-treated samples onto tryptic soy agar supplemented with 0.6% yeast extract and 1% sodium pyruvate. The D-values, as determined by linear regression, in beef were 77.49, 21.9, and 10.66 min at 55, 57.5, and 60°C, respectively, for indigenous microflora (z = 5.81°C). When either of the 3 pathogens were heated in beef, their calculated D-values were significantly lower (p < 0.05) than those of the indigenous microflora at all temperatures. The slope of the thermal death time curve for L. monocytogenes, E. coli O157:H7 and indigenous microflora were similar. Using a model for non-linear survival curves, the D - values of the major population (D1) at all temperatures for L. monocytogenes were significantly higher (p < 0.05) compared to those for Salmonella serotypes,E. coli O157:H7 or the indigenous microflora. However, higher recovery of a sub-population of the indigenous microflora in beef exposed to heating at 55, 57.5, or 60°C resulted in significantly higher (p < 0.05) D - values of the sub-population (D2) at all three temperatures, compared to those of the three pathogens at the same test temperatures. The results of this study will assist the retail food industry in designing acceptance limits on critical control points that ensure safety against L. monocytogenes, E. coli O157:H7 and Salmonella in cooked ground beef.