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A comparative heat inactivation study of indigenous microflora in beef with that of Listeria monocytogenes , Salmonella serotypes and Escherichia coli O157:H7
Author(s) -
Juneja Vijay K.
Publication year - 2003
Publication title -
letters in applied microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.698
H-Index - 110
eISSN - 1472-765X
pISSN - 0266-8254
DOI - 10.1046/j.1472-765x.2003.01393.x
Subject(s) - listeria monocytogenes , escherichia coli , serotype , microbiology and biotechnology , salmonella , bacteria , biology , listeria , enterobacteriaceae , escherichia , food science , biochemistry , gene , genetics
Aims: Thermal inactivation of a mixture of five strains of Listeria monocytogenes , four strains of Escherichia coli O157:H7 and eight serotypes of Salmonella were compared with that of indigenous microflora in 75% lean ground beef. Methods and Results: 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 soya agar supplemented with 0·6% yeast extract and 1% sodium pyruvate. D ‐values, 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 three pathogens were heated in beef, their D ‐values calculated were significantly lower ( P < 0·05) than those of 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 survival model for nonlinear survival curves, the D 1 ‐values at all temperatures for L. monocytogenes were significantly higher ( P < 0·05) compared with those for Salmonella serotypes, E. coli O157:H7 or indigenous microflora. However, higher recovery of a subpopulation of the indigenous microflora in beef exposed to heating at 55, 57·5 or 60°C resulted in significantly higher ( P < 0·05) D 2 ‐values at all three temperatures, compared with those of the three pathogens at the same test temperatures. Conclusions: If the thermal process is designed to ensure destruction of indigenous microbial flora, it should also provide an adequate degree of protection against L. monocytogenes , Salmonella serotypes or E. coli O157:H7. Significance and Impact of the Study: The results of this study will assist the retail food industry in designing acceptance limits on critical control points that ensure safety, without introducing pathogens in a retail food environment, against L. monocytogenes , E. coli O157:H7 and Salmonella in cooked ground beef.