Title: The influence of acid stress on the growth of Listeria monocytogenes and escherichia coli O157:H7 on cooked ham Authors
Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 17, 2013
Publication Date: N/A
Interpretive Summary: Acid treatment is increasingly being used to decontaminate meat products. L. monocytogenes and E. coli O157:H7 are main pathogens of concern in meat products and were reported to survive the acid treatments. This study examined the food safety implication when acid-stressed L. monocytogenes and E. coli O157:H7 re-contaminated cooked ham products. Results showed that acid-stress reduced the growth of L. monocytogenes and E. coli O157:H7 on ham. However, a substantial food safety improvement was only for ham treated with high acid concentrations (pH is less than 3) and stored at refrigerated temperatures. For L. monocytogenes and E. coli O157:H7 sujbected to mild acid treatements, they remained capable of growing on ham at refrigerated and abuse temperatures.
Technical Abstract: Acid solutions are increasingly being used for meat surface decontamination. Microbial cells that survive acid treatments may be subjected to acid stress and exhibit different growth characteristics from the non-stressed cells. The objective of this study was to determine the growth behaviors of acid-stressed L. monocytogenes and E. coli O157:H7 on cooked ham. Cells of a multiple-strain mixture of L. monocytogenes or E. coli O157:H7 were exposed to acid stress in HCl solutions of pH 3, 4 and 5 and distillated water (no stress) at room temperature for 24 h. The stressed and non-stressed L. monocytogenes and E. coli O157:H7 were inoculated onto cooked ham and stored at 4 and 8 degrees Celsius and at 10 and 12 degrees Celsius, respectively. Populations of both microorganisms on ham were enumerated during storage, and the lag phase durations (LPD, h) and growth rate (GR, log CFU/h) were determined. Compared to no-stress treatment, the acid-stress treatments of pH 5, 4 and 3 reduced the populations of L. monocytogenes and E. coli O157:H7 by 1.2-3.1 and 0.6-2.4 log CFU/ml, respectively, indicating an increased acid stress to both microorganisms at lower pH. L. monocytogenes subjected to pH 3 and pH 4 stresses exhibited extended LPDs and reduced GRs on cooked ham, whereas only E. coli O157:H7 that was subjected to pH 3 stress exhibited extended LPDs and reduced GRs. The growth of stressed L. monocytogenes was more readily reduced by acid stress than that of E. coli O157:H7. Although acid-stressed L. monocytogenes or E. coli O157:H7 showed reduce growth ability on ham, both microorganisms remained capable of growing on ham at refrigerated and abuse temperatures. This study points to the need of proper temperature control for meat products treated with acid deconatamination.