Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/13/2005
Publication Date: 7/15/2005
Citation: Hwang, C. 2005. The effect of mayonnaise ph and storage temperature on the behavior of listeria monocytogenes in ham salad and potato salad. Journal of Food Protection. v. 68. p. 1628-1637. Interpretive Summary: Deli salads have been identified to have a high relative risk of causing foodborne illness by Listeria monocytogenes. Therefore, there is a need to understand the behavior of this pathogen in deli salads of various formulations stored under refrigerated temperature and temperature abuse condtions. To produce mathmatic models to describe the behavior of L. monocytogenes in deli salads as affected by the salad dressing pH (mayonnaise, pH 3.8-4.6) and storage temperature (4°, 8°, and 12°C), L. monocytogenes was studied in ham salad and potato salad. At each storage temperature, L. monocytogenes was able to grow in ham salad, but not in potato salad. The growth or inactivation of L. monocytogenes in ham salad or potato salad was significantly affected by the storage temperature, with a less effect from the mayonnaise pH. Mathematical models that described the growth of L. monocytogenes in ham salad and potato salad of various formulations at storage temperatures of 4°-12°C were developed. The models can be used by food processors, distributors and retailers to determine product formulation and storage conditions that control the growth of L. monocytogenes in ham salad and potato salad.
Technical Abstract: Ham salad and potato salad have been identified to have a relatively high incidence of contamination by Listeria monocytogenes. The objectives of this study were to examine and model the behavior of this pathogen in ham salad and potato salad as affected by the pH of salad dressing (mayonnaise) and storage temperature. Cooked ham or potato was inoculated with an 8-strain cocktail of L. monocytogenes, and mixed with mayonnaise of pH 3.8, 4.2, or 4.6. The cell counts of L. monocytogenes in the salads during storage at 4°, 8°, or 12°C were enumerated, and the cell counts were used to model the behaviors of L. monocytogenes in ham salad or potato salad. At each of the storage temperatures, L. monocytogenes was able to grow in ham salad. However, L. monocytogenes was inactivated in potato salad. The growth rate (GR, log10 cfu/h) of L. monocytogenes in ham salad and the inactivation of L. monocytogenes in potato salad increased as the storage temperature increased. In general, a longer lag phase duration (LPD, h) of L. monocytogenes in both ham salad and potato salad was observed at lower storage temperatures. Mathematical models that described the GR and LPD of L. monocytogenes in ham salad or potato salad as a function of mayonnaise pH and storage temperature were developed. The GR and LPD of L. monocytogenes in ham salad were mainly affected by the storage temperature, whereas the GR and LPD in potato salad were mainly affected by the storage temperature and the pH of the mayonnaise, respectively. A model performance analysis showed that the LPD and GR models for ham salad or potato salad present a worst case scenario in estimating the growth or survival of L. monocytogenes in ham salad or potato salad formulated with mayonnaise pH of 3.8-4.6 and stored at 4°-12°C.