Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 23, 2004
Publication Date: July 14, 2005
Citation: Hwang, C., Tamplin, M.L. 2005. The influence of mayonnaise pH and storage temperature on the growth of Listeria monocytogenes in seafood salad. International Journal of Food Microbiology. v. 102. p. 277-285. Interpretive Summary: The majority of mathematical models to predict the growth of Listeria monocytogenes(LM)under varying environmental conditions of acidity, moisture and additives, have been developed in culture broth system models and have not been sufficiently validated for higher risk retail food products. To improve the utility of models for the food industry, the growth of LM was studied in a ready-to-eat seafood salad, as function of salad dressing acidity (mayonnaise, pH 3.7-5.1) and storage temperature (4°, 8°, and 12°C). At each storage temperature, LM was able to grow in the seafood salad. The growth was significantly slower in salads stored at lower temperatures, and only slightly affected by the acidity of mayonnaise. Growth rates of LM in salad under various conditions were produced. The growth rates were used to develop mathematical models that can be used by food processors, distributors and retailers to determine factors that control the growth of L. monocytogenes in seafood salad.
Technical Abstract: Seafood salad has been identified as a ready-to-eat food with a relatively high incidence of contamination by Listeria monocytogenes; however, little is known about the behavior of this pathogen in seafood salad as a function of product pH and storage temperature. To produce data towards the development of a predictive growth model, a 6-strain cocktail of L. monocytogenes was inoculated onto the surface of a shrimp-crabmeat product, mixed with mayonnaise that was previously adjusted with NaOH to pH 3.7, 4.0, 4.4, 4.7 or 5.1, and then stored at 4°, 8° or 12°C under both aerobic and vacuum conditions. At each storage temperature, L. monocytogenes was able to grow in the seafood salad under both aerobic and vacuum conditions. The slowest growth of L. monocytogenes was observed in seafood salad with a mayonnaise pH of 3.7 and a storage temperature of 4°C under vacuum conditions. In salad with the same mayonnaise pH, the growth rate (GR, log10 cfu/h) of L. monocytogenes increased as a function of storage temperature. At the same storage temperature, the lag phase duration (LPD, h) of L. monocytogenes decreased as mayonnaise pH increased. At the same mayonnaise pH, LPD of L. monocytogenes was greater under aerobic conditions than under vacuum conditions. Regression analyses indicated that mayonnaise pH is the main effect on the LPD of L. monocytogenes in seafood salad, and storage temperature was the main effect on the GR. Mathematical equations that describe LPD and GR of L. monocytogenes in seafood salad as a function of mayonnaise pH and storage temperature were produced.