The influence of mayonnaise pH and storage temperature on the growth of Listeria monocytogenes in seafood salad

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 condition. 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 and temperature, LPD of L. monocytogenes was greater under aerobic than under vacuum conditions. Regression analyses indicated that mayonnaise pH is the main effector on the LPD of L. monocytogenes in seafood salad, and storage temperature was the main effector on the GR. Secondary models that describe LPD and GR of L. monocytogenes in seafood salad as a function of mayonnaise pH and storage temperature were produced.