The Effect of Potassium Sorbate and pH on the Growth of Listeria Monocytogenes in Ham Salad

Abstract

This study examined the growth of Listeria monocytogenes in ham salads of various pHs and sorbate concentrations. Ham was inoculated with L. monocytogenes and mixed with potassium sorbate (0–0.2%) and mayonnaise to achieve salad pHs of 5.4–5.8. The population increases of L. monocytogenes in salads stored at 4C for 4 weeks were correlated to salad pH and sorbate concentration. In salads with pHs of 5.4–5.8 containing 0.0, 0.1, 0.15 and 0.2% sorbate, the populations of L. monocytogenes increased 2.7–6.4, 2.4–5.2, 1.0–3.7 and 0.2–2.0 log cfu/g, respectively. A polynomial model was developed to describe the population increases as a function of salad pH and sorbate concentration. It indicated that the increases of L. monocytogenes were significantly lower (P < 0.05) in salads containing higher sorbate concentrations. Results from this study will help identify the salad pH and sorbate levels that reduce the hazard of L. monocytogenes in mayonnaise-based salads. Practical Applications Delicatessen salads are susceptible to Listeria monocytogenes contamination. The products receive no terminal heat treatment during manufacturing and are ready-to-eat without further cooking. The ability of L. monocytogenes to grow at refrigerated temperature makes it a significant public health hazard in salads. Potassium sorbate is a generally recognized as safe preservative used in various food products. This study identified the levels of sorbate in combination of salad pH that were capable of controlling the growth of L. monocytogenes in a model ham salad. The information can be used by salad producers to formulate their products with the addition of sorbate to reduce L. monocytogenes hazard in mayonnaise-based salads.