THE EFFECT OF POTASSIUM SORBATE AND pH ON THE GROWTH OF LISTERIA MONOCYTOGENES IN HAM SALAD

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.