Determination of Nisin Concentration to Control Listeria monocytogenes in Cooked Ham

Listeria monocytogenes contamination may occur after thermal processing of cooked ham. This study aimed to determine the effective nisin concentration to inhibit the growth of L. monocytogenes. Two batches of ham were prepared by adding 12.5 mg nisin/kg ham at brine injection (assay 1) or tumbling stage (assay 2). Another piece of cooked ham was prepared by adding 32 mg nisin/kg ham at brine injection (assay 3). Afterward, samples of cooked ham were contaminated with L. monocytogenes cocktail (4 log CFU/mL). The results of assays 1 and 2 revealed that this nisin concentration was ineffective in inhibiting L. monocytogenes in ham. The minimum bactericidal concentration test results indicated that each L. monocytogenes strain had a different sensitivity profile and the cocktail had greater resistance. High concentrations of nisin (32 mg/mL) were efficient in controlling the most resistant strains. Statistical analyses were performed using ANOVA and Tukey's test. This higher nisin concentration was effective in controlling the L. monocytogenes cocktail in cooked ham over 10 days. The findings highlight the potential of high nisin concentrations to effectively reduce L. monocytogenes contamination in cooked ham.