Inhibitory effect of nisin-producing Lactococcus lactis on survival of Listeria monocytogenes strains in ultra-filtered white cheese

Listeria monocytogenes (Lm) is an important foodborne pathogen that is of great importance in milk and its products. Despite the measures taken to eliminate and control Lm contamination in pasteurized milk products, but due to its high spread in the environment, there is a possibility of secondary contamination in products such as Ultra-filtered (UF) white cheese. This study aimed to investigate the inhibitory effect of nisin-producing Lactococcus lactis on Lm in Ultra-filtered white cheese. Ultra-filtrated and pasteurized cow's milk was inoculated with 3 Log CFU/g of standard or native strains of Lm and control and treatment (containing nisin-producing L. lactis) cheese samples were manufactured. Changes in the population of Lm and nisin concentration were estimated throughout the storage period. According to the results, in all groups, the population of Lm began to decrease from day five onwards. Nonetheless, the decreasing trend in the treatment samples and in parallel with the production of nisin was significant (p < 0.01). The native strain of Lm was significantly (p < 0.01) more resistant than the standard one. Since the nisin-producing L. lactis, despite inhibiting Lm, did not negatively affect the growth of starter bacteria and the resulting pH decline of the cheese samples. Consequently, nisin-producing L. lactis can be used to control some bacterial contamination of the UF white cheese. It is also necessary to study the behavior of native strains isolated from food samples along with laboratory strains in inoculation studies.