Inhibition of Listeria monocytogenes during cheese manufacture by adding nisin to milk and/or using a nisin-producing starter
Food Ingredients Europe Conference Proceedings, Porte de Versailles, Paris 4, 5, 6 October 1993: 58-64
A model system using tryptic soy broth (Difco) + 0.6% yeast extract as culture medium and non-pathogenic Listeria innocua as test organism, was developed for studying the anti-listerial activity of low nisin concn, and the combined effect on it of pH and temp. Irrespective of nisin concn up to 200 IU/ml, pH of medium or temp. of incubation, addition of nisin was followed by a rapid drop in listeria count. Results are reported of pilot-scale studies on the manufacture of Camembert cheese from pasteurized milk that had been artificially contaminated with L. monocytogenes VT, using nisin-producing (Nis+) and nisin-negative strs of Lactococcus lactis var. lactis as starter. The listeria count decreased during the 1st 24 h in cheese made with Nis+ starter, but regrowth of listeria occurred in all cheeses as the pH increased, and was observed sooner in the crust than in the core of the cheese. Addition of small amounts of nisin to the cheese milk, either with or without heat treatment, combined with the use of Nis+starter, considerably improved the anti-listerial effect.