Inhibition of Listeria monocytogenes by Nisin During Manufacture of White Pickled Cheese


Abstract: This study based on the effect of nisin on Listeria monocytogenes in white pickled cheese made from pasterurized milk during the ripening and storage period for 60 days. For this purpose, four groups of cheese were produced. All groups were inoculated with the L. monocytogenes 1/2a test strain at the levels of 10^4-10^5 cfu/ml. Group I was remained as a control group (contained no starter culture and nisin). Group II was added a mixture culture of the commercial starter culture Lactococcus lactis and Lactococcus cremoris in a proportion of 2 % , while in group III was added the same starter culture with 30 \mug/ml nisin, and group IV contained only 30 \mug/ml of nisin. In this way, 3 productions were realized. FDA suggested method was used for the isolation of L. monocytogenes and the development of L. monocytogenes during this period was determined using Most Probable Number (MPN) technic. Regarding the group I cheeses, at the end of the first 24 hours, the number of L. monocytogenes increased 3-4 log; in the group II cheeses, with an increase of approx. 1 log, in turns it reached the level of 10^7-10^8 MPN/g and 10^5 MPN/g without any important change during the ripening and storage period and it remained at this level until the end of 60th day. In the groups III and IV cheeses, after the first 24 hours there was a decrease of more than 2 and 3 log in the number of L. monocytogenes and in the group III cheeses, the number of L. monocytogenes gradually decreased and it was either totally eliminated or it remained at a level of 0.23 MPN/g, while in the group IV cheeses, the agent gradually decreased and it was totally eliminated at the end of the 60th day. As a result, it has been ascertained that nisin has a strong bactericid effect on the L. monocytogenes. So this important foodborne pathogens was eliminated from white pickled cheese during the ripening and storage period for 60 days with adding of 30g/ml nisin.

Keywords: White pickled cheese, L. monocytogenes, nisin, starter culture, inhibition, MPN

Full Text: PDF