Investigation on the viability span of Listeria monocytogenes during the ripening of brined savak cheese

Abstract

The purpose of this study was to determine the viability span of listeria monocytogenes during the ripening of brined Savak white cheese which is produced by and has a significant role in the nutrition of people living in Elazig. Tunceli, Bingol and Erzincan. Ewes milk was inoculated with various strains (4b, 1/2c and 1/2a) of listeria monocytogenes at the rate of 1.00x10(3) 1.35x10(6) cells/ml and then Savak cheese was produced from the milk. The cheese samples were analysed after 0, 15, 30, 60, 90 and 120 days of ripening for the numbers of listeria monocytogenes with the direct plating method and enrichment methods (at 30 degrees C for 48 hours or 7 days). The numbers of listeria monocytogenes were 3.70x10(5) - 6.88x10(5) cfu/g in the curd, which fell to 0.50x10-7.08x10 cfu/g in the cheese after 120 days of ripening and the trends were almost identical. The numbers of listeria monocytogenes determined with the enrichment methods, followed different paths during the ripening. The pH of the cheese until day 60, in all series of the samples. Later in the experiment (days 90 and 120) the values increased. It was conluded that it might be possible to isolate listeria monocytogenes from Savak cheese made from raw ewes milk containing a minimum of 1.00x103 cells/ml; using direct isolation rate in enrichment at 30 degrees C for 48 hours is higher than in enrichment at 30 degrees C for 7 days. In addition, it was evident that listeria monocytogenes survive until the end of the ripening process and pose a danger to public health.