fate of listeria monocytogenes during ripening of iranian traditional koozeh cheese made from raw ewe's milk

Background: one of the most well-known iranian traditional cheeses is koozeh. the aim of present work was to evaluate the survival of l. monocytogenes during ripening of iranian traditional koozeh cheese made from raw ewe's milk. methods: a 2-factor experimental design was applied to study the effect of ripening conditions, including different temperatures (4, 9, and 14 °c) and different concentrations of nacl (0, 8, 12, and 15%) on the survival of l. monocytogenes in the koozeh cheese. microbial analysis was carried out over a period of 150 days with sampling in every 10 days. spss software (v. 16.0) was used for statistical analysis. results: three nacl concentrations (8, 12, and 15%) significantly affect the inactivation l. monocytogenes (p<0.05). after inoculation, l. monocytogenes populations were reduced most rapidly during the first ten days of storage (~0.5-1.5 log colony forming unit/g) at three mentioned temperatures; after that, the bacteria were continually decreased, being below the detection limit (1 log cfu/g) at the end of ripening. numbers of l. monocytogenes were reduced more effectively at 14 °c storage temperature than 9 and 4 °c (p<0.05). conclusion: l. monocytogenes was declined drastically during ripening days and elimi-nated at the end of ripening of koozeh cheese. l. monocytogenes counts were decreased during ripening of koozeh cheese under adverse conditions such as high salt concentrations and high temperatures. however, since iranian koozeh cheese is made from raw and unpasteurized milk, there are still some concerns about health risk of l. monocytogenes in this product. also, the effects of temperature and salting parameters on the sensorial properties of koozeh cheese should be investigated in future.