Fate of Listeria monocytogenes, Salmonella typhimurium DT104, and Escherichia coli O157 : H7 in Labneh as a pre- and postfermentation contaminant

Commercially pasteurized milk (similar to 2% milkfat) was heated at 85 to 8 7 degrees C/30 min, inoculated to contain 2,000 to 6,000 CFU/ml of Listeria monocytogenes, Salmonella Typhimurium DT104, or Escherichia coli O157:H7, cultured at 43 degrees C for 4 h with a 2.0% (wt/wt) commercial yogurt star ter culture, stored 12 to 14 h at 6 degrees C, and centrifuged to obtain a Labneh-like product. Alternatively, traditional salted and unsalted Labneh was prepared using a 3.0% (wt/wt) starter culture inoculum, similarly inocu lated after manufacture with the aforementioned pathogens, and stored at 6 degrees C and 20 degrees C. Throughout fermentation, Listeria populations r emained unchanged, whereas numbers of Salmonella increased 0.33 to 0.47 log s during the first 2 h of fermentation and decreased thereafter. E. coli po pulations increased 0.46 to 1.19 logs during fermentation and remained that these levels during overnight cold storage. When unsalted and salted Labne h were inoculated after manufacture, Salmonella populations decreased >2 lo gs in all samples after 2 days, regardless of storage temperature, with the pathogen no longer detected in 4-day-old samples. Numbers of L. monocytoge nes decreased from 2.48 to 3.70 to <1.00 to 1.95 logs after 2 days with the pathogen persisting up to 15 days in one lot of salted/unsalted Labneh sto red at 6 degrees C. E. coli O157:H7 populations decreased from 3.39 to 3.7 to <1.00 to 2.08 logs during the first 2 days, with the pathogen no longer detected in any 4-day-old samples. Inactivation rates for all three pathoge ns in Labneh were unrelated to storage temperature or salt content. Unlike L. monocytogenes that persisted up to 15 days in Labneh, rapid inactivation of Salmonella Typhimurium DT104 and E. coli 0157:H7 suggests that these em erging foodborne pathogens are of less public health concern in traditional Labneh.