61C-40 |
Survival and growth of Escherichia coli O157:H7 in pasteurized and unpasteurized Cheddar cheese whey |
P. MAREK, M. K. Mohan Nair, T. Hoagland, and K. Venkitanarayanan. Animal Science, University of Connecticut, 3636 Horse barn hill road, G.White Building, Storrs, CT 06269 Escherichia coli O157:H7 is a major foodborne pathogen in the United States. Although contamination of milk and cheese with E. coli O157:H7 has been reported, risks of E. coli O157:H7 associated with whey has not been investigated. The objective of this study was to determine the survival and growth characteristics of E. coli O157:H7 in whey. A five-strain mixture of E. coli O157:H7 was inoculated into 100 ml of fresh pasteurized or unpasteurized cheddar cheese whey (pH 5.5) at 105 or 102 CFU/ml, and stored at 4, 10, or 15ºC. At each inoculation level, triplicate samples of pasteurized and unpasteurized whey were included at each temperature. The population of E. coli O157:H7 (Sorbitol MacConkey agar) and lactic acid bacteria (All Purpose Tween agar) were determined on days 0, 1, 4, 7, 14, 21, and 28. At all storage temperatures, survival of E. coli O157:H7 was significantly higher (P < 0.01) in the pasteurized whey compared to that in unpasteurized samples. At 10 and 15ºC, E. coli O157:H7 in pasteurized whey significantly increased during the first week of storage, followed by a decrease thereafter. However at the same temperatures, E. coli O157:H7 exhibited a steady decline in the unpasteurized samples from day 0. At 4ºC, E. coli O157:H7 did not grow in pasteurized and unpasteurized whey, however the pathogen persisted longer in pasteurized samples. At all the three storage temperatures, E. coli O157:H7 survived up to day 21 in the pasteurized whey, whereas the pathogen was completely killed after day 14 in the unpasteurized samples. Greater than 3.0 log CFU/ml of lactic acid bacteria survived in unpasteurized whey at all temperatures, with the highest counts recovered at 4ºC. Results indicate the potential risk of persistence of E. coli O157:H7 in whey in the event of contamination with this pathogen.
Session 61C, Food Microbiology: General I
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