61C-34 |
Behavior of Listeria monocytogenes in pasteurized and unpasteurized goat milk at different storage temperatures |
L. LEUCHNER1, T. Annamalai1, T. Hoagland1, Y. Zhao2, and K. Venkitanarayanan1. (1) Animal Science, University of Connecticut, 3636, horsebarn hill road extension, G.White building, Storrs, CT 06269, (2) Food science, Oregon state university, 100, wiegand hall, Department of food science and technology, Corvallis, OR 97331 Listeria monocytogenes is a foodborne pathogen commonly associated with farm animals, including goats. L. monocytogenes has also been found in milk of healthy and mastitis affected goats. However, the risks of L. monocytogenes associated with goat milk have not been investigated. The objective of this study was to determine the survival and growth characteristics of L. monocytogenes in goat milk. A three-strain mixture of L. monocytogenes was inoculated into 100 ml of fresh pasteurized or unpasteurized goat milk (pH 6.7, 5.2% fat) at 106 or 103 CFU/ml. The inoculated milk samples were stored at 4º, 10º, or 15ºC. At each inoculation level, triplicate samples of pasteurized and unpasteurized goat milk were included at each temperature. The population of L. monocytogenes (Oxford agar) and total bacterial load (Tryptic Soy agar) were determined on days 0, 1, 3, 7, 9, and thereafter every week until day 58. At all storage temperatures, the survival of L. monocytogenes was significantly higher (P<0.05) in pasteurized milk, compared to that in unpasteurized samples. In unpasteurized milk inoculated at both levels, L. monocytogenes survived throughout the study at all temperatures except at 15ºC. At 15ºC, L. monocytogenes could not be detected after 44 days of storage. In pasteurized milk inoculated with 103 CFU/ml, L. monocytogenes population on day 58 increased by approximately 3 log CFU/ml at 4ºC and by 4 log CFU/ml at 10ºC or 15ºC. However, at the three storage temperatures, no significant (P>0.05) increase in L. monocytogenes counts was observed in the pasteurized samples inoculated with 106 CFU/ml. At all storage temperatures, the total bacterial load in the pasteurized and unpasteurized milk increased by approximately 5 log CFU/ml on day 58. The results indicated that L. monocytogenes can survive in goat milk for long periods of time in the event of contamination with this pathogen.
Session 61C, Food Microbiology: General I
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