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<ol> <li>Analysis of subpasteurization procedures on the indigenous microflora of raw milk
<li>Analysis of the efficacy of subpasteurization on Salmonella spp., L. monocytogenes and E. coli O157:H7
<li>Determine the efficacy of subpasteurization of milk in combination with optimal aging period for inactivating Salmonella spp., L. monocytogenes and E. coli O157:H7 in raw milk cheese
<li>Determine the role of subpasteurization temperatures on inducing heat tolerance in Salmonella spp., L. monocytogenes and E. coli O157:H7, and
<li>Determine the potential for acid adaptation in Salmonella spp., L. monocytogenes and E. coli O157:H7 following long periods of aging and survival in cheese.</ol>
Objective 1 and 2: Raw milk samples will be obtained from Cheddar cheese manufacturer(s)who are presently utilizing a subpasteurization heat treatment of their cheese milk. Samples will be evaluated for total plate count and also for colonial morphology. Milk samples will be processed following the temperature parameters in use with the cheesemakers. Preliminary determinations of sub pasteurization temperature will range from 48-55(C for various time periods, using vat pasteurization. The population of indigenous bacteria,of the samples will be re-evaluated to determine the efficacy of the treatment in reducing the bacteria. Further, the efficacy of subpasteurizatoin heat treatment procedures on Listeria monocytogenes, Salmonella species and E. coli O157:H7 will be determined. Sterile milk (UHT/aseptically packaged) milk will be inoculated with the above noted human pathogenic microorganisms and processed via the subpasteurization heat treatment time-temperature parameters. Samples of the milk will be evaluated pre and post processing to determine the reduction of the number of organisms present in the samples.
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Objective 3: The experiment will be conducted separately with two different types of cheese, namely aged raw milk Cottage cheese and aged Feta cheese made with raw goat milk. Cow milk and goat milk will be inoculated separately with a three-strain mixture of each pathogen at low level (1000 CFU/ml) or high level (1000000 CFU/ml), and subjected to different subpasteurization treatments. Immediately following each treatment, the total plate count, and the populations of the pathogens will be determined. The inoculated milk subjected to the treatments will be subsequently used for making the respective cheese as per the method followed by the respective cheese maker participating in the project. Before aging (day 0), and at specified times during aging (days 15, 30,45, 60, and until detected) the population of inoculated pathogens in the cheese will be determined.</p>
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Objective 4: To determine the role of subpasteurization temperatures on inducing acid or heat tolerance in Salmonella spp., L.monocytogenes, and E. coli O157:H7, milk samples separately inoculated with a strain of each pathogen at 1000000 CFU/ml, and subjected to different subpasteurization treatments. Immediately after the treatment, the population of the pathogens will be enumerated on tryptic soy agar. The milk samples will be tempered to room temperature (24oC), and will be used for acid or heat tolerance assay.</p>
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Objective 5: The experiment will be conducted separately with two different types of cheese, namely aged raw milk Cottage cheese and aged Feta cheese made with raw goat milk. Each milk will be inoculated separately with a strain of each pathogen at 1000000 CFU/ml,subjected to different subpasteurization treatments, and used for making the respective cheese as per the method followed by the respective cheese maker participating in the project. Before aging (day 0), and at specified times during aging (days 15, 30, 45, and 60), the population of inoculated pathogens in the cheese and their acid tolerance in synthetic gastric juice will be determined.</p>