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Isolation and Identification of Microorganisms Responsible for Ropy Milk


1. Isolate and identify microorganism(s) responsible for ropy milk. </P>
2. Determine correlation (if any) between type/levels of responsible microbe(s) recovered in raw milk with those recovered from ropy pasteurized milk </P>
3. Enumerate the causative microorganism to determine typical populations. </P>
4. Determine seasonality during a one-year period. </P>
5. Improve existing test to more accurately and consistently reproduce ropy phenomenon, if needed. </P>
6. Type selected isolates by pulsed field gel electrophoresis (PFGE) at least quarterly.

More information

Ropy milk is a quality defect that is occasionally reported during the extended shelf-life of pasteurized milk. More frequently, ropiness was observed in raw milk samples that were screened by incubating samples at 16-22?C (60-72?F) for 24 to 36 hours. The ropy milk phenomenon is rarely reported to manufacturers by consumers during typical refrigerated storage of pasteurized milk. However, anecdotal reports of increased incidence during quality checks suggest the causative microorganisms are either not eliminated during HTST pasteurization or cannot be controlled in packaged, pasteurized milk containers using typical cleaning and sanitation procedures. This study isolated and identified S. constellatus and S. intermedius as the primary organisms responsible for ropy spoilage of raw and pasteurized milk and developed a control method.

Glass, Kathleen; Wong, Amy
University of Wisconsin - Madison
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