2-19. A KEEPING QUALITY EXAMINATION (MOSELY TESTING)
a. Purpose of the Examination. Keeping quality examinations are not
currently contractual. The purpose is to check for levels of psychrophilic bacteria. This
examination can provide a valuable source of feedback information on plant sanitation
(post-pasteurization contamination) causing excessive contamination of the fresh dairy
product by psychrophilic bacteria.
b. Growth Rate of Psychrophilic Bacteria. The word "psychrophilic" meaning,
"cold loving" is somewhat of a misnomer in describing these bacteria. It is a relative
term covering bacteria that have the ability to grow at somewhat lower temperatures
than most such organisms. This should not be interpreted to mean that they prefer low
temperatures for growth. In general, the growth rate in milk at 32F (0C) is so slow that
more than one day may be required for a cell to divide once. At 40F (4C), several
divisions may take place in a day. At 45F (7C), the divisions are markedly increased
and are complicated by the slow growth of nonpsychrophilic bacteria whose initial
contamination may have been much greater.
c. Using Official Laboratories. The official medical laboratories always
conduct mosely Testing. When selecting samples for routine wholesomeness testing,
additional samples should be selected and submitted for Mosely Testing.
d. Shipment. The veterinary food inspection specialist selects three containers
of product, side by side, that have been maintained at 40F or less. The samples are
prepared for shipment to the laboratory. Sufficient refrigerant must be used to ensure
that the arrival temperature at the laboratory is 40F or less.
e. Testing Results. Upon arrival at the laboratory, one sample will be tested
immediately. The second sample will be tested after 5 days. The final sample will be
tested after 7 days. Any test result in excess of 1,000,000 standard plate count (SPC)
is an indication of post-pasteurization contamination. Laboratory test results with SPC
counts in excess of 1 million/mL 7 days after pasteurization for an unopened container
of pasteurized milk (maintained at 45F) indicate a post-pasteurization contamination
with psychrophilic bacteria. A record of this in several products or repetitive high counts
in several samples of the same product over time indicates that the plant may have a
sanitation or equipment problem. In addition, it indicates the potential for introduction
and proliferation of Listeria monocytogenes or Yersinia enterocolitia. Also, the presence
of a high count of psychrophilic bacteria will shorten the shelf-life of the product and
does not represent good manufacturing practices achievable with today's technology.
f. Reporting Problems. Any indication of keeping quality problems must be
reported to the origin inspector. This type of result would dictate that a quality
assurance visit (QAV) to the production plant be scheduled.