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Dairy, Food and Environmental Sanitation
Abstracts - November, 2001
The Emergence of Food Microbiology: From Dairy Microbiology
to Food Microbiology
Survival and Growth of Escherichia coli O157:H7
in Solids-Fortified Skim Milk Stored at Low Temperatures
The Emergence of Food Microbiology:
From Dairy Microbiology to Food Microbiology
Elmer H. Marth
Department of Food Science and The Food Research Institute, University of
Wisconsin-Madison, Madison, WI 53706
SUMMARY
Courses in food microbiology were first taught in the 1930s, and the first
text on the subject appeared in 1944. Gradually, dairy industry departments
evolved into food science departments, which prompted increased interest in food
microbiology. The content of food microbiology courses changed over the decades
as new information became available. This information increased to the point
where additional courses were created in many universities to deal with such
topics as food fermentations, food sanitation, foodborne illnesses, and food
quality control. As course offerings grew, so did extension work, and many
universities added food microbiologists for this activity. Great progress has
been made in understanding and controlling food spoilage, canned food
processing, preservative use, pasteurization of eggs, application of the concept
of water activity in food processing, mycotoxins, foodborne illnesses,
psychrotrophic bacteria, food fermentations, and test method development. Food
microbiologists have participated in activities of various professional
societies, some serving as president of these societies, and many have been
recognized by the societies for their contributions to the discipline.
This is the second part of a two-part series.
Part 1 appeared in the October 2001 issue of DFES.
Survival and Growth of Escherichia
coli O157:H7 in Solids-Fortified Skim Milk Stored at Low Temperatures
Salam A. Ibrahim,* Maysoun M. Salameh, and
Theresa A. Lloyd
Food Safety Microbiology Laboratory, Department of Human Environment and Family
Sciences, North Carolina Agricultural and Technical State University,
Greensboro, NC 27411-1064
SUMMARY
The objective was to determine the effect of milk solids fortification on
the survival and growth of Escherichia coli (E. coli O157:H7,
strain 380-94) in skim milk stored at low temperatures. E. coli O157:H7
was inoculated into skim milk containing 8, 10, or 12% total solids to provide a
final inoculum level of 103 CFU/ml. The inoculated milk samples were mixed well
and held at 2°, 4° or 8°C for up to 3 weeks. Samples were collected at
different time intervals and diluted in peptone water; 100µl of each
appropriate dilution was plated in duplicate. Plates were incubated at 37°C for
24h. During storage period at 2°, and 4°, E. coli O157:H7 did not grow
and the population began to decrease after 6 days of incubation in the
unfortified samples; in the samples containing 12% solids, the number remained
unchanged during the incubation period. During storage at 8°C, a 2-3 log CFU
/ml increase in E. coli O157:H7 was observed in all milk samples, but
growth was higher (P <0.01) in fortified than in unfortified milk
samples. These results showed that fortification of skim milk with milk solids
would promote the survival and growth of E. coli O157:H7 or maintain
initial levels at low temperature storage. Results also indicated that elevated
milk solids provide protection against death during cold storage.
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