When a strain of E. coli bacteria in ground
beef sickened more than 400 people, the micro-organism became a subject
of heightened interest to researchers.
The latest outbreak of the bacteria in apple juice
has added fuel to the efforts to determine its sources of origin, find a
way to test for its presence and ensure the safety of food products.
One research effort has just been launched under
the auspices of the United States Apple Association (see accompanying column
by USAA President Ellen Terpstra).
At Cornell University, a project is underway to
look at alternative processing methods for cider which will result in a
product that is safe and tastes good. Mark McLellan, director of the Cornell
Institute of Food Science and professor emeritus of food science Don Splittstoesser
are spearheading the project. The project is funded by a two-year USDA grant,
which the two researchers believe is the only federal grant devoted to this
particular problem.
Pasteurization is still the best way to avoid
the threat of E. coli, but its downside is its effect on taste. However,
some studies suggest that cider flavor can be enhanced with minimal heat
treatment. Previous research by Splittstoesser on Empire apple cider shows
that the E. coli 0157 strain is heat sensitive, especially when the preservative
benzoic acid is present.
After determining the minimal process needed to
eliminate E. coli, this process will be applied to ciders prepared in the
New York State Agricultural Experiment Stationís Geneva pilot plant
while testing various methods of pasteurization.
ìIdeally, these processes will duplicate
the range of potential processes used by cider mills whether they are very
small and use a simple heating kettle to large scale operations having tube
and shell heat exchanges,î said McLellan.
Cornell researchers have also developed a way
to detect the presence of E. coli in foods in hours rather than days. Carl
Batt, professor of food science, and graduate student John Czajka have a
method which cuts the time from 48 hours to about seven hours. Their research
was sponsored by Idetek of Sunnyvale, Calif., which has patent rights. The
technology is not yet available for the marketplace.
An assay is carried out in thin glass tubes. Bacterial
cells are captured from the food using microscopic magnetic beads and then
placed into a growth medium that allows the bacteria to replicate, which
makes their detection easier. After a few hours of incubation, researchers
than add an antibody specific to E. coli O157 that is marked with a fluorescent
dye. The antibody binds to the bacteria and fluoresces when illuminated
with a laser.
The bacteria is known to exist in cattle, but
what about wild animals, such as deer? Results from work on this issue at
the University of Georgiaís Southeastern Cooperative Wildlife Disease
Study will soon be published.
John Fischer, assistant research scientist, said
a sample of deer taken in 1992 for the Centers for Disease Control showed
no presence of E. coli in deer. However, when fawns were infected with the
bacteria, the pattern of their infection was equivalent to that of calves.
The bottom line, he said, is that deer feces cannot be positively identified
or ruled out as a source of E. coli until more research is conducted.