Science News Online - Food for Thought - 2/14/98
February  14, 1998
A polished approach to food safety
Kitchen hygiene should be an important part of the recipe for
any meal. It involves not only frequent hand washing and
cleansing of food preparation surfaces with sanitizing rinses
(see To disinfect your salad), but also making sure that
foods spend as little time as possible at room temperature.
In most cases, the goal of these practices is to limit the
growth and transfer of germs that hitched a ride into the
kitchen along with the food. But where do these germs come from?
Most of those in chicken and eggs appear to trace to infections
passed around the chicken coop (SN: 5/26/96, p. 326). In other
cases, they can come from a single "bad apple," so to speak --
one contaminated carcass or vegetable that sheds a few of its
germs on equipment in the food-processing plant, which then goes
on to taint subsequent foods running through that equipment.
In hopes of stemming this cross-contamination of materials in
food-processing plants, researchers have been studying what
types of surfaces offer the least receptive homes for germs.
Judy W. Arnold believes she has stumbled onto a particularly
inhospitable one in electropolished steel.
Shiny is better
A microbiologist with the Department of Agriculture's Poultry
Processing and Meat Quality Research Unit in Athens, Ga., Arnold
has been testing the attractiveness of various materials used in
poultry-processing equipment to the Salmonella, Campylobacter,
and other food-poisoning bacteria that commonly infect chickens.
In general, she notes, the more porous the surface, the better
bacteria like it. That's why conveyor belts made from chains of
polyethylene links are particularly vulnerable. Her findings
suggest that the more old-fashioned, solid rubber belts might be
While ordinary stainless steel, a standby of food processors, is
not porous, it does provide a safe haven for microbes. Its
surface appears smooth to the naked eye, but nooks and crannies
show up under scanning electron microscopes. These microcrevices
can give at least some bacterial squatters shelter from the
chemical and mechanical cleansers designed to evict them.
Electropolished stainless steel undergoes an acid bath, followed
by a finishing step that sends an electric current through the
metal. What emerges is a far shinier steel with an almost
More important, fewer bacteria took up housekeeping on the
Arnold is at work investigating why. She suspects that the
finishing step may impart a negative charge to the surface that
repels bacteria, which tend to carry a negative charge
themselves. However, she points out, "charge is probably only
one of several factors that play an important role." After all,
she notes, the surface charge on the metal probably doesn't last
long in an environment subjected to all type of charged
materials, including water, manure, blood, and tissue. "So the
smoothness of this steel probably makes a great deal of
Food processors clean their equipment frequently with
high-pressure sprays and liberal dowsings of disinfectants, but
they can't do this between each animal processed. The
evisceration machines in some poultry plants, for instance,
process 90 to 140 birds a minute.
What's more, bacteria are a very sociable lot. A pioneering bug
will quickly set up colonies of hundreds or thousands of
progeny. Each of the initial homesteaders lays down filamentous
fibrils that not only help anchor it to the metal but also tend
to link it to adjacent bacteria (see photo 1). Successive waves
of unrelated bacteria then join them to create a multicultural
community of microbes. Often, some of the later emigrants exude
a gluey film that eventually covers the entire community.
Studies have shown that such biofilms are particularly resistant
to removal (SN: 7/20/85, p. 42).
Manufacturers are looking for ways to cut down on the buildup of
bacteria and to evict them before the biofilm producers arrive.
If food processors can limit the initial adhesion of these
microbes so that cleansers can do a more thorough job -- or
better yet, so that smaller quantities of disinfectants are
needed -- they stand to improve not only the safety of their
products, but also their bottom line.
Though more expensive than ordinary stainless steel, that's what
electropolished steel seems to offer, Arnold says.
In follow-up studies, she hopes to identify ways of optimizing
this metal's resistance to bacteria.
Lee, J. 1998. Bacterial biofilms less likely on electropolished
steel. Agricultural Research 46(February):10. Also available on
the WEB at:
Raloff, J. 1998. Staging germ warfare in foods  . Science
News 153(Feb. 7):89.
_____. 1997. Cutting through the cutting board brouhaha, 
Science News Online(July 12).
_____. 1996. To disinfect your salad  . Science News Online
_____. 1996. Sponges and sinks and rags, oh my!  Science
News 150(Sept. 14):172.
_____. 1996. Tracking and tackling foodborne germs. Science News
_____. 1985. Biocorrosion: Widespread vulnerability. Science
News 128(July 20):41.
_____. 1985. The bugs of rust. Science News 128(July 20):42.
1996. Food safety: Information on foodborne illnesses. Report
RCED-96-96 (May). U.S. General Accounting Office, Washington, DC
Judy W. Arnold
Poultry Processing and Meat Quality Research Unit
Russell Agricultural Research Center
950 College Station Rd.
Athens, GA 30604
This week's Food for Thought has been prepared by Janet Raloff,
senior editor of Science News.
copyright 1998 Science Service 
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