Bacteria
can grow on stainless steel surfaces, contaminating food. Current coatings
available on the market are pricey and potentially harmful, so scientists have
now developed an affordable specialized polymer coating for such surfaces that
they can recharge with bleach treatments.
The researchers are
presenting their results at the 255th National Meeting & Exposition of the American
Chemical Society (ACS). Current efforts to avoid such bacterial growth
incorporate silver or copper ions, which can be pricey. "In addition,
silver and copper are usually alloyed in the metal, and they have been tucked
away so they are not very effective," Demir notes. "There is also a
health concern with using silver." Silver could leach from the stainless
steel and into foods that are later consumed, she says.
Other
groups have linked N-halamine polymers to
stainless steel surfaces with the aid of a binder, but Worley's team has now
shown, for the first time, that N-halamine can be attached to stainless steel
directly. To do this, the researchers first roughed up the surface with
hydrogen peroxide and sulfuric acid. This creates negatively charged oxygen
groups on the surface to which the N-halamine polymer can attach through a
chemical reaction. When the researchers put bacteria on the coated surface, the
microbes did not grow. Demir tested many types of bacteria, including E. coli
and Staphylococcus aureus, which are common culprits implicated in many
foodborne bacteria outbreaks at food processing facilities. All of the bacteria
tested were killed within 15 minutes of coming into contact with the treated
surface.
Bleach contains
chlorine, a halogen, which by itself is extremely unstable; however, when
attached to the N-halamine polymer, it becomes stable. When bacteria come into
contact with the treated surface, the chlorine is released, killing the
bacteria."
Future plans include
manipulating the surface of stainless steel in a more user-friendly way.
"The greatest challenge is roughing the surface of the stainless steel.
Although this is easily done in the laboratory, it would not be easily done in
a manufacturing plant," Worley states. "We need a better way of
attaching N-halamines to the surface, and we have some ideas as to how we can
do that." The researchers also need to perform toxicity testing on samples
to investigate the safety of the coated surfaces and examine any biofilms that
may develop. "An antimicrobial surface in a food processing plant is badly
needed, and it could revolutionize the industry," Worley says.
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