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Pate, Brad (ed.) / Wisconsin engineer
Volume 110, Number 3 (April 2006)

Jayne, Kevin
Plasma processing: researchers help take microbes off the menu,   pp. 12-13 PDF (871.4 KB)

Page 12

By Kevin Jayne
T         at types of thoughts cross your
ind when presented with a
 scrumptious meal on an empty
In all likelihood, microscopic pathogens are
not one of them. However, food-borne dis-
eases caused millions of illnesses and thou-
sands of deaths in the past year alone. These
contaminants are a problem that will continue
to fester until action is taken to stop them.
New technology developed at UW-Madison
may be a step in the right direction.
Frank Denes, UW-Madison professor of bio-
logical systems engineering, has created a
method of using cold plasma to defeat food-
borne pathogens before they reach the con-
sumer. For now, the innovative idea remains in
the developmental stages, though it appears
very promising and could someday have
industrial applications.
Plasma is generated by passing a gas through
a high voltage electric field. The electrons this
field accelerates bombard the gas molecules,
converting them into a mixture of ions and
free radicals. Unlike hot plasma, which can
reach temperatures of thousands or millions of
degrees Fahrenheit in the vacuum of outer
space, cold plasmas are created with the atom-
ic or molecular species at close to room tem-
perature and at low or standard atmospheric
"A cold plasma exists in a gas environment
that is ionized and at a low temperature. The
ionization degree and temperature of the
atomic species is low, but the energy of the
electrons is high," Denes says.
This combination of high energy and low tem-
perature can give cold plasmas useful disin-
fectant properties. But researchers must first
choose which gases to use in achieving the
desired end-use properties.
"We are using air, oxygen and mixtures of air
with moisture for our disinfection purposes.
For other applications we can use different
types of gas--they will produce different sur-
face characteristics," Denes says.
New technology developed
at UW-Madison could help
reduce food-borne
Denes collaborated with Amy Wong, a UW-
Madison professor of food microbiology and
toxicology, to develop this technology. His
innovation has helped him secure two patents
through the Wisconsin Alumni Research
Foundation (WARF): one for a device to treat
solids and another for a device to treat liquids.
Cold plasma technology has been in existence
for decades. However, Denes' machines are
specially designed to work at atmospheric
pressure for decontamination and disinfection
Capable of generating and releasing cold plas-
ma species at a steady rate, Denes' first piece of
equipment is the Array Electrode Reactor. This
device is composed of over 200 closely spaced
cylindrical wire electrode chambers. Arranged
in a grid, these chambers control the distribu-
tion of plasma over the surface to be treated.
"Individual plasma reactors are working [in]
parallel and generate reactive plasma species
which are blown over surfaces that are con-
taminated. Using this technique, we found
that disinfection is fairly efficient," Denes says.
With only a few minutes of cold plasma treat-
ment, this apparatus decreases the number of
bacteria by a factor of thousands. Researchers
suspect plasma kills pathogens by altering the
surface of their cell membranes, interfering
with necessary metabolic processes.
"The plasma species are already energetic.
Their energy levels are comparable to other
common bonding energies found in organic
compounds. By applying the plasma to the
surface, the action interrupts these chemical
bonds, causing them to decompose and killing
the bacteria," Denes says.
Denes' second invention achieves a very simi-
lar goal, but this device treats liquids.
Approximately one liter of the substance to be
treated is enclosed in a container. The device
12   APRIL 2006

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