January 30, 2003
Ozone may provide environmentally safe protection for grains
WEST LAFAYETTE, Ind. – Taking a clue from air purification systems used
in surgical suites, Purdue University researchers have discovered that
ozone can eliminate insects in grain storage facilities without harming
food quality or the environment.
Ironically, the gas is being touted as a fumigant alternative in
response to an international treaty banning the use of ozone-layer
harming chemicals currently used to rid food storage facilities of
insects. When ozone is used for killing grain insects, it lasts for a
very short period of time without damaging the environment or the grain,
the Purdue scientists report in the January issue Journal of Stored
"Ozone has a very short half-life and we're using relatively low
dosages, but enough to kill an insect," said
Linda Mason, Purdue entomology
associate professor and co-author of the study. "The chemicals currently
used can kill everything in and around the grain bin, including people.
With ozone, we're not generating ozone at deadly concentrations, and we
have better control over it when it's present."
Purdue's Post Harvest Grain Quality Research team began its studies in
response to the 1987 Montreal Protocol, an international agreement to
prohibit substances deemed dangerous to the Earth's ozone layer. One
such substance is methyl bromide, commonly used against crop pests in
the soil and in grain storage facilities. Beginning in 2005, it no
longer will be available.
replacement for chemical fumigants is imperative because insects not
only eat the grain, they defecate on it causing development of fungi,
primarily Fusarium and Aspergillus. These fungi can
release potentially deadly mycotoxins that can cause illness in most
livestock and have been linked to some forms of human cancer. In humans,
approximately 76 million cases of food-borne disease occur annually in
the United States, according to the Centers for Disease Control and
Experts estimate that 5 percent to 10 percent of the world's food
production is lost each year because of insects, and in some countries
that figure is believed to be as high as 50 percent.
the latest study, Purdue researchers used ozone to treat rice, popcorn,
soft red winter wheat, hard red winter wheat, soybeans and corn. They
used five-gallon plastic pails and 50-gallon steel drums, storage bins
filled with grain, and buried mesh bags all filled with grain and a
known number of grain-eating bugs to test ozone's killing efficacy. The
team's previous studies on ozone flow and effectiveness in eliminating
insects were done either in similar storage containers or in 500-bushel
bins built for pilot studies at the Purdue Agronomy Farm.
The ozone treatment of grain included two applications of ozone. In the
first, the ozone moves through the grain slowly because the gas reacts,
or bonds, with matter on the grain surface. This first treatment allows
ozone to react with most of the grain surface and degrades the ozone,
Mason said. With the second ozone application, the gas moves through the
grain more quickly because it isn't slowed by reactions with the grain.
This allows the ozone to kill the insects by reacting with them rather
than the grain.
Testing different grains allowed the scientists to answer two important
questions. One was whether ozone flowed differently through grains that
were less porous or of a different kernel size than corn, such as wheat.
The second was how exposure to ozone affects the quality of food
products made from the treated grain.
Dirk Maier, a Purdue agricultural
and biological engineering professor, studied how to make the ozone flow
efficiently and effectively through grain storage bins. Charles Woloshuk,
a botany and plant pathology professor, studied ozone effects on molds
and mycotoxins. Fidel Mendez, a botany master's degree student, studied
the final products produced from the treated grain to determine if they
were the same quality as those made from untreated grain.
"We wanted to determine if the grain looked any different; if it milled
the same way; if it made flour the same way. Does bread taste the same
when made from ozonated wheat?" Mason said. "Essentially, there were no
differences. The food industry can take grain that's been treated with
ozone and know it won't affect their ability to come up with the same
products in the end."
The team also checked how ozone treatments affected amounts of important
amino acids and essential fatty acids, fats not produced by the body.
The treatments caused no significant difference in any of the
nutritional and metabolic values of these substances in any of the
grains studied, Mason said.
The scientists began their study after a company that uses ozone air
purification systems in hospitals noticed that air vents were cockroach
free. Absence of cockroaches in a large building is unusual, so the
researchers tested various ozone doses on different insects and found
the gas was fatal to bugs.
"All the species we tested seemed affected," Mason said. "The only ones
we don't have control over are immature weevils since they are hidden
within the kernels. Ozone, unlike chemical fumigants, doesn't penetrate
into the kernel enough to kill immature insects."
Currently, the researchers are studying ways to use ozone as a
preventative treatment by possibly sealing of grain storage facilities
with layers of ozone, much the way a jelly jar is capped with wax.
The USDA National Research Initiative provided funding for this study.