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IrradiationAn Overview of a Safe Alternative to
Fumigation
It passes through food in the form of radiant energy, without leaving
any residue. Ionizing radiationthat which produces enough energy to kill
bacteria and other pathogens in foodinvolves the use of gamma rays
produced by cobalt or cesium, or x rays. The Food and Drug
Administration (FDA) has declared that low-dose irradiation of food
presents no health risk.
In the 1920s, a French scientist
discovered that irradiation could preserve food. During World War II, the
U.S. Army tested irradiation on fruits, vegetables, dairy products, and
meat. Irradiated food has been routinely used for years by NASA.
Donald W. Thayer, a research chemist with USDA's Agricultural Research
Service, and colleagues at ARS' Food Safety Research Unit of the Eastern Regional Research
Center in Wyndmoor, Pennsylvania, have been testing irradiation on
food for 16 years.
Not only does irradiation extend
the shelf life of fruits and vegetables, but it also kills pests. And,
unlike methyl bromide, irradiation does not adversely affect the
environment. Thayer likens irradiation to pasteurization. "When used with
the proper handling and processing techniques, irradiation greatly reduces
the risk that contaminated meat, poultry, and other foods will reach
consumers."
Methyl bromide, which will be banned on January 1,
2001, is the primary fumigant that now allows fruits, vegetables, and
grain to be transported across state lines and exported to other
countries. Irradiation can serve the purposesafely, economically, and
effectivelyfor many of these commodities.
"Irradiation reduces the
chance of foodborne pathogens reaching the consumer," says Thayer.
"Scientific studies conducted worldwide over the past 40 years have shown
irradiation to be a wholesome process."
According to Thayer,
during the irradiation process, food never comes in contact with any
radioactive material. The gamma rays, x rays, or electrons used in the
process do not make food radioactive. Irradiation, he says, is similar to
exposure to sunlight or being x-rayed for medical reasons. Specific doses
of radiation can kill rapidly growing cells, such as those of insects or
spoilage, and pathogenic bacteria. But the process has little effect on
the food itself because there is no cellular activity in the food. The
changes that do occur are similar to the effects of canning, cooking, or
freezing food.
One concern that has been raised with irradiation is
that it may affect the nutritional aspect of food. Thayer reports that
irradiation can minimally affect some very sensitive vitamins like
B1 in
pork.
"But it has been estimated that if all the pork
in the United States were to be irradiated, Americans would lose only 2.3
percent of the vitamin B1 in their diets," Thayer says.
"Irradiation
converts small amounts of vitamin C in fruit to another equally usable
form, so nothing is lost. In fact, multigenerational studies of animals
fed irradiated foods show that not only is it safe, but the nutritive
value remains virtually unchanged."
Herbs, spices, and
seasonings can introduce bacteria that may cause spoilage or foodborne
disease in food which must be stored or transported before reaching
consumers. Some commercial food processors treat spices with methyl
bromide to kill insects or with ethylene oxide to control bacteria and
mold. Both of these chemicals are extremely toxic.
But most
spices, herbs, and dry vegetable seasonings in the United States are
treated with ionizing radiation, which was sanctioned for this particular
use by FDA in 1986.
In 1963, FDA authorized the first use of
irradiation to treat food in the United States. Wheat and wheat flour
were irradiated to rid them of insects. An electron beama result of
collaborative research between ARS and the U.S. Armyis used to kill
insects on about 400,000 tons of wheat a year at the port of Odessa,
Ukraine. This irradiation treatment is not used in the United States
because for the time being we have other fumigants and methods of getting
pests out of grain.
It was 23 years later, in 1986, that
irradiation was approved to control insects and inhibit growth and
ripening in fruits, vegetables, and grain. Irradiation increases the
shelf life of very perishable sweet onions to 3 months and not only
extends the shelf life of tomatoes, but also allows them to be picked when
fully ripe. Most flavorless tomatoes taste that way because they're
picked green to ensure they get to market before they rot. Zapped by
irradiation, mushrooms can last for 3 weeks without browning or cap
separation and strawberries can stay in the refrigerator for 3 weeks
without decay or shrinkage.
Even the dreaded Cyclospora
parasite succumbs to irradiation. Thayer and colleagues have
completed four studies of this pest, which has recently been found on
raspberries and strawberries.
"We used a dose of
irradiation that is recommended for fresh fruit on raspberries infected
with Cyclospora. Not only did the irradiation inactivate the
parasite, but it also doubled the raspberries' shelf life," Thayer
reports. "More research is planned on irradiating Cyclospora, but
it reacts in much the same way as Toxoplasma gondii, a species of
organism that continues to sporulate after irradiation but does not
multiply in its host."
Most of Thayer's irradiation
work has been with meat to rid it of harmful microorganisms that cause
foodborne illnesses. He was the first to discover that E. coli
0157:H7 could be controlled by radiation, and he and colleagues have
successfully used irradiation against other foodborne pathogens including
Bacillus cereus, Clostridium botulinum, Listeria monocytogenes,
Salmonella, Staphylococcus aureus, and Toxoplasma
gondii on meat and poultry. FDA's 1990 approval to use irradiation on
poultry to eliminate harmful pathogens was, in part, a result of Thayer's
research, as is the pending petition for approval to irradiate red
meat.
In addition to USDA scientists and FDA, the list of endorsers
of irradiation includes the U.S. Department of Health and Human Services,
U.S. Public Health Service, U.S. Army, National Association of State
Departments of Agriculture, American Medical Association, American
Dietetic Association, American Meat Institute, Institute of Food
Technologists, and National Food Processors Association. The World Health
Organization and the Codex Alimentarius Commission sanction the use of
irradiation, which is also being used in about 40 other countries.
"A safe, effective alternative to methyl bromide, irradiation has no
harmful side effects," Thayer says.
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Last Updated: October 22, 1997
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