BACKGROUNDER: Food IrradiationBy
The Food and Drug
Administration on Dec. 2 approved irradiation to control
microorganisms on fresh and frozen red meats including beef, lamb and
pork. This FDA approval--and some previous ones--were based partly on
research by chemist Donald W. Thayer of USDA's
Following is an overview of irradiation and some of Thayer's
findings over the years. For example, he was the first to discover
that irradiation could control the meat-contaminating pathogen E.
coli 0157:H7. He has also found that irradiation kills the Cyclospora
parasite on raspberries and strawberries.
Irradiation: An Overview
Irradiation passes through food in the form of radiant energy,
without leaving any residue. Ionizing radiation--that which produces
enough energy to kill bacteria and other pathogens in food--involves
the use of gamma rays produced by cobalt or cesium, or X-rays or
electrons from machine sources. The Food and Drug Administration has
declared that low-dose irradiation of food presents no health risk.
In the 1920's, 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 the National
Aeronautics and Space Administration.
Donald W. Thayer, a research chemist with USDA's
Service, and colleagues at ARS'
Safety Research Unit of the
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. 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,"
"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
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
One concern 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 3.2 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 that 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 these chemicals are extremely
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 beam--a result of collaborative research
between ARS and the U.S. Army--is 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
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 three 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 three weeks without browning or cap separation
and strawberries can stay in the refrigerator for three weeks without
decay or shrinkage.
Even the dreaded Cyclospora parasite succumbs to
irradiation. Thayer and colleagues have completed four studies of this
pest that 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 does
irradiation inactivate the parasite, but it also doubles 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
FDA's 1990 approval to use irradiation on poultry to eliminate
harmful pathogens was, in part, a result of Thayer's research, as was
the Dec. 2, 1997, 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,
Dietetic Association, American
Meat Institute, Institute of Food Technologists, and
Processors Association. The World
Health Organization and the Codex Alimentarius Commission
sanction the use of irradiation, which is also being used in about 40
Scientific contact: Donald W. Thayer, USDA, ARS '
Safety Research Unit, Wyndmoor, Pa., phone (215) 233-6582, fax
(215) 233-6406, email@example.com.
This backgrounder was adapted from an article in the October 1997
issue of ARS' Methyl
Bromide Alternatives newsletter. The article is on the World
Wide Web at: