Irradiation Almost Erases Risk of Food Poisoning

By Steven Reinberg
HealthDay Reporter
Thursday, April 10, 2008; 12:00 AM

THURSDAY, April 10 (HealthDay News) -- Washing fresh fruits and vegetables can reduce the risk of food poisoning, but only irradiation kills almost all disease-causing bacteria, new research shows.

The study suggests that irradiation, which is currently being reviewed by the U.S. Food and Drug Administration, can kill bacteria that are beyond the reach of conventional chemical sanitizers, including inside the leaves of spinach and lettuce.

"If you have pathogens that are inside a leaf, then normal chemical sanitizers are not going to be able to kill those very effectively," said lead researcher Brendan A. Niemira, a microbiologist with the United States Department of Agriculture at the Agricultural Research Service in Wyndmoor, Pa.

"What I have demonstrated is that pathogens that are inside a leaf are killed by radiation," Niemira said. "This is something that has not been demonstrated before."

"The spinach outbreak in the fall of 2006, in particular, raised questions about how these organisms survived the various treatments that are applied -- the rinses and the washes and things, Niemira noted in a statement.

In addition, Niemira looked at pathogens that are protected inside a biofilm. Pathogens form complex communities on the surfaces of leaves called biofilms, he explained. "Once they are inside these biofilms, they are very difficult to kill."

In irradiation, food is exposed to electronic beams that create positive and negative charges. This process disrupts cell-destroying pathogens such as E. coli and salmonella, as well as insects.

Irradiation is used to kill bacteria and insects to extend the shelf life of food, for example, by delaying the ripening of fruits or the sprouting of vegetables. Irradiated foods, except for spices, must be labeled as such, according to the FDA. The FDA has been considering whether to approve irradiation to prevent the spread of harmful bacteria since 1999, Niemira noted.

The USDA researchers presented their findings Thursday at the American Chemical Society annual meeting, in New Orleans.

In their study, Niemira and his colleagues found a way to draw bacteria into the leaves of leafy green vegetables. The vegetables were then treated either with a three-minute water bath, three minutes of chemical treatment, or irradiation.

The researchers found that washing with plain water did not reduce bacteria levels in spinach or lettuce. Chemical treatment did not significantly reduce E. coli in spinach leaves and was less than 90 percent effective when it came to removing E. coli from lettuce.

Irradiation, however, reduced the level of E. coli by 99.99 percent in lettuce and by 99.9 percent in spinach, the researchers found.


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