Irradiation Gets Shot In the Arm

Scientists at the USDA suggest that irradiation can kill pathogens that are beyond the reach of conventional chemical sanitizers used on farms.

The first issue of Miller-McCune magazine looked at the industry and government response to the E. Coli outbreak of 2006, in which tainted spinach sickened more than 200 people and killed three.

Industry groups have drafted a marketing agreement that would effectively sterilize farms by eliminating perimeter hedgerows and wildlife; smaller farmers have lobbied for regulations on the bagged greens produced by large industrial farms, which, according to the U.S. Department of Agriculture, account for 98.5 percent of E. coli O157:H7 illnesses tied to California's leafy greens since 1999.

As the article outlined, another possible solution — although one rarely raised by farmers in the United States — would be irradiation. Now, new findings from scientists at the USDA suggest that irradiation, which is currently being reviewed by the FDA, can kill pathogens that are beyond the reach of conventional chemical sanitizers.

"When bacteria are protected — whether they're inside a leaf or inside a biofilm — they're not going to be as easy to kill," says Brendan A. Niemira, a microbiologist with the USDA's Agricultural Research Service in Wyndmoor, Pa., who directed the study, which was presented yesterday during the 235th national meeting of the American Chemical Society. "This is the first study to look at the use of irradiation on bacteria that reside inside the inner spaces of a leaf or buried within a biofilm."

In the study, the scientists chopped up leaves of romaine lettuce and baby spinach and dunked them in a cocktail of E. coli. The bacteria was pushed inside the leaves, which were then treated with either a three-minute water wash, a three-minute chemical treatment, or irradiation. The results showed that washing with plain water did not reduce the levels of the pathogen on either spinach or lettuce. The chemical treatment, a sodium hypochlorite solution, did not significantly decrease the number of E. coli cells in spinach leaves, and reduced the E. coli less than 90 percent on the romaine lettuce.

Ionizing radiation, in contrast, significantly reduced the pathogen population in both the spinach and the lettuce leaves, with reductions of 99.99 percent on romaine lettuce and
99.9 percent on spinach at the highest dose tested. The scientists will also test how irradiation might work on plants in the field.

Of course, a process that exposes food to electron beams, disrupting the genetic material of living cells, will never be popular with everyone. But Christine Bruhn, who studies consumer issues in food safety and quality at the University of California, Davis, says consumers have developed more confidence in the technology as its ability to reduce pathogens has become more well known. "Sixty to 90 percent of consumers indicate that they would buy irradiated food when told of the benefits of the process and the endorsement of health authorities," Bruhn says.

She and Niemira have submitted a proposal to the USDA to further explore irradiation of leafy greens and to better gauge public opinion about the technology.

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