Zapped greens enter the fray
For many consumers, the prospect of eating produce zapped with ionizing radiation doesn’t sound all that appetizing, conjuring up images of mushy fruits and wilted leaves -- not to mention fears over safety. Last month’s ruling by the Food and Drug Administration that food manufacturers can now irradiate fresh spinach and iceberg lettuce to kill bacteria came with reassurances that the process wouldn’t result in food any less appealing or healthful than non-irradiated varieties.
Research indicates that that may all be true. But critics say the new rule ignores the source of the problem -- sloppy agricultural practices -- and could give consumers a false sense of security.
One might imagine that washing would take care of most bacteria on a piece of fresh fruit or a vegetable -- including the forms of E. coli and salmonella implicated in recent food-borne disease outbreaks. But the microbes that spurred the Washington, D.C.-based Grocery Manufacturers Assn., an industry group, to request the current ruling are known as internalized bacteria -- so called because they’ve taken up inside the plant’s tissues and can’t just be washed off under the faucet.
Food irradiation, on the other hand, does penetrate deep. The process uses high-energy particles, usually in the form of gamma rays (generated by radioactive cobalt) or electron beams (similar to those in a television set). The particles break up water molecules in the plant, which then release free radicals that damage cell walls and DNA of any reproducing bacteria nearby.
Contrary to popular perception, the food doesn’t retain radiation any more than, say, skin does after a day in the sun -- which is to say, not at all. It heats up a bit during treatment, then the radiation dissipates -- and no radioactive compounds enter the food.
When the radiation dose is kept low enough, the plant’s own cells remain largely intact. When it’s too high, however, the whole plant suffers. Irradiated food’s reputation suffered a blow half a century ago, says Brendan Niemira, acting research leader with the U.S. Department of Agriculture’s in Wyndmoor, Penn. Early experiments to develop an eternally shelf-stable head of lettuce resulted in leaves that were limp, colorless and bland.
Back then, scientists were dosing food with up to 10 grays of radiation. (A gray is a measure of how much energy is absorbed: It corresponds to one joule of energy per kilogram of matter.) The FDA’s new rule allows food manufacturers to dose spinach and iceberg lettuce with up to 4 grays, enough to kill germs without withering plant material.
The agency already allows food makers to irradiate meat, poultry, spices and some types of shellfish. In fact, irradiation is widely used on the spices in processed foods, said Anuradha Prakash, professor of food science and nutrition at Chapman University in Orange. (Irradiated whole products, such as ground beef, must bear an internationally recognized symbol, known as the radura, or state that they’ve been treated with radiation.)
The recent decision to expand irradiation to lettuce and spinach was based in part on studies demonstrating irradiation’s effectiveness at killing harmful microbes. For example, Niemira’s studies, which focused on spinach and lettuce, showed that irradiation was up to four times as effective at ridding the greens of internalized E. coli when compared with washing with water or a chlorine solution. He also showed that irradiation is particularly effective at reducing the amount of E. coli stored up in iceberg lettuce.
But critics argue that effectiveness aside, irradiation has unwanted side effects -- including the creation of chemicals such as furans and 2-alkylcyclobutanones, which may be toxic in very high doses, and the destruction of vitamins and minerals. Furthermore, says Bill Freese, science policy analyst with the Washington, D.C.-based advocacy group Center for Food Safety, “food irradiation masks the unsanitary conditions of industrial agriculture.”
Irradiating food can create chemical changes in food, but these are little different from the chemical changes yielded by processing, Prakash says. Compounds such as furans are also generated by cooking, she says. Ones unique to irradiated foods, such as 2-alkylcyclobutanones (which in some studies, but not others, have been shown to damage DNA) are generated at very low levels. Decades of animal feeding tests, Prakash adds, suggest that irradiated foods don’t contain levels of chemicals that pose any risk to health.
Decades of testing have also shown, however, that dosing food with gamma rays or electron beams can destroy vitamins and minerals, including vitamin C and thiamine. The FDA’s rule acknowledged that irradiation can reduce levels of vitamin A and folate in spinach. One study, for example, showed that irradiating fresh spinach with 2.5 grays of radiation led to a 10% loss in folate levels. But because fresh spinach isn’t a major source of these two vitamins in the average American diet -- that is, because most Americans don’t eat much of the stuff -- the agency concluded that irradiation would “not have an adverse impact on the nutritional adequacy of the overall diet.”
“It’s deceptive,” Freese says. “An irradiated product looks normal but has invisible reductions in vitamins and nutrients.”
Freese says that the source of bacteria in food-borne outbreaks is often traced to farms where livestock are raised in crowded, unsanitary conditions, and that the current ruling does nothing to address this. “It’s an attempt to fix the problem at the end of the line, instead of going to the source,” he says.
The Grocery Manufacturers Assn., which has also asked the FDA to rule on irradiating other types of lettuce, as well as tomatoes, carrots and cabbage, considers irradiation a valuable tool. “It’s the best and only step [in the production process] to ensure a pathogen-free product,” says Brian Kennedy, the association’s director of communications.
But irradiation, though it could cut down significantly on internalized bacteria, is no guarantee that spinach and iceberg lettuce will be 100% pathogen-free. The technology’s effectiveness depends on the amount of bacteria in the plant to begin with, Niemira says. The greater the starting number of bacteria, the more likely that some will remain after treatment.
And though it takes hundreds of millions of E. coli bacteria to make a person sick, in the case of salmonella, it takes only a handful. That means irradiation will never be a substitute for clean farming practices.
Pathogen-free produce is certainly an enviable end point -- but, Niemira says, “zero is a hard thing to achieve.”