Issue Date: September 8, 2008
Irradiation Of Lettuce & Spinach
IN THE WAKE OF numerous outbreaks of food-borne illness over the past two years, the Food & Drug Administration announced in August that it will allow the irradiation of fresh iceberg lettuce and spinach to kill bacteria such as Escherichia coli O157:H7 and Salmonella enterica. The food industry and Congress welcomed the move, but some food safety experts warn that the technology will rob food of essential nutrients and create a disincentive for growers and food handlers to clean up their acts.
The decision to allow irradiation of iceberg lettuce and spinach comes after years of debate. Since 1999, FDA has been considering a petition from a coalition organized by the Grocery Manufacturers Association (GMA) to allow irradiation—zapping food with low levels of ionizing radiation—of fresh produce and other ready-to-eat foods.
"After letting a petition that would allow irradiation on fresh fruits and vegetables languish for more than eight years, I am happy to hear that FDA has finally acted and approved irradiation for use on fresh lettuce and fresh spinach," said Rep. John D. Dingell (D-Mich.), chairman of the House Energy & Commerce Committee, in a statement.
Dingell urged FDA "to take quick action and approve irradiation for use on other fresh produce and ready-to-eat foods." Since January 2007, the House Energy & Commerce Committee has held nine hearings on the safety of the U.S. food supply.
In the U.S., irradiation has been used primarily to kill pathogens on ground beef, poultry, and spices. Lettuce and spinach now join this group of approved foods that can be treated by irradiation. The ionizing radiation used to treat food is either in the form of gamma rays generated by the radioactive isotope cobalt-60, electron beams generated by a linear accelerator, or X-rays produced by allowing an electron beam to strike a metal alloy.
Although FDA does not differentiate between the three ways of generating ionizing radiation, the public is more likely to accept food irradiation if it does not involve the use of a radioactive isotope, says Suresh Pillai, director of the National Center for Electron Beam Research at Texas A&M University.
"Electron beam is probably where the future lies because it does not involve any radioactive isotope," Pillai tells C&EN. It's not because irradiation using cobalt-60 has been shown to be unsafe, but rather because radioactive isotopes, in addition to having a negative public image, are expensive to procure, store, and dispose of, he explains.
Regardless of the source of ionizing radiation, FDA considers food irradiation to be safe and has approved the technology for a handful of foods. But market acceptance of the technology has been very low, says Bill Freese, science policy adviser at the nonprofit Center for Food Safety. Concerns include the high cost of the technology, the potential to form dangerous chemicals and free radicals in treated foods, and the possibility of depleting nutrients. Still others worry about the flavor and texture of foods subjected to irradiation.
MANY RESEARCHERS, however, are optimistic that FDA's decision to allow irradiation of fresh lettuce and spinach will give the technology the boost it needs to gain wider acceptance.
According to Pillai, FDA's new rule allows high-enough radiation levels to kill many bacteria as well as many viruses on fresh lettuce and spinach. The FDA-approved level is up to 4 kilograys (kGy) of ionizing radiation on these products.
Pillai notes that his group is currently determining the lowest dose needed to destroy food-borne viruses such as norovirus, hepatitis A, and polio. "We are trying to reduce the dose because it makes the process cheaper and takes less time," he says. "Even at 1.5- or 2-kGy doses, you can achieve safe products."
Some food safety experts, however, aren't convinced that irradiation of fresh produce is a good idea, emphasizing that the technology will distract attention from unsanitary conditions and decrease levels of some nutrients. "Irradiation is no substitute for measures to clean up the huge animal operations that pollute our waterways and irrigation water with the raw manure that often carries pathogenic bacteria," Freese said in a statement. According to Freese, scientific studies have shown that irradiation can dramatically lower amounts of nutrients, such as vitamin A and folate, both of which are found at high levels in spinach.
FDA acknowledges that irradiation does lead to the loss of some vitamins, but the agency concludes in a Federal Register notice that a maximum dose of 4 kGy on fresh spinach and iceberg lettuce "will not have an adverse impact on the nutritional adequacy of the overall diet." In other words, irradiation will diminish the nutrient content of spinach, but because spinach contributes at most 3.5% of the total vitamin A intake and just over 2.0% of the total folate intake in a typical U.S. diet, FDA concludes that it will not have an adverse impact on a person's overall diet.
But Freese believes that FDA's analysis is misleading. "There are a lot of people who don't eat much spinach or any at all. Others eat quite a bit of it. You've got to consider subpopulations that eat higher percentages of certain foods," he emphasizes. Instead, he explains, FDA based its calculations on averages.
SOME CRITICS also question how the U.S. will build an infrastructure of facilities to support the irradiation of significant quantities of fresh lettuce and spinach. Approximately 9 billion lb of lettuce and 1 billion lb of spinach are consumed annually in the U.S., according to the nonprofit Food & Water Watch. "There is no system in place to irradiate large amounts of perishable vegetables and deliver them to market. Today, only two commercial irradiation facilities specifically designed to irradiate food are in operation," Wenonah Hauter, executive director of Food & Water Watch, said in a statement.
Hauter echoes the concerns of Freese and others who say that irradiation will mask unsafe practices used by the food industry. Food & Water Watch has pushed for years to overhaul the U.S. food production system.
Nonetheless, those in favor of food irradiation hope that it will soon be allowed on other produce. As you lower the dose, more varieties of produce become amenable to the technology, Pillai says. "There has been a lot of work on irradiation of tomatoes, peppers, cilantro, and parsley, all of which are very vulnerable to microbial contamination," he adds.
No matter what FDA decides about other produce, nearly everyone agrees that irradiation is not a silver bullet. "This technology should not be used by itself. It should be used in conjunction with other steps at the farm, during packaging, even at home," Pillai emphasizes.
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