In the wake of Europe's recent E. coli outbreak, in which sprouts contaminated with a particularly vicious strain killed 36 people and sickened thousands, food safety officials are asking once again what more can be done to curb the spread of food-borne illnesses.
Food-borne infections in the U.S. have declined 20% over the last 10 years, thanks to tighter regulations and steps taken by the food and agricultural industries, according to the Centers for Disease Control and Prevention. But they still cause more than 48 million cases of illness and about 3,000 deaths each year.
Some experts say part of the solution lies with food irradiation — an effective, underused method of prevention that's been around for more than 100 years.
Food irradiation involves treating items with low-dose X-rays, electron beams or gamma rays. The high-energy particles in the rays and beams kill disease-causing pathogens such as E. coli and salmonella by damaging their genetic material. The particles also break up water molecules in the food, releasing free radicals that can kill bacteria and parasites.
No radioactive materials end up in the food itself, even though in the case of gamma rays the source is radioactive cobalt, said food irradiation expert Christine Bruhn, director of the Center for Consumer Research at UC Davis. Electron-beam and X-ray irradiation involve no radioactive elements, Bruhn added.
But widespread fears about nuclear radiation in the 1950s led Congress to require the Food and Drug Administration to regulate irradiation as a food additive instead of a treatment process. As a result, all irradiated food has to bear a label. (The exceptions are irradiated food sold in restaurants, and cases when the whole food item hasn't been irradiated but ingredients like spices have been.)
In the 1960s, the FDA approved irradiation to prevent mold growth in wheat flour and sprouting in potatoes; in the 1980s, the agency added pork and produce to the list to kill the food-borne pathogen trichinosis (in pork) and insects (on produce). Irradiation is also approved to kill pathogens in raw oysters, red meat, poultry, shell eggs, sprouts, spinach and iceberg lettuce. (Food consumed by astronauts on long trips to space is also often irradiated to extend shelf life.)
But because manufacturers have been reluctant to proclaim the treatment to consumers, irradiation hasn't been widely used.
The top use of irradiation in the U.S. is to treat spices used by the food industry; 175 million pounds of spices — a third of the spices used in commercial production — are irradiated, said Ronald Eustice, national director of the Minnesota Beef Council and a consultant to the Food Irradiation Processors Alliance.
A smaller fraction of the meat supply is irradiated: about 18 million pounds of meat and poultry, or less than half of 1% of the total. Among produce, irradiation is used mostly to kill insects on imported tropical fruits, such as mangoes, guavas and papayas. Each year, 35 million pounds of tropical produce are irradiated.
Because irradiation penetrates food, the process can kill pathogens that have been taken up into seeds or plants. That makes it useful for eliminating germs that can't be addressed by washing produce in the kitchen sink, said food irradiation researcher Rosana Moreira, a professor in the department of biological and agricultural engineering at Texas A&M University in College Station.
Not all foods can be irradiated, Moreira added. Some high-fat foods, such as milk and cheese, can acquire off-flavors after the treatment.
And even though meats and produce can be irradiated, the dose must be calibrated just right so that the rays penetrate the entire food. With irregularly shaped foods, such as a mango or a head of broccoli, that can be a challenge. If the dose is too low, pathogens may remain in the food. If the dose is too high, it can cause pitting, bruise-like marks, damage to a fruit's skin, off flavors and reduced shelf life.
Despite these technical challenges, food irradiation has great potential to prevent food-borne illnesses, experts said. If used on fresh produce, spices and grains, it could cut down significantly on pathogens such as E. coli, salmonella and shigella, Moreira said. On ready-to-eat meats, such as frozen hamburgers, hot dogs and deli meats, it can virtually eliminate any contaminating bacteria, Bruhn added. (Because of their regular shapes, such products are easy to irradiate evenly and thoroughly.)