January 2009 Issue

Irradiation: What It Is, What It Does, and How It Affects the Food Supply
By Sharon Palmer, RD
Today’s Dietitian
Vol. 11 No. 1 P. 32

It may hold the power to help solve the world’s food safety problems, but are there any hidden costs to this high-tech solution?  

Food irradiation is today’s pasteurization. In the early 1900s, pasteurization wiped out rampant milk-borne diseases such as typhoid fever, scarlet fever, and diphtheria, but some people were concerned about its effects on milk quality and sanitary conditions in dairy processing. Today, food irradiation has the capacity to significantly decrease the food-borne illnesses of our age, including Escherichia coli and Salmonella. Yet, suspicions have arisen as many people wonder what the technology actually involves and whether it will negatively effect the quality and safety of their food.  

What Is Food Irradiation?   
According to the Centers for Disease Control and Prevention (CDC), irradiation is a safe and effective technology that has the potential to prevent many food-borne diseases. Treating raw meat and poultry with irradiation at the slaughter plant can reportedly eliminate bacteria such as E. coli O157:H7, Salmonella, and Campylobacter, organisms that cause millions of infections and thousands of hospitalizations annually in the United States. Irradiating raw meat can also eliminate Toxoplasma organisms responsible for severe eye and congenital infections. Irradiating prepared, ready-to-eat meats such as hot dogs and deli meats can eliminate the risk of Listeria. Irradiation can also eliminate bacteria such as Shigella and Salmonella from fresh produce, treat dry foods such as spices and grains that may be stored for long periods of time and transported over great distances, and treat animal feeds that may be contaminated with bacteria.

“Irradiation is a technology that leaves no residue in food products and destroys the DNA of microorganisms to prevent them from multiplying. When you irradiate food, you produce an effect on microorganisms due to their effects on DNA and cell membranes. Photons, electrons, or x-rays strike the cell membranes and the DNA, damaging both. In plant cells, DNA is not required for reproduction, so damage to DNA is irrelevant. But in bacterial cells, DNA is essential for multiplication. When energy strikes the DNA and the single-strand or double-strand breaks occur, the DNA is too damaged and can’t repair itself, so the cell dies,” explains Anuradha Prakash, PhD, a professor and the program director of food science at Chapman University in Orange, Calif., and an Institute of Food Technologists spokesperson.

There are three irradiation technologies that rely on three kinds of rays: gamma rays, electron beams, and x-rays. Gamma ray technology uses the radiation given off by the radioactive form of Cobalt-60 or Cesium-137 to produce high-energy photons called gamma rays, which can penetrate foods to a depth of several feet. Since these substances do not give off neutrons, they do not make anything around them radioactive. This kind of technology has been at work for more than 30 years for sterilizing medical, dental, and household products and treating cancer. During food irradiation, the substance is pulled into a chamber with massive concrete walls that keep any rays from escaping, so the food is exposed to the rays for a defined period of time.            

The electron beam is a stream of high-energy electrons propelled from an electron gun, a larger version of the device in the back of a TV tube that propels electrons into the screen. This electron beam generator is simply switched on and off and does not involve radioactivity. Shielding is necessary to protect workers from the electron beam but not in the form of the massive concrete walls required to contain gamma rays. The electrons can penetrate food to a depth of only 3 centimeters, but two opposing beams can treat food that is twice as thick. Electron beam medical sterilizers have been in operation for the past 15 years. 

The latest technology is x-ray irradiation, which employs a more powerful version of the x-ray machines used in hospitals and dental offices. A beam of electrons is directed at a thin plate of gold or other metal, producing a stream of x-rays that come out the other side. X-rays can pass through thick foods and require heavy shielding for safety. The machine can be switched on and off and does not involve radioactive substances. Since 1996, the world has seen four commercial x-ray irradiation units. The radiation dose varies depending on the type of food. According to the Environmental Protection Agency, the limit is less than 10 kiloGray for most foods. The FDA sets radiation dose limits for specific food types, such as 1 kiloGray for fruit, 3 kiloGray for poultry, and 30 kiloGray for spices and seasonings.

Overcoming Consumer Confusion
“I think the biggest barrier for food irradiation is lack of consumer understanding of what irradiation is. Perhaps it was an unfortunate choice of names for this technology, as people have the impression that there is a nuclear source making their food radioactive,” says Prakash.

Samuel S. Epstein, MD, professor emeritus of environmental and occupational medicine at the University of Illinois School of Public Health and chairman of the Cancer Prevention Coalition, says consumers simply don’t know enough about food irradiation in general. After all, it’s not a topic people typically read about in their favorite glossy magazine. The International Food Information Council studied media coverage of food irradiation from January 1, 2004, to February 29, 2004, and discovered that the total amount of media coverage was a mere 35 stories. 

Food irradiation, also known as cold pasteurization, is not a new technology. The idea of using irradiation to destroy microorganisms in food may have emerged as early as 1895, soon after radioactivity was discovered, according to researchers from the University of Texas School of Public Health. In 1963, the FDA approved irradiation to control insects in wheat and wheat flour and has studied food irradiation’s effects for more than 40 years. About 40 countries use the technology, and many organizations, including the CDC, the World Health Organization (WHO), the USDA, the FDA, the American Dietetic Association, and the American Medical Association, endorse it. Yet, consumer acceptance of food irradiation has been elusive, consumer advocacy groups battle the technology, and its use in the United States is minimal.           

Opponents and environmental and consumer advocacy groups have stepped forward with claims that food irradiation poses safety concerns, affects food quality, causes nutrient loss, and threatens the environment. “The effects of negative activist groups is quite strong. People hear things from activist organizations, and it decreases the consumer acceptance a lot,” says Prakash, who points out that some studies have found that consumers are willing to pay for irradiated food products once the benefits have been fully explained to them. A 1995-1996 University of California, Davis study found that after consumers viewed a 10-minute informational video on irradiation, their interest in buying irradiated foods increased from 57% to 82%.

Irradiation in the Food Supply
Food irradiation is getting more attention in light of the August 22, 2008, FDA final rule allowing irradiation of fresh iceberg lettuce and spinach in both loose and bagged forms. The FDA reported that irradiating fresh iceberg lettuce and spinach will help protect consumers from disease-causing bacteria such as Salmonella and E. coli O157:H7. In addition, irradiating fresh iceberg lettuce and fresh spinach will lengthen their time to spoiling.             

The FDA ruling adds iceberg lettuce and spinach to a list of other foods that are permitted to be irradiated to control bacteria and prolong freshness, including wheat flour, fruit, potatoes, red meat, poultry, and spices (see Table 1). But currently, the volume of food being irradiated in the United States is low. Prakash reports that these foods include about 1% to 2% of ground beef, some dried spices and herbs, fruit from Hawaii such as star fruit and papaya, and strawberries from Florida.   

One detractor from more widespread use of irradiation is cost. “The cost depends on how much is treated and at what dose. The higher the volume, the lower the cost due to efficiencies of scale. The additional cost for irradiation could be 3 to 10 cents per pound,” says Prakash.          

In addition, there are a limited number of irradiation facilities available, adding yet another chink in the chain of food processing. “There are not too many facilities that can process produce. There may have to be different scenarios such as portable technology or units in large facilities that can be part of the food processing. It is likely suitable for foodservice,” notes Prakash.

Looking to the Label
The FDA regulates sources of irradiation the same way that it regulates food additives; thus, they require approval before being allowed for use on the market. Irradiation is voluntary, and the FDA requires that treated foods bear the Radura logo along with the statement “treated with radiation” or “treated by irradiation.” Irradiation labeling does not apply to restaurant foods, and organic foods can not be irradiated. 

In 2007, the FDA proposed revising its labeling regulation for foods approved for irradiation. According to Consumer Affairs, under the proposed new rule, only irradiated foods in which the irradiation causes a material change in the food’s molecular structure would need to be labeled with the Radura logo, which is currently required of all irradiated food. In addition, the FDA would permit the terms electronically pasteurized or cold pasteurized in lieu of irradiated if notified that the irradiation process being used met the criteria specified for using the term pasteurized.     

Some claim that this proposed ruling would weaken the irradiation labeling laws. Epstein says, “Due to strong industry pressure, the FDA is attempting to get rid of irradiation for the term ‘electronically pasteurized.’ If this euphemism is successfully used, it limits the public’s perception of foods being irradiated.” The Center for Science in the Public Interest reports that, according to polls, consumers want clear information about whether their foods have been irradiated.

How Safe Is Food Irradiation?
Many leading health organizations have deemed food irradiation safe, likening it to the pasteurization of milk and pressure cooking of canned foods, processes that kill harmful bacteria and parasites. Even astronauts are fed irradiated food to prevent food-borne illness while in space. In a May 2008 review published in Critical Reviews in Food Science and Nutrition, researchers from the University of Arkansas reported that more than 100 years of food irradiation research has demonstrated that it would make food safer and improve shelf life. Though the CDC reports a significant drop in the number of food-borne illnesses, contaminated food still causes too many sicknesses and deaths. The researchers concluded that new and underutilized technologies such as food irradiation need to be reexamined to enhance the safety of the food supply.

Yet, some critics point out that the safety of this technology may not be crystal clear, expressing concern about carcinogens, radiolytic compounds, and furans. “There are a wide range of independent studies done in the mid- to late 1980s that identified mutagenic and carcinogenic compounds. In irradiated meat, there is a tenfold increase in the carcinogen benzene than in cooked beef,” says Epstein. According to Melinda Hemmelgarn, MS, RD, a columnist and Food and Society Policy fellow who recently wrote a column on food irradiation in the Columbia Daily Tribune and for the Rodale Institute, “Valid concerns have been voiced about the production of free radicals or the formation of other potentially harmful compounds during the radiation process.” Some experts believe that we don’t have any long-term studies of populations eating significant amounts of irradiated food to make conclusions.

“Irradiation does not produce compounds that are mutagenic. There are extensive toxicological studies performed, and there is no evidence that there are mutagens or carcinogens formed because of irradiation. The WHO and the FDA have rejected the idea that irradiation produces mutagenic or carcinogenic compounds,” says Prakash. “The activist organizations claim that radiation forms unique radiolytic compounds. One type of radiolytic compound is 2-ACB [2-alkylcyclobutanone] that can be produced in small amounts in fat-containing foods, and it takes high levels of irradiation to do that. Other compounds bandied about are furans. These are produced in foods containing sugar and acid, such as fruit juice. If you irradiate pineapple juice, you get increased furans but not as much as you get during heat processing. Furans, in general, are a concern in food, and it’s an issue with the FDA, but in irradiated foods, furans are produced in small amounts.” Evidence does suggest that 2-ACB and furans are carcinogenic. 

Irradiated food is often treated in packaging, raising the issue of whether the technology affects packaging and transfers toxins to food. According to Prakash, this is a legitimate safety concern. She reports that the FDA has evaluated and approved the use of these plastics for irradiation, but additional research needs to explore what happens when chemicals migrate from plastics into food during irradiation.

Quality Is King
The nutritional and sensory quality of irradiated foods is a hot topic. The Organic Consumers Association posits that irradiated fruits and vegetables benefit the packer and grocer, not the farmer or consumer, because the consumer receives an inferior product that appears fresh but has depleted vitamins and enzymes. Some consumer reports have discovered altered taste and texture perceptions with irradiated foods. 

According to the CDC, irradiation does not change a food’s nutritional value. The high-energy ray is absorbed as it passes through the food and gives up its energy. The food is slightly warmed and may taste slightly different after irradiation. At levels approved for use on foods, levels of thiamin are slightly reduced. In a 2007 Journal of Food Protection study, researchers discovered that the effects of irradiation on the quality of frozen peas and corn caused a reduction in ascorbic acid and texture but had no effect on the vegetables’ color, carotenoid content, or antioxidant capacity.          

“Quality of food is related to dose of irradiation. It takes a very high dose to see damage to quality. At levels that destroy E. coli and Salmonella, there is no effect on quality. In general, vitamin loss during food irradiation turns out to be less than with heat processing. It depends on dose levels we use,” says Prakash. “When it comes to destroying enzymes in food, heat kills enzymes, too. It takes very high levels of irradiation to kill enzymes. The doses used for fruits and vegetables do not produce much effect on enzymes.”

Environmental Issues          
Does food irradiation pose an environmental threat? The Nuclear Regulatory Commission oversees facilities that use radioactive sources, and these facilities must demonstrate tight fail-safe measures, extensive and well-documented safety procedures, and worker training. The branch of the FDA that regulates medical x-ray devices monitors electron beam and x-ray sources. No events have been documented that led to exposing the population to radioactivity. Food irradiation facilities do not become radioactive and do not create radioactive waste. Cobalt-60 decays by about 50% in five years, at which time they can be recharged for further use; cesium-137 decays by about 50% in 30 years. Electron beams and x-ray facilities do not involve radioactive substances.      

A larger environmental argument concerns irradiation’s role in food safety. The Center for Science in the Public Interest responded to the FDA ruling on spinach and lettuce by saying that food irradiation should not be mistaken for a cure-all and suggested that the FDA adopt preventive measures starting at the farm level to control food-borne pathogens.

Hemmelgarn noted in her column that “we have to question the larger food system responsible for widespread food-borne illness outbreaks. Irradiation is not a substitute for good agricultural and manufacturing practices or proper handling at home. To get to the root of the problem, we must understand how ground beef, lettuce, spinach, peppers, and tomatoes become contaminated with Salmonella and E. coli in the first place. That’s the philosophy behind HACCP, or hazard analysis and critical control point, regulation. HACCP guidelines call for tracking potential hazards and points of contamination throughout the entire food system, and correcting problems at the source. Because both Salmonella and E. coli are found in animal feces, investigators look at critical points of contamination, including irrigation water, proximity of crops to feedlots, slaughterhouse conditions, and farm-worker sanitation.”

Epstein adds, “When you put cattle into feed lots and feed them grain, they convert E. coli to E. coli O157:H7, which is responsible for food poisoning. You could totally eliminate the question of food poisoning by taking cows out of feed lots and giving them grass a week or so before slaughter. In vegetables, contamination comes from runoff from feed lot facilities.”

The Bottom Line ... for Now
Irradiated foods should be stored, handled, and cooked in the same way as foods that have not been irradiated. They may have a longer shelf life because they have fewer microbes, including those that cause spoilage. Prakash says, “If there is high bacterial content and a bad quality product, irradiation won’t fix the problem. The cold chain and good manufacturing practices must be followed. There is no benefit to start with a poor quality product.            

“We have a pretty safe food supply, but we process a huge volume of food and we have a centralized food supply,” she adds. “Chances of outbreaks are continually going to exist. I fully support the local movement, but people are still going to get lettuce from California in Boston during the winter. Irradiation is another tool to help make our food safer. These products shipped through distribution would be benefited by irradiation.”

— Sharon Palmer, RD, is a contributing editor at Today’s Dietitian and a freelance food and nutrition writer in southern California.