Food is a necessity of human life, providing energy for the development, growth, and maintenance of the body. Yet, the consumption of food can also be the cause of illness and disease from pathogenic microorganisms. Heat treatments, such as cooking or pasteurization, have been the primary methods which food has been rendered safe to eat. However, changes in dietary habits, food supply chains, and new preparation techniques that do not include thermal processing have increased the risk that pathogens may be ingested. Changes in population demographics that include more individuals with compromised immune systems (such as the elderly) place greater concern on the safety and wholesomeness of the food consumed. The emergence of new pathogens in foods, such as the presence of Escherichia coli 0157:H7 in ground beef, poses additional challenges on current food safety technologies. Food safety systems must evolve to meet these challenges with the development of new technologies. One food safety technology that is currently available but significantly underutilized is food irradiation. Food irradiation has a long and studied history that demonstrates its safety, effectiveness, and applicability to some of today’s food safety challenges.
Importance of Food Safety
The United States is often referred to as having one of the safest food supplies in the world, but illness from food borne illness pathogens are still common. In the United States, over 76 million persons are estimated to contract a food borne illness annually, 325,000 are hospitalized due to their illness, and there are approximately 5200 deaths as a direct result of food borne illness (Mead et al, 1999). While most acute food borne illness is caused by viruses (67%), pathogenic bacteria account for nearly 75% of all hospitalizations and deaths (only 7% due to virus). Only four bacterial pathogens and one parasite are responsible for more than 90% of food-related hospitalizations and deaths: salmonella, listeria, campylobacter, Escherichia coli 0157:H7, and Toxoplasma. Children are particularly susceptible to complications from bacterial food borne illness due to still developing immune systems and lower body weight (Buzby, 2001). In addition, the economic costs of food borne illness are high. The Economic Research Service (ERS) estimates the cost to the U.S. economy of food borne illness caused by the above five pathogens to be $7 billion in medical costs, lost productivity, and premature death annually (Buzby, Roberts, Lin, & MacDonald, 1996). This estimate may be conservative as not all factors and complications related to food borne illness, such as chronic health issues, are considered in the analysis.
Food borne illnesses are preventable public health diseases. Preliminary data for 2008 projects that the number of food borne illnesses has remained relatively constant over the last several years (Centers for Disease Control and Prevention (CDC), 2009). The lack of progress in reducing the incidence of food borne illness indicates the need for the implementation of new techniques and processes to fill existing gaps in the food safety system. The use of irradiation is one such solution that has been demonstrated to enhance the safety of food by reducing potential pathogens (Tauxe, 2001). As part of a comprehensive food safety program, irradiation should be considered as a supplemental tool to help control food pathogens and reduce the risk of food borne illness.
Food Irradiation Technology
Food irradiation is the process of exposing pre- or post-packaged foods to a source of ionizing radiation for a specific time under controlled conditions in specially designed chambers (International Consultative Group on Food Irradiation (ICGFI), 1999). Three types of ionizing energy are used in food irradiation: gamma rays, X-rays, or electron beams. With very short wavelengths similar to ultraviolet light and microwaves, gamma rays do not generate neutrons (the subatomic particles that make substances radioactive) so food and packaging that have been irradiated are not radioactive (Environmental Protection Agency (EPA), 2009). Only low-level radioisotopes cesium-137 and cobalt-60 are approved as sources of gamma radiation for food. X-rays and electron beams are machine generated using electricity that is powered on and off as needed. All three energy sources have the ability to kill or inactivate pathogens and spoilage organisms without initiating detrimental changes to the food product. Irradiation does not cook food like a microwave, reverse the effects of spoilage that has already occurred, or remove other contaminants from the food (Loaharanu, 2003).
Irradiation inactivates or kills pathogens and spoilage organisms by causing damage to their DNA that makes the organism unable to grow or reproduce (Tauxe, 2001). The time that food is exposed to one of the three ionizing energy sources depends on the type of organism, type of food, its density, if packaging is present, and the energy source itself. Electron beam is a very rapid and efficient irradiation process that requires only a few seconds of exposure to kill pathogens depending on product density (Lewis, Velasquez, Cuppett, & McKee, 2002). Gamma and X-rays are less efficient at penetrating food matrices, taking considerably longer to achieve the same kill level. Regardless of the technique used, the food is never in direct contact with the source of the energy. The ionizing energy waves generated penetrate into the food but do not stay in the food or cause it to become radioactive (Thayer, Josephson, Brynjolfsson, & Giddings, 1996). The ionizing energy levels needed to destroy pathogens is very low and is measured in kiloGrays (k-Gy). On average, only 1-10 k-Gy is required to make food products safe from food borne pathogens and spoilage organisms. At this level of exposure, there is no significant increase in temperature or change in composition of the food being treated (ICGFI, 1999).
Research and Regulatory
The use of irradiation to improve the safety and shelf-life of food has a long history. Initial studies of irradiating food date to the late 1800s with the first patents on the use of irradiation to preserve food issued in 1905 (Parnes et al., 2003). The study of food irradiation was accelerated during World War II when the Department of the Army sponsored research for using irradiation to preserve fruits, vegetables, dairy products, fish and meats. After World War II, the National Food Irradiation Program was initiated to continue research on the use of irradiation for foods. In 1963, the Food and Drug Administration (FDA) approved the first use of food irradiation as a treatment to disinfest insects from wheat and wheat powder (CDC, 2005). The use of irradiation on several other food product groups has been approved over the years (see Figure 1), including dry spices, fresh pork, fruits, poultry, red meat products, and leafy greens. The National Aeronautics and Space Administration (NASA) in 1972 initiated the use of irradiation to sterilize food for astronauts (Tauxe, 2001).
Figure 1 – FDA Approval for use of Food Irradiation (CDC, 2005 )
Product Purpose Date of Rule
Wheat and Wheat powder Disinfest insects 1963
White potatoes Preservation 1965
Dry spices and seasonings Decontamination/disinfest 1983
Pork and fresh non-cut processed cuts Eliminate Trichinella spiralis 1985
Fresh fruits Delay Ripening 1986
Dry enzyme preparations Decontamination 1986
Poultry Pathogen reduction 1990
Red meat Pathogen reduction 1997
Fresh shell eggs Salmonella reduction 2000
Fresh Lettuce and Spinach Pathogen reduction 2008
The scientific study of food irradiation has been ongoing for over 70 years. Nearly 40 years of research preceded the first approval of its use on food for human consumption. The accumulation of scientific study and testing on this technology prior to obtaining its first approval for use is one of the longest for a food technology (Wood & Bruhn, 2000). All aspects of the use of irradiation for food have been studied for both general effects (i.e. environmental, safety, public health) and specific effects (i.e. toxicological, microbial, wholesomeness, organoleptic) on the foods being irradiated. The comprehensiveness of this research has defined the parameters of efficacy, safety, and application of this food processing technology. Overall, the research on irradiation has shown it to be an effective, efficient, and safe procedure to reduce pathogens and spoilage organisms in food.
These attributes has been recognized by many governmental, regulatory, and international agencies that have endorsed the use of food irradiation as an adjunct to existing food safety systems. Food irradiation is currently approved in over 50 countries, with 33 using the technology commercially on about 50 different food products (ICGFI, 1999). The World Health Organization (WHO) and Food and Agriculture Organization (FAO) encourage the use of food irradiation as an additional process tool to help improve the safety and preservation of foods (International Consultative Group on Food Irradiation, 1999). Overall, more than 100 international and professional organizations have endorse the use of food irradiation, including the American Medical Association, Institute of Food Technologists, American Dietetic Association, Health Physics Association, and the Scientific Committee of the European Union (Center for Infectious Disease and Policy, 2006).
Benefits of Food Irradiation
The primary benefit of food irradiation is that of improving public health by reducing food borne illness through the elimination of pathogenic organisms in a food product, rendering it safe for human consumption. Research studies have demonstrated that irradiation reduces, inactivates, or destroys the pathogenic microorganisms that cause most food borne illnesses, including salmonella, Escherichia coli 0157:H7, listeria, and campylobacter (Shea, 2000). The Centers for Disease Control and Prevention estimate that if just 50% of the poultry and meat consumed in the United States was irradiated there would be 900,000 fewer food borne illnesses and over 350 fewer deaths annually (Tauxe, 2001).
Food irradiation also provides additional environmental and economic benefits. The use of chemical fumigants and heat treatments are significantly reduced when irradiation is used on dry products (i.e. spices, seasonings, grains, flours) and fresh produce to inactive microorganisms and insects (Thayer & Rajkowski, 1999). Economically, irradiation of fresh produce and root vegetables can extend shelf-life by delaying product ripening and inhibiting sprouting without changing the flavor, aroma, texture, or color of the products. Irradiation can also be used to sterilize foods (i.e. use by NASA for space program, meals for immunocompromised individuals). If appropriately packaged, sterilized foods can be kept for years without refrigeration, similarly to canned foods (Parnes et al, 2003).
Limitations of Food Irradiation
Irradiation is not an applicable treatment for all foods. Some types of food may develop off-odors (i.e. high fat meats, poultry), undergo color, texture, or flavor changes (i.e. grapefruit), or have reduced shelf-life when irradiated (i.e. oysters) (Tauxe, 2001). Milk and other dairy products are also more susceptible to detrimental quality changes when irradiated.
Basic food safety practices are not supplanted or superceded by irradiation. Certain food borne hazards are resistant or not effectively controlled using irradiation. Inactivation of viruses and bacterial spores requires significantly higher doses of ionizing energy than is allowed by regulation or practical for food quality (Osterholm & Norgan, 2004). Similarly, toxins and prions are not eliminated from food by irradiation. Good food safety systems, processes, and practices are necessary to prevent these hazards from entering the food supply.
The Debate over Food Irradiation
Support for the use of irradiation on food is not universal. Consumer, industry, and advocacy organizations have publicly opposed the use of irradiation on food for a variety of reasons. While there is diversity in the debate on food irradiation, four primary arguments have emerged:
(1) Phytosanitation and Pathogen Elimination
There is concern that the use of irradiation will foster complacency in the food supply chain and lead to substandard food safety practices. This will allow additional contamination to enter the food supply increasing the risk of food borne illness from hazards not controllable with irradiation (Jenkins & Worth, 2006). While this concern has some validity, substandard food safety practices are currently present in the food supply chain. The recent salmonella outbreak from peanut products illustrates the potential for abuse of current practices (Food and Drug Administration, 2009). Irradiation is another tool in the food safety process that provides an additional barrier to biological contamination. As with other food processes, such as retorting for canned products or pasteurization of milk, irradiation is not a substitute for good food safety practices and adherence to good manufacturing processes (Stewart, 2004). However, good food safety practices will not eliminate all risk of contamination. The production of ground beef is an example where even with good food handling practices, E. coli 0157:H7 is still found in a small percentage of the final product (Osterholm & Nogan, 2004). Irradiation would ensure that even this small level of high risk contamination does not reach the consumer.
A second concern is that viruses (i.e. norovirus) are responsible for nearly 70% of all food borne illness (Mead et al, 1999), yet are not eliminated by this intervention. Irradiation at currently approved levels does not inactivate viruses or prions (CDC, 2005). As mentioned previously, irradiation is an additional tool to help reduce risk and enhance food safety. Good hygiene and food safety practices are the foundation of producing food that is safe and free of contamination. It should also be noted that irradiation does not prevent contamination from food handlers or consumers during preparation. Safe food handling practices must be adhered to all through the food supply chain.
A third concern in this area is that not all microorganisms are destroyed in food due to allowable irradiation levels, exposure time, and variation in food matrix and density. The remaining microorganisms may become radiation-resistant and develop into super strains of hard-to-kill pathogens. There is a theoretical possibility of mutation from the use of irradiation, however the probability of unique mutations due to irradiation are minimal (Shea, 2000). Studies have not found significant alteration or mutation of microorganisms that increase virulence, resistance, or survival attributed to irradiated food. The World Health Organization (WHO), the Food and Agricultural Organization (FAO), and the U.S. Food and Drug Administration (FDA) have all concluded that there is little risk of microbial mutation due to food irradiation (WHO, 1994; Morehouse, 1998).
(2) Chemical Alteration of Food
The irradiation of food generates unique radiolytic byproducts, 2-alkylcyclobutanones that are carcinogenic and mutagenic in animals, and potentially harmful to individuals (Osterholm & Nogan, 2004). The introduction of any energy source to food generates changes in the food matrix. Cooking, microwaving, or grilling of food produces byproducts that are similar to irradiation but only in much greater amounts (Shea, 2004). Animal feeding studies with irradiated food have been conducted for over 60 years resulting in no significant adverse results. The health concerns over radiolytic compounds stems from a 2002 European study (Osterholm & Nogan, 2004; Shea, 2004). Rats were fed with high levels of synthetically produced radiolytic compounds which promoted tumor growth when the rats were exposed to known carcinogens. However, the researchers cautioned that extrapolation of these results to humans that consume raw irradiated food was not appropriate. Further review by the European Commission Scientific Committee on Food concurred with the researchers’ conclusions. Other reviews by the FDA, WHO, FAO, and the International Atomic Energy Agency have deemed that the formation of compounds in irradiated food is essentially the same as those formed during thermal processing (i.e. cooking) and do not pose any health hazards to humans (Stewart, 2004).
(3) Nutritional Quality
There are concerns that irradiation causes a breakdown of nutrients in food, particularly vitamins. While the decrease in nutritional content is similar to what occurs in cooking, consumers are not made aware or educated on how to compensate for the decrease in nutrition, especially for ready-to-eat food such as fruits and vegetables. The lack awareness will cause deficiencies in the diet that can affect the health of individuals consuming irradiated foods. There is a slight loss of nutritional value in foods that have been irradiated (Smith & Pillai, 2004). However, the nutritional loss is less than that from other conventional food processing procedures such as canning, pasteurization, or drying and significantly less than the loss that occurs through cooking or microwaving. Carbohydrates and proteins are minimally affected by irradiation but fats can oxidize affecting the aesthetics of irradiated food (color, odor, and taste) but not its nutritional value.
Vitamins are more susceptible to irradiation with four (B1, C, A, E) being particularly sensitive (ICGFI, 1999). However, the loss of these vitamins due to irradiation is similar to thermal food processes, such as pasteurization or cooking. Additionally, vitamin loss is minimized when food is irradiated in an oxygen-free environment or in a cold or frozen state (Thayer, Josephson, Brynjolfsson, & Giddings, 1996). Most food irradiated processes use one or a combination of these techniques to minimize loss of nutrients. The FDA has determined that the nutritional loss due to irradiation is not significant enough to have a detrimental effect on the nutrient intake of individuals that consume irradiated foods (Morehouse, 1998). The same conclusions have been note by the World Health Organization, the United Nations Food and Agriculture Organization, American Dietetic Association, the American Medical Association, and many other governmental and public health organizations (CIDRAP, 2006).
(4) Environmental Impact
Any process that includes the use of nuclear material surfaces concerns about safety and security. There is wariness among the public over the potential of nuclear accidents (either unintentional or intentional) that may have significant consequences for health and the environment (Jenkins & Worth, 2006). The use of irradiation will generate additional nuclear waste that will require storage and/or treatment at nuclear waste facilities that are already overburdened. This concern is multiplied when the number of irradiation facilities required to handle the volume of food products is factored into the calculation.
The irradiation process used for food is essentially the same as the process that has been used to sterilize medical equipment and healthcare supplies for over 40 years (Shea, 2000). There are approximately 170 facilities globally that currently utilize gamma rays, generated primarily from cobalt-60, to sterilize medical materials. There have been no significant incidents or problems with these facilities or handling of radioisotopes from these facilities. The primary radioisotope used in the irradiation process, cobalt-60, is classified as a low-level radiation source manufactured specifically for medical and food applications (EPA, 2009). It has a very short half-life of 5.3 years (i.e. half of its radiation is lost in 5 years) that decays to non-radioactive nickel. Spend cobalt-60 rods are returned to the supplier for renewal or storage as low-level radioactive waste until it can be recycled. Since cobalt-60 does not produce neutrons it can not make other materials radioactive that prevents the possibility of a nuclear chain reaction, meltdown, or explosion (ibid; ICGFI, 1999). Facilities in the United States that utilize radioisotopes are regulated by the U.S. Nuclear Regulatory Commission that impose specific requirements on the operation of the facility, and the handling, storage, and disposal of the radioactive source (Smith & Pillai, 2004). Worker safety is regulated and monitored by the Occupational and Health Administration. Facilities are inspected regularly to ensure compliance with regulations and safety measures. The other two types of irradiation, electron beam and X-rays, do not use radioisotopes as a source of energy. Both of these technologies utilize electricity to generate ionizing energy. These facilities are classified under the same regulatory categories as medical, dental, and industrial devices using similar technologies, which falls under the regulatory authority of the FDA and state regulatory agencies (ibid). These facilities are also routinely inspected to ensure compliance with regulations and licensing requirements.
A significant global portfolio of research has been developed over the last 60 years on food irradiation. This body of evidence has clearly established the safety and effectiveness of irradiation. In a 2000 report to Congress, the General Accounting Office (GAO, 2000) concluded that:
“Scientific studies conducted by public and private researchers worldwide over the past fifty years support the benefits of food irradiation while indicating minimal potential risks. These studies have not borne out concerns about the safety of consuming irradiated food… [such as] the loss of nutrients [or] the presence of toxic substances resulting from irradiation. [Nor] is there evidence or reason to expect that irradiation produces more virulent pathogens among those that survive irradiation treatment.”
Concerns expressed that irradiated food is less safe, lower in nutrients, and poorer quality are not supported by the vast amount of research that has been done demonstrating the safety, wholesomeness, and quality of irradiated food. The USFDA, USDA, and organizations worldwide such as the World Health Organization, Food and Agriculture Organization, the European Food Standards Agency have agreed that the science of food irradiation is sound (CDC, 2005). These organizations along with governmental agencies, professional organizations, and public health professionals endorse the use irradiation as an additional process tool to enhance food safety.
Irradiation facilities have been in use around the world for over 50 years with excellent safety records for both the facility and the individuals that work in them. Regulations have been developed and improved over the years to protect workers, the public, and the environment. The introduction of non-radioactive irradiation technologies provides alternatives that further minimize the risks of these facilities.
The use of food irradiation is an underutilized process for food safety that can further help decrease the burden of food borne illness. Irradiation is not a substitute for good food safety practices, a magic bullet to eliminate all food borne hazards, or applicable to all foods. However, it is an important complementary technology that should be utilized more extensively as part of a food protection program on those foods for which it has be approved.
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