As noted in Table 18.1, the benefits of ionizing radiation have been known since 1905. In addition to its potential to reducetheincidenceoffoodbornediseases,food irradiation can be used to eliminate pests such as the screw worm fly, which preys on cattle, the Mediterranean fruit fly, and the tsetse fly, by the release of sterile insects. Worries about nuclear weapons, combinedwithanantiprogressideology, began to hinder food irradiation research afterthe war. Althoughthere wasatthat time an adequate supply of gamma rays, the high-energy, short-wavelength rays given off by radionuclides, the antitechnology factionconvincedtheCongressto control the development of nuclear technology for treating foods.
In 1958, when the Food, Drug, and Cosmetic Act was passed by the U.S. Congress, there were many unanswered questions. Would irradiated food be made radioactive? What would be the effect of this additional radioactivity above that of the background on human health? Would irradiation of food produce new toxic products such as carcinogens? Would the process produce products with excessive loss of nutrients or changes in food taste, odor, color, or texture? In the killing of pathogens, would new microbiological problems evolve? Also, what would be the adverse effects, if any, on the environment should there be accidents? What sources of radiation (gamma) and what doses would be suitable for irradiation?
Successful lobbying by well-known public figures in the movie and entertainment circles convinced the Congress to keep food irradiation under tight control, i.e., treating ionizing radiation as a "food additive." This part of the 1958 law, known as the Delaney Clause, assured that no irradiated food could be approved for consumption without a lengthy drawn-out procedure, thereby singling out and stigmatizing foods so treated by requiring a long period for research and petition writing to the FDA and the U.S. Department of Agriculture (USDA) and then many months or years for evaluation.
After 1961-1962, the U. S. Department of Army's food radiation research and development program made it the top priority to try to sort out the diverse claims, either pro or con, about irradiated foods. The U.S. Army Medical Services completed studies for testing in rats, mice, and beagle dogs, using 21 foods representing all major food classes in the diets of U.S. people. In June 1965 in a hearing by the Joint Committee on Atomic Energy, the army surgeon general submitted a statement that all foods irradiated at sterilizing doses up to 5.6 Mrad (56 kGy) using cobalt-60, or electrons at energies below 10 MeV, were wholesome, i.e., safe to eat and nutritionally adequate.
Nutritional assessments showed that the irradiation process was no more destructive to nutrients than other processes then being used commercially. It was also demonstrated that there were no toxic products formed in quantities that would be hazardous to the health and well-being of consumers.
The microbiological standard for irradiation-sterilized foods was to use a radiation dose sufficient to reduce a theoretical population of spores of Clostridium botulinum. This standard, recommended by the National Academy of Sciences and the National Research Council Advisory Committee to the army's program on food irradiation, was adopted. In the ensuing years, there was no record of any problem with possible C. botulinum survivors, although this has continued to be one of the antinuclear arguments against food irradiation.
Thousands of irradiated components of meals have been served to volunteers. In every respect, the tested irradiated foods have passed with soaring results. Irradiated foods have been eaten by astronauts on the moon flights and on many other space missions, by immunocompromised patients, and by military personnel in several parts of the world.
Every conceivable possibility for harm has been carefully considered — none has been found. Nor have any chemicals formed that are unique to food irradiation. In the meantime, irradiated foods have been approved by the health authorities in 40 countries.
Between 1964 and 1997, the World Health Organization (WHO), in concert with the Food and Agricultural Organization (FAO) and the International Atomic Energy Agency (IAEA), held a series of meetings of experts from many countries to assess the quality and safety of foods. In a meeting in September 1997, they recommended the approval of irradiated foods without restrictions at all doses, up to the highest dose compatible with organoleptic properties. At each meeting, the internationally recognized health authorities have concluded that all irradiated foods are safe to eat without the need for further toxicological testing, at doses as high as those allowing an acceptable taste.
In view of the foregoing, food scientists believe that the FDA and the USDA should follow the WHO/FAO/IAEA recommendation that food irradiation is a process. Scientists have thought for three decades that the legal fiction designating ionizing radiation as a food additive, instead of a food process, unjustly penalized food irradiation and helped delay its implementation for more than 30 years. On the other hand, during these years, the additive designation has stimulated those working in the field to perform at the highest level of good science, thus convincing the scientific community worldwide that food irradiation has an important role to play in combating hunger and disease.
In totality, scientists have reached their objective in documenting that food irradiation is a safe and beneficial process. Now scientists need to educate government officials, as well as health workers, food processors, marketers, and the public, on the safety and advantages of food irradiation.
With approximately 9000 people dying annually from food poisoning in the U.S., and an estimated 30,000,000 cases of food infection each year, there is little doubt that the time has come to use food irradiation more widely for the benefit of human health. Ironically, in applying ionizing radiation to protect public health against foodborne pathogenic bacteria, public health officers currently face the same arguments that were voiced against pasteurization at the beginning of the century and later against canned and frozen foods. In the history of pasteurization, many voiced disbeliefs of pasteurization's benefits for sanitation, nutrition, physical and bacteriological quality, consumer health and safety, and economics. Loss of hair, skin tone, and general well-being, as well as potency, was also claimed. These mistaken beliefs are cited currently against the irradiation of food.
Food irradiation is now recognized as another method of preserving food and ensuring its wholesomeness by sterilization or cold pasteurization, and has wide application worldwide. If it had been in place in the U.S., recent foodborne disease outbreaks caused by E. coli O157:H7, which are found in food-producing animals, would not have occurred. There have been tens of thousands of Salmonella, Campy-lobacter, Yersinia, Listeria, and Escherichia coli foodborne disease outbreaks related to poultry and meat, the totals exceeding millions of human illnesses, over the last 40 years since the Delaney Clause established the travesty that gamma rays were a food additive.
We may never know how many thousands of deaths and illnesses could have been prevented if public health authorities had implemented food irradiation and educated the public about its benefits. The morbidity and medical expense of meat-and poultryborne diseases can be prevented, just as milkborne disease can be prevented by pasteurization. All the bacteria cited previously can be present in unpas-teurized milk, even though the U.S. Public Health Service Grade A standards require that milk be free of disease-causing organisms. Imagine the public outcry if governments allowed the marketing of unpasteurized milk in which Salmonella or E.
coli virulent strains were found or soft cheese or Mexican-style cheese in which Listeria wasfound.
In 1984, Margaret Heckler, Secretary ofHealth,endorsedfoodirradiation,after lengthy studies had proven its safety. If public health officers had spoken out then for the irradiation of foods that are known to carry pathogenic bacteria, events such as the E. coli O157:H7 outbreaks from undercookedhamburger(3deathsandmore than 400 cases of illness) that occurred inthenorthwestU.S. inJanuary 1993 could have been prevented. Even today, no national or state local health authority speaks in favor of requiring pasteurization by irradiation of hamburger meat patties, of which some tens of millions are consumeddaily. Thesameattitudeandapathyexist in Europe, where Listeria-contaminated pork meat and other food caused the death of 63 persons in France, as reported in 1993. Since then, Listeria has become a serious public health problem in the U.S.
types of irradiation
What is irradiation? Irradiation is definedasexposuretoradiation(rays). Radius is taken from Latin, meaning ray. The radiationusedinthefoodirradiationprocess comes either from radioactive isotopes of cobalt or cesium or from devices that produce controlled amounts of x-rays, gammarays,orhigh-energyelectrons. The process exposes food to radiation but does not and cannot make the food radioactive. Gamma rays and x-rays emit waves of highfrequenciesandhighenergies.These waves produce enough energy to strip electrons from atoms, leaving ions (particles charged with electrical charge), or ionizingradiation.Ionizingradiationistheenergy that exists in the form of waves and is definedbyits wavelength. Asthe wavelength of energy gets shorter, the energy of the waveincreases. Theelectromagneticspectrum (Figure 18.1) identifies the kinds of energy that exist and how they are used. Visible light, radio and television waves, and microwaves are examples of nonionizing radiation. They cause molecules to move, but they cannot structurally change the atoms in the molecules. The energy is measured by frequency (Hz), which is the number of times per second that the wave completes its cycle in an electromagnetic field.
Simple cooking involves the absorption of infrared radiation or heat by the food. Early on, it was found that shortwave radiation could melt things such as a chocolate
Common name of wave
rf FM Radio Microwave
INFRARED < ULTRAVIOLET "HARD" X-RAYS
MICROWAVES E "SOFT" X-RAYS GAMMA RAYSr
106 107 108 109 1010 10" 1012 1013 1014 1015 1016 10" 1018 10IM 102 _I_I_I_I_I_I_I_I_I_I_I—
,12 HA13 HA14 m15 HA18 H A20
Energy of one photon _
(electron volts) 10-9 iQ-8 !Q-7 iQ-6 iQ-5 10-4 10-3 10-2 10-1 1 101 102 103 104 105 106
FIGURE 18.1 Electromagnetic spectrum.
The ALS X-Ray Elements
Frequency bar. Shortwave radiation led to the inventionofmicrowaves.In themicrowave,radio waves, with shorter wavelengths and higherfrequenciesthanthoseusedforcommu-nication, cause water and other polar molecules within food to vibrate. Vibration can be up to 2.5 billion times/sec, which is enoughvibrationtocauseheatbyfriction. Both cooking by heat and microwave are examplesoftheuseofnonionizingradiation.
High frequencies constitute ionizing radiation. Theradiationpassesthroughthe food without generating intense heat, disruptingcellularprocessessuchassprouting, ripening, or growth of microbes, parasites,andinsects.Ionizingradiationhashigh energy — high enough to change atoms by knocking an electron from them to form an ion, but not high enough to split atomsandcause exposedobjectstobecome radioactive. Therefore, the sources of radiationallowedforfoodprocessing(cobalt-60, cesium-137, accelerated electrons, and x-rays) cannot make food radioactive. Food irradiation makes use of high frequenciesconstitutingionizingradiation.In contrast, during a nuclear meltdown, incrediblyhighlevelsof ionizingradiationare emitted, because of which not only is the growth of microorganisms disrupted but the food itself can become radioactive. Thus,thedifferenceis amatterofmagnitude, owing to which people can enjoy the benefitsofionizingradiationwithno worries about radioactive contamination.
Foods are processed in facilities designedforthatpurpose. Figure 18.2 shows the floor plan for a gamma irradiation facility. It consists of three areas. The outer area where food is received for processing and stored before and after processing is like any other food warehouse. If frozen or perishable foods are processed in the facility, it must have appropriate refrigeration facilities. No other requirements are unique to the area. The second area is the conveyor or other system used to transport the food to be processed. Food to be processed is loaded onto the conveyor and carried to the irradiation source, where it absorbs the energy needed to accomplish the desired effect. The third, the inner area, is the processing room. In this room, the source is stored until needed to process the food. In the case of gamma sources, a pool of water is used to store the source when it is not used to prevent radiation from escaping. When the source is raised into the room, concrete walls provide a shield to prevent the escape of radiation into the storage area. In the case of irradiation generated by a machine, the same shielding is used to prevent escape of radiation, but no other shielding is needed because no radiation is generated when the machine is turned off.
Processing facilities are safe for the employees who work there and for the surrounding environment. Facilities using gamma sources must be licensed by the U.S. Nuclear Regulatory Commission or an equivalent state agency to assure that they can be operated safely. All facilities must meet requirements of the Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA) to assure that workers and the environment will not be adversely affected in any way. In addition, when gamma sources are moved to or from the facilities, they are carried in special containers that have been proven safe for the purpose by the U.S. Department of Transportation. In more than four decades of transporting gamma sources in North America, there has never been an accident that has resulted in the escape of radioactive materials into the environment. Also, no radioactive waste is generated by irradiation; all spent sources are returned to the firm that supplied them for storage or further processing.
During the process of food irradiation, ions are formed. The ions can cause chemical changes within the food, e.g., splitting of water molecules, which may recombine to form hydrogen peroxide. Such products may react with food to lower nutritional value or produce undesirable by-products. Food irradiation is a cold process, i.e., it achieves its effect with little rise in the temperature of the food. There is little, if any, change in the physical appearance of irradiated foods, because they do not undergo the changes in texture or color as do foods preserved by heat pasteurization, canning, or freezing. Food remains close to its original state. However, problems that have occurred include some off-flavors in meat and excess tissue-softening, which has been documented in fresh peaches and nectarines.
effectiveness of irradiation
Currently, there are three dose levels of food irradiation, based on their applications. Low-dose applications, using less than 0.1 kGy, are effective against sprouting of infesting insects. Doses of 0.2 to 1 kGy kill infesting insects. Low-dose irradiation delays ripening and extends the shelf life of fruits, e.g., strawberries, bananas, mangoes, papayas, guavas, cherries, tomatoes, and avocados. Pasteurizing doses
(radurized) of 1 to 3 kGy kill populations of microbes, and are effective against Salmonella, Campylobacteria, and parasitic liver flukes. Such doses destroy pathogenic microorganisms that might be present in milk and delay spoilage by significantly reducing the number of microbes responsible for spoilage. In Europe, irradiated milk has been used for years and is very popular because before opening it can be stored safely at room temperature. Sterilizing doses (reappertization) of 25 to 50 kGy decrease the number of nonsporing pathogenic organisms.
Early trails of irradiated foods resulted in undesirable changes both in taste and texture. Dairy products (cheeses) proved not to be good candidates for irradiation. There were also changes in aroma and texture of citrus crops.
Currently, the FAO and WHO allow only forms of ionizing energy for food irradiation that are unable to cause the food to become radioactive, i.e., x-rays and cobalt-60 or cesium-137 to produce gamma rays. Cobalt-60 and x-rays have been used many years in medical devices. Cesium-137 is a by-product of the nuclear industry and has become less popular. Each has its advantages and disadvantages. The 5-mEV x-ray machines offer the advantage of producing radiation only when desired. However, such machines are more complex technically and the electron beams are limited because they do not penetrate very far into the food. Cobalt-60 isotopes are problematic because they continuously emit radiation and cannot be turned off. The lives of the isotopes are limited and subject to regulatory controls. A typical facility using cobalt-60 has the isotopes doubly encapsulated in 18-in. stainless steel tubes. Food passes through the radiation on conveyor belts for exposure.
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