Irradiation as a Food Safety and Preservation Technique

Food Irradiation

Radiation is broadly defined as energy moving through space in invisible waves, whereas radiant energy has differing wavelengths and degrees of power. Thus, Light, infrared heat, and microwaves are forms of radiant energy, where these waves that bring radio and television broadcasts into your homes. Nonetheless, boiling and toasting use low-level radiant energy to cook food. The radiation of interest in food preservation is ionizing radiation, also known as irradiation. These shorter wavelengths are capable of damaging microorganisms such as those that contaminate food or cause food spoilage and deterioration. That capability, plus the fact that much of our food supply is lost due to spoilage and insects each year is why scientists have been experimenting with irradiation as a method of food preservation since 1950. They have found irradiation to be a controlled and very predictable process.

Food irradiation is a processing technique that exposes food to electron beams, X-rays or gamma rays, where process produces a similar effect to pasteurization, cooking or other forms of heat treatment, refrigeration, freezing or treated with chemicals to destroy insects, fungi or bacterial that cause food to spoil or cause human disease and to make it possible to keep food longer and in better conditions, but with less effect on appearance and texture. The major purpose of food irradiation is to reduce or eliminate harmful pathogens like E. coli or salmonella that can be present on food products such as spices and ground beef. Irradiation can also reduce the microorganisms that cause food to spoil and inhibit processes like sprouting in potatoes and onions, thereby extending shelf life. Another use for irradiation is to kill insect pests found in food that has been imported from other countries.

Technology

Irradiation is a process whereby products are exposed to a source of radiation in order to achieve a specific effect. For food irradiation, the source of irradiation could be gamma from a Cobalt-60 irradiator, electron beams or x-rays. Food absorbs energy when it is exposed to ionizing radiation, where amount of energy absorbed is called 'absorbed dose', which is measured in units called grays (Gy) or kilograys (kGy), where 1kGy = 1,000Gy. The energy absorbed by the food causes the formation of short-lived molecules known as free radicals, which kill bacteria that cause food poisoning. The products are exposed to radiation for a prescribed amount of time that will reduce the number of microorganisms on the food to a safe level. However, irradiation does produce chemical changes in foods, which called free radicals or "radio-lytic products", may sound mysterious, but they are not, because they have been scrutinized by scientists in making safety assessments of irradiated foods. Nonetheless, any kind of treatment causes chemical changes in food. For instance, heat treatment, or cooking, produces chemicals that could be called "thermolytic products". Scientists find the changes in food created by irradiation minor to those created by cooking, because products created by cooking are so significant that consumers can smell and taste them, whereas only a chemist with extremely sensitive lab equipment may be able to detect radiolytic products.

In irradiation, the process involves exposing the food, either packaged or in bulk, to carefully controlled amounts of ionizing radiation for a specific time to achieve certain desirable objectives. When microbes present in the food are irradiated, the energy from the radiation breaks the bonds in the DNA molecules, causing defects in the genetic instructions. Unless this damage can be repaired, the organism will die or will be unable to reproduce, which matters if the food is frozen or fresh, because it takes larger radiation dose to kill microbes in frozen foods. Thus, effectiveness of the process depends also on the organism’s sensitivity to irradiation, on the rate at which it can repair damaged DNA, and especially on the amount of DNA in the target organism such as parasites and insect pests, which have large amounts of DNA, are rapidly killed by an extremely low dose of irradiation. But it takes more irradiation to kill bacteria, because they have less DNA and viruses are the smallest pathogens that have nucleic acid, and they are, in general, resistant to irradiation at doses approved for foods. If the food still has living cells, they will be damaged or killed just as microbes are, which is a useful effect that can be used to prolong the shelf life of fruits and vegetables because it inhibits sprouting and delays ripening. 

Irradiation, at the levels normally used in food processing, destroys most, but not necessarily every single microorganism present which does not sterilize the food.  Nevertheless, consumers must take appropriate precautions, such as refrigeration and proper handling and cooking, to make sure that potentially harmful organisms do not present a problem. After treatment, the surviving disease-causing and food spoilage organisms may start to multiply again if the food is not properly handled. The disease-causing organisms in irradiated food are just as dangerous, but not more so, as the same organisms in non-irradiated food. One concern has been that irradiation does not kill the bacteria that causes botulism. However, studies also have shown that in both irradiated and non-irradiated food, spoilage organisms will grow and alert consumers to spoilage before botulism-causing bacteria can produce toxin.

All known methods of food processing and even storing food at room temperature for a few hours after harvesting can lower the content of some nutrients, such as vitamins. At low doses of radiation, nutrient losses are either not measurable or, if they can be measured, are not significant. At the higher doses used to extend shelf-life or control harmful bacteria, nutritional losses are less than or about the same as cooking and freezing. Foods treated by irradiation generally are as nutritious as or better than the same food treated by conventional methods such as cooking, drying and freezing. The effects of irradiation at doses required for microbial control in food are often compared to a milder form of the changes that occur during cooking. For spices where a microbial control step may be a requirement, irradiation provides less of a negative impact than some alternatives such as fumigation or elevated temperature processes. Irradiation; therefore, can result in a higher quality product. At doses used for phytosanitary irradiation, and even lower doses for sprout inhibition in potatoes and onions, irradiation has been shown to improve the shelf life with little to no negative impact to taste or quality.

Consumer Safety

As the food passes through the irradiation field, energy passes through the food. The energy will destroy bacteria that cause disease; however, it will not affect the quality of the food. The energy of the irradiation cannot make the food radioactive. The food never comes into contact with any radioactive materials. Decades of research worldwide, have shown that irradiation of food is a safe and effective way to kill bacteria in foods and extend its shelf life, where food irradiation has been examined thoroughly by joint committees of the World Health Organization (WHO), the United Nations Food and Agriculture Organization (FAO), by the European Community Scientific Committee for Food, the United States Food and Drug Administration and by a House of Lords committee. In 2011, the European Food Safety Authority reviewed the evidence and reasserted the opinion that food irradiation is safe.

Certain countries have approved the irradiation of spices, dried seasoning, potatoes, wheat, flour, onions, and fresh or frozen ground beef. The most commonly irradiated foods are spices. Food irradiation is an option available to producers to improve the safety of their food products, or otherwise improve quality or shelf life.

Packaging

If the purpose of irradiation is to eliminate pathogens in food, then packaging must be in place that ensures that food can’t get re-contaminated. Also, the packaging material should be approved based on studies that show that when it is irradiated, it does not form any harmful byproducts that can get into or on the food.

Pre-packaged foods that have been wholly irradiated must display the international radiation symbol, along with a statement that the product has been irradiated. Food that is not pre-packaged must have a sign with this information displayed beside the food.

Pre-packaged foods that contain an irradiated ingredient which is 10 per cent or more of the finished product must be identified in the list of ingredients as "irradiated". If the ingredient makes up less than 10 per cent of the finished product, it is exempt from the labelling requirements.

Food irradiation does not guarantee zero risk, but it greatly reduces bacteria and other microorganisms that may be present in food. Irradiation is an optional tool that can be used by the food industry on certain foods to enhance the safety of their products.

Irradiated food must still be handled, stored and cooked properly like all other foods. The rules of safe food handling, which include proper sanitation, packaging, storage and preparation, still need to be followed.

Irradiation cannot restore the palatability of food that is already spoiled. If food looks, smells or tastes bad before irradiation, it will still look, smell and taste bad after irradiation.

Food that has been irradiated in Canada, the United States and most other jurisdictions, must display a symbol called the Radura accompanied by explanatory wording such as “Treated by Irradiation.”

Since many bulk spices used in the restaurant and food packaging industry are irradiated and are only added in small quantities to prepared foods, it is not required to label the prepared foods or foods served in restaurants with the symbol.

Potential Consequences of Irradiated Food

Irradiation damages food by breaking up molecules and creating free radicals, where free radicals kill some bacteria, but they also bounce around in the food, damage vitamins and enzymes, and combine with existing chemicals (like pesticides) in the food to form new chemicals, called unique radiolytic products (URPs). 

Some of these URPs are known toxins (benzene, formaldehyde, lipid peroxides) and some are unique to irradiated foods, where scientists have not studied the long-term effect of these new chemicals in our diet, which we cannot assume they are safe. 

Irradiated foods can lose 5%-80% of many vitamins (A, C, E, K and B complex), where the amount of loss depends on the dose of irradiation and the length of storage time. 

Most of the food in the American diet is already approved by the U.S. Food and Drug Administration (FDA) for irradiation: beef, pork, lamb, poultry, wheat, wheat flour, vegetables, fruits, shell eggs, seeds for sprouting, spices, herb teas (Dairy is already pasteurized).

Irradiation damages the natural digestive enzymes found in raw foods, which means the body should work harder to digest them. 

If unlabeled, raw foods that have been irradiated look like fresh foods, but nutritionally they are like cooked foods, with decreased vitamins and enzymes.

Irradiated fats tend to become rancid. 

When high-energy electron beams are used, trace amounts of radioactivity may be created in the food.

The longest human feeding study conducted was 15 weeks as to bit older data, where no one knows the long-term effects of a life-long diet that includes foods which will be frequently irradiated, such as meat, chicken, vegetables, fruits, salads, sprouts and juices. 

There are no studies on the effects of feeding babies or children diets containing irradiated foods, except a very small and controversial study from India that showed health effects. 

Studies on animals fed with irradiated foods have shown increased tumors, reproductive failures and kidney damage which were not clearly distinguished the root causes, however, some possible causes are: irradiation-induced vitamin deficiencies, the inactivity of enzymes in the food, DNA damage, and toxic radiolytic products in the food.