Irradiation of Food
Food irradiation is a technology that uses radiation to control food spoilage by destroying food borne pathogens. Since the results are similar to pasteurisation it is also called “cold pasteurization.” The difference is that pasteurization uses heat to kill microorganisms, bacteria and viruses that may be present in the food whereas irradiation uses ionizing radiation. The application is used to inhibit sprouting, delay ripening, and improve re-hydration.
Ionizing radiation damages DNA so that
- microorganisms stop growing and can no longer continue their pathogenic activities
- spoilage-causing micro-organisms cannot continue their activities
- insects do not survive, or become incapable of proliferation
- plant ripening or ageing process is delayed
How is food irradiated?
When bulk or packaged food passes through an irradiation chamber on a conveyor belt food is irradiated. The food does not come into contact with the radioactive material but passes through a radiation beam much like torchlight. The amount of irradiation depends on the type of food and the specific purpose for which irradiation is being used. The conveyor belt is important as the speed of the belt controls the exposure time to the food. The actual delivered dose is measured by dosimeters within the food containers. Cobalt-60 is the most commonly used radionuclide for food irradiation. However, there are also large cesium-137 irradiators and the army has also used spent fuel rods for irradiation.
Effects of ionizing radiation on food
- Causes disruption of internal metabolism of cells
- Causes DNA cleavage (also called spitting of DNA strands)
- Formation of free radicals
- Disrupts chemical bonds
Sources of Irradiation
- Electron irradiation beam uses electrons, accelerated in an electric field, to a velocity that is close to the speed of light. Electrons are particulate radiation and have cross section many times larger than photons. Electron beams do not penetrate the product beyond a few inches, depending on product density.
- Gamma radiation is radiation of photons in the gamma part of the electromagnetic spectrum. The radiation is obtained through the use of radioisotopes, generally Cobalt-60. Food irradiation using Cobalt-60 is the preferred method by most processors, because the deeper penetration enables administering treatment to entire industrial pallets or totes, reducing the need for material handling.
The irradiation process has a wide range of uses and works with both large and small quantities of food. For example,
- a single serving of poultry can be irradiated for use on a space flight
- or a large quantity of potatoes can be treated to reduce sprouting during warehouse storage
Irradiation is most useful in four areas
Irradiation can destroy or inactivate organisms that cause spoilage and decomposition so self life increases. Irradiation is an energy efficient food preservation method and has more advantages than traditional canning. Irradiated products resemble fresh state closely as the texture, flavor, and color are almost the same. Using irradiation to preserve foods does not require any additional liquid, nor does it cause the loss of natural juices. Food can be irradiated after being packaged or frozen.
Sterilization Foods that are sterilized by irradiation can be stored for years without refrigeration just like canned (heat sterilized) foods. With irradiation it is possible to develop new shelf-stable products. It is cold sterilization.
Control sprouting, ripening, and insect damage: Irradiation offers an alternative to chemicals for use with potatoes, tropical and citrus fruits, grains, spices, and seasonings. However, since no residue is left in the food, irradiation does not protect against re -infestation unlike insect sprays and fumigants.
Control of food pathogens Irradiation can be used to effectively eliminate those pathogens that cause foodborne illness, such as Salmonella.
On the basis of the dose of radiation the application is generally divided into three main categories as detailed under. (The dose of radiation is measured in the SI unit known as Gray (Gy). One Gray (Gy) dose of radiation is equal to 1 joule of energy absorbed per kg of food material. In radiation processing of foods, the doses are generally measured in kGy (1,000 Gy)
Low Dose Applications (up to 1 kGy) for
- Sprout inhibition in bulbs and tubers 0.03-0.15 kGy
- Delay in fruit ripening 0.25-0.75 kGy
- Insect disinfestations including quarantine treatment and elimination of food borne parasites 0.07-1.00 kGy
Medium Dose Applications (1 kGy to 10 kGy) for
- Reduction of spoilage microbes to prolong shelf-life of meat, poultry and sea foods under refrigeration 1.50–3.00 kGy
- Reduction of pathogenic microbes in fresh and frozen meat, poultry and sea foods 3.00–7.00 kGy
- Reducing the number of microorganisms in spices to improve hygienic quality 10.00 kGy
High Dose Applications (above 10 kGy) for
- Sterilisation of packaged meat, poultry and their products which are shelf stable without refrigeration. 25.00-70.00 kGy
- Sterilisation of hospital diets 25.00-70.00 kGy
- Product improvement as increased juice yield or improved re-hydration
Advantages of Food Irradiation
- There is little or no heating of food
- Packaged or frozen foods can also be treated
- No chemicals are used for preservation of fresh foods
- Low energy requirements
- There is no comparable change in nutritional value
- High automation
Disadvantages of Food Irradiation
- High capital costs
- Possible development of resistant MO
- Inadequate analytical procedures to detect irradiation in food
- Public resistance
U.S.A. has approved irradiation for packaging material, spices, vegetable seasoning, poultry and ground beef. Another 35 countries have approved some form of food irradiation but the biggest hurdle is consumer acceptance. Many consumers have misconceptions about the technology and believe that it makes food radioactive. However, this is not so because food does not become radioactive with irradiation.
Potential uses of Food Irradiation
|Type of Food||Effects of Irradiation|
|Meat, poultry||Destroys pathogenic organisms, such as Salmonella, Campylobacter and Trichinae|
|Perishable foods||Delays spoilage; retards mold growth; reduces number of microorganisms|
|Grain, fruit||Controls insect vegetables, infestation dehydrated fruit, spices and seasonings , Reduces rehydration time|
|Onions, carrots, potatoes, garlic, ginger||Inhibits sprouting|
|Bananas, mangos, papayas, guavas, other non-citrus fruits||Delays ripening avocados, natural juices|
How does irradiation affect the food itself?
Ionizing radiation breaks some of the chemical bonds within the food itself. The effects of chemical changes in foods are varied. These effects are the result of radiolysis. Whether the products of radiolysis in food are all harmless from a human health perspective is still debated. However, from years of experience in food irradiation it is seen that there are no identifiable health problems. Some changes in foods may not be good but others can be. Examples of some food changes are:
- changes in structure of certain foods too fragile to withstand the irradiation, for example, lettuce and other leafy vegetables turn mushy
- slowed ripening and maturation in certain fruits and vegetables lengthens shelf-life
- reduction or destruction of some nutrients, such as vitamins, reduces the nutritional value (the effect is comparable to losses in heat pasteurisation)
- alteration of some flavour compounds
- formation of compounds that were not originally present requires the strict control of radiation levels
- generation of free radicals, some of which recombine with other ions.
As per FSS Act (2006) regulation 2.4.4 describes the labelling of irradiated food. The labelling of pre-packed irradiated food shall be in accordance with the provisions of FSS (Packaging & Labelling) Regulations. Also, the provisions of the atomic energy (control of Irradiation of Food) Rules, 1991, under the Atomic Energy Act, 1962 should be followed.
All packages of irradiated food shall bear the following declaration and logo, namely: –
|PROCESSED BY IRRADIATION METHOD…………………………………………………….
DATE OF IRRADIATION………………………………………………………………………….
|LICENSE NO of Irradiation Unit…………………………………………………………………PURPOSE OF IRRADIATION…………………………………………………………………….|
In India, the standard guidelines for Irradiated Food Products have been defined under Food Safety and Standards (Food Products Standards & Food Additives) Regulations, 2011.
Irradiated foods require proper food handling
Food irradiation can only be used if it fulfills a technological need or is necessary for food safety or food hygiene. It cannot replace the need for correct food handling practices in the food industry. Some bacteria may survive the irradiation of food, for example meat, so if meat is left unrefrigerated or not handled according to food safety norms, these bacteria could multiply and cause food poisoning. Irradiated foods need to be stored, handled and cooked in the same way as foods that are not irradiated and according to good food handling practices.