Radiation processing or food irradiation is a technique of food preservation. It is performed by applying ionizing radiation to food in order to reduce or inactivate microorganisms and insects. Apart from dis-infection, pest control and sterilization, irradiation of food also helps in shelf-life extension and sprout inhibition.
Source of Radiation:
- Cobalt-60 – This gamma ray emitter is the most commonly used modality.
- Electron Beams.
- X-rays.
Gamma rays are preferred for non-uniform and thicker materials as they have a deeper penetration.
Mechanism of Action:
When these waves enter the food item, they collide with the particles they come across. Chemical bonds are broken, thus producing short lived radicals. These radicals bond with or strip nearby molecules that leads to more changes. Collisions in cells inhibits cell division and retards the process that enables food to mature. When DNA or RNA is damaged, it halts the growth of pathogens.
Is irradiated food radioactive?
The food item is exposed to ionizing radiation for a pre-determined time in order to impart a prescribed dose.
The radioactive sources do not produce gamma rays, electrons or X-rays of sufficient high energy to make food become radioactive.
In a hospital, a person undergoing a diagnostic X-ray does not make him radioactive; in the same way food irradiated is not radioactive.
Safety of Irradiated Foods – International Standards
In 1920, a German named Otto Wust discovered that food could be preserved by exposing it to ionizing radiation.
The U.S. Food and Drug Administration (FDA) the World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC) and U.S. Department of Agriculture (USDA) have carried out studies that have proved and confirmed the safety of food irradiation.
The Codex Alimentarius represents the global standard for irradiation of food. The International Atomic Energy Agency (IAEA), Nuclear Regulatory Commission (NRC), the International Organization for Standardization (ISO), ISO 14470 and ISO 9001 have set safety standards that all processing facilities must follow.
The American Dietetic Association and Scientific Committee of European Union are internationally recognized bodies that support food irradiation.
Benefits of Food Irradiation:
- Prevention of food poisoning: Irradiation of food eliminates pathogens like Salmonella, Compylobacter, Listeria, Escherichia coli (Ecoli) and parasites.
- Enhancement in shelf life of foods: Irradiation inactivates germs that cause decomposition.
- Insect disinfestation: Not only does irradiation destroy insects, but it also thereby decreases the need for pest-control practices that can be harmful.
- Inhibit of sprouting in bulbs, tubers and rhizomes.
- Increase fruit longevity by delaying the ripening process.
- Lowers the risk of transmission of insect pests during import and export of food.
- Sterilization: Foods sterilized by irradiation can be stored without refrigeration for years. They are useful for patients with severely damaged immune systems, such as patients with AIDS or patients undergoing chemotherapy. NASA (National Aeronautics and Space Administration) astronauts consume meat that is irradiated to avoid falling ill in space.
Dose of Radiation:
Low Dose (<1 kGy): Radicidation
Process Dose (kGy)
To inhibit sprouting 0.02-0.2 kGy
To delay ripening 0.2-1 kGy
Insect control 0.25-1 kGy
Medium Dose (1-10 kGy): Radurization
Process Dose
To improve shelf life 1-3 kGy
To eliminate pathogens 1-7 kGy
Spices Higienization 6-14 kGy
High Dose (> 10 kGy): Radapperization
Packaged Food Sterilization 5-25 kGy (Hospital Diets)
Advantages of Radiation Processing:
- Being a cold process, it can be used on farm products without altering its fresh-like character.
- This process does not cause a significant change in the flavor, appearance and nutritional value of food.
- Unlike chemical fumigants, radiation does not leave any toxic radioactive residue on the food.
- The food treated does not become radioactive.
- Food irradiation is a very effective method.
- Pre-packaged foods can be treated for enhancing its shelf life.
Limitations of this Technology:
- This technology cannot be applied to all foods. For example, dairy foods and eggs cannot be irradiated as it changes its flavor and texture.
- Food irradiation cannot turn an already spoiled or overripe food into a fresh state.
- It has no effect on pesticides and toxins present in the food already. For instance, Clostridium botulinum a bacteria releases a toxin that leads to botulism. Food treated with radiation can control the growth of C. botulinum bacteria, but cannot remove its toxin.
- Food irradiation is not effective against all viruses.
Phytosanitary Irradiation:
The use of ionizing radiation on foods and vegetables in order to inactivate insects is known as phytosanitary irradiation. This technique is used for international food trade to prevent the spread of non native organisms.
Radiation Processing of Food:
1. Sprout Inhibition:
Rhizomes, bulbs and tubers tend to sprout naturally when they are stored. The sprouts lose weight and hence even marketability.
Radiation processing can be done for onion, fresh ginger, potato and shallots. For these commodities, irradiation is carried out to control sprouting alone and not to eliminate micorbes causing rot.
Following irradiation, onion may have a brownish discoloration in its inner bud. This however, has no effect on its usage.
2. Delay the Ripening of Fruits such as Mango and Banana:
The primary purpose of irradiating mango and banana is to extend its shelf-life by delaying ripening. Apart from this, irradiation also decreases the spoilage microbes and insects prevalent in these fruits.
Banana: A minimum delay of 7-8 days is obtained after radiation processing. It is best to store the fruits at lower temperatures after irradiation.
Mango: A 7-14 day delay in ripening is achieved following irradiation. Just like banana, it is advisable to store the fruits at lower temperatures.
3. Insect Disinfestation & Microbial Elimination of Spices, Herbs and Dry Vegetables:
Spices, herbs and dry vegetables are subject to a dose of 10 kGy for decontamination and disinfestation. This dose of radiation, will bring the bacterial load down to 0-100 CFC (Colony Forming Units), which is within the safe levels.
It is advisable to pre-package the spices, herbs and dry vegetables prior to irradiation, to prevent recontamination and re-infestation.
Packaging material impervious to insect pests must be used. The item should be packed in its final distribution form and then subject to irradiation. This will enable the product to last up to 1 year or more after radiation processing.
4. Cereals, Pulses, Grain Products: Insect Control
Insects damage rice, wheat, pulses and products such as wheat flour, semolina and pulse products. Insects increase the moisture which in turn leads to microbial growth. The commodity must be packaged with impervious material and then sent for irradiation. This will avoid post-processing contamination.
5. Dry Fruits and Raisins Disinfestation:
Insects attack dry fruits and raisins that leads to huge economic loses. Radiation destroys the metamorphic stage of the insects and halts the damage. The commodity should be packaged with insect proof material before radiation processing to avoid re-infestation after irradiation.
6. Improvement of Shelf-life of meat and Poultry:
Raw meat products, either fresh or frozen can be irradiated to decontaminate it from spoilage microbes and parasites (protozoa and helminthes). Irradiation also enhances the shelf-life of fresh meat.
Slaughtering only healthy animals, following hygienic practices while dressing the meat, promptly reducing the temperature to 4oC or below and appropriate cutting and deboning operations are recommended by the International Codes for GMP (Good Manufacturing Practices). Frozen meat should be kept below -20oC.
Protective packaging should be done before the radiation processing. Vacuum and inert packaging is advisable. The packaged meat mush be stored below 4oC to prevent the risk of botulism.
7. Fish and Shrimp: Microbial Control:
Irradiation of frozen fish and shrimp inactivates pathogens. The meat must be in functionally protective package prior to irradiation. Radiation processing of fresh fish and shrimp decreases the pathogens and enhances the shelf-life, when stored under refrigeration. The seafoods must be dressed, handled and stored as per GMP. Vacuum packaging is ideal as it avoids non-bacterial spoilage.
Botulism can be prevented by storing fresh fish below 3oC. Frozen fish and shrimp must be kept below -20oC during irradiation and post-processing.
8. Dried Fish: Disinfestation
Insects feed on dried fish and cause financial loss. Irradiation helps in disinfestation. This does not however prevent mould growth. The methods of salting the fish, using preservatives and following good manufacturing practices must be adopted to maintain the quality of the fish before irradiation. The dried fish must be packaged in impervious material. Use of packaging under vacuum and inert atmosphere renders better results. The moisture level must be kept below 14% throughout. Irradiated dry fish can be stored for 6-9 months.
Re-irradiation
Foods with low moisture content can be re-processed by radiation in order to control insect re-infestation. These foods include cereals and pulses. The cumulative overall average dose absorbed must not exceed 10 kGy from the first and second irradiation process.
How Do We Know if the Food is Irradiated?
As per the FDA guidelines, irradiated foods are labelled with the “Radura Symbol.” They will also carry the statement “Treated with radiation” or “treated by irradiation.”
Conclusion:
Food Irradiation is a technology by which agricultural items in pre-packed condition are exposed to controlled radiant energy for a desirable effect. The food does not become radioactive. Irradiation is not a replacement for hygienic food handling practices. Irradiated foods could become contaminated with pathogens after irradiation if the basic rules of food safety are not implemented.