Table of Contents
- Introduction to Food Irradiation
- Significant events in the history of food preservation by Irradiation
- Radiation dose
- Different forms of irradiation treatment for sterilization
- Three kinds of radiation are used in irradiators
- Factor affecting food irradiation treatment.
- Features of food Irradiation
- Principle of food irradiation
- Application of Irradiation in Foods
- How is food irradiated?
- Disadvantages of Food irradiation
- References
Introduction to Food Irradiation
- Food irradiation is a food preservation technique in which food is exposed to ionizing radiation beams such as gamma rays, electron beams, and X-rays to eliminate food spoilage microorganisms, pathogenic microorganisms, pests, and insects.
- This technique extends the shelf life of fresh fruits and vegetables by controlling natural processes including ripening, maturation, sprouting, and aging.
- The process of food irradiation is also referred to as cold sterilization (or pasteurization) because it does not produce significant heat; as a result, the nutritional and organoleptic properties of food are preserved in comparison to other thermal techniques.
- Radiation refers to the number of photons emitted from a single source, whereas irradiation refers to the process of exposing the emitted photons or radiation to the surface of food.
- A predetermined irradiation dose can be applied to food, either in prepackaged form (meant for direct consumption) or in bulk containers.
- Irradiated food is required to be labeled with the international logo, mentioning either “irradiated food” or “treated with ionizing radiation.”
Significant events in the history of food preservation by Irradiation
- 1895 – Discovery of X-rays.
- 1905 – The first patent is granted for the use of ionizing radiation in food preservation.
- 1950 – Scientific research on food irradiation begins.
- 1953 – The first commercial application of food irradiation is introduced.
- 1958 – The U.S. Food and Drug Administration (FDA) grants approval for using irradiation to sterilize food products.
- 1963 – FDA approves irradiation specifically to control insect infestation in wheat and wheat flour.
- 1980 – The Codex Alimentarius adopts international guidelines for the application of irradiation in food preservation.
- 1986 – FDA approves the use of irradiation to control Trichinella parasites in pork products.
- 1990 – Irradiation is approved for controlling pathogens in meat and poultry.
- 1990s – The European Union (EU) approves irradiation for insect disinfestation and microbial decontamination of spices and herbs.
- 2000 – Irradiation is approved for use on shell eggs.
- 2003 – The World Health Organization (WHO) and the International Atomic Energy Agency (IAEA) issue a joint statement endorsing both the safety and efficacy of food irradiation.
Radiation dose
- The quantity of radiation energy absorbed by food is known as the radiation dose.
- The unit used to measure radiation dose is called the gray (Gy).
- 1 Gy is defined as the absorption of one joule of radiation energy per kilogram of food.
- According to the CODEX General Standard for Irradiated Food, the maximum radiation dose delivered to food should not exceed 10 kGy.
- In the United States, the Food and Drug Administration (FDA) regulates both the source of radiation and the dose of radiation applied to food.
- The selection and use of an appropriate radiation dose is the most critical factor in ensuring the effectiveness and safety of food irradiation.
Different forms of irradiation treatment for sterilization
Radurisation (radiate, prolong):
- A type of radiation treatment used to extend or prolong the shelf life of food products during storage while maintaining their natural quality.
- The primary aims include inhibiting germination, providing pest control, slowing down sprouting, and destroying pathogenic parasites and microorganisms.
- This method applies a low dose of radiation.
Radicidation (radiate, kill):
- A radiation treatment that uses higher doses of radiation to selectively kill specific microorganisms, such as Salmonella.
- The applied radiation dose ranges between 2–10 kGy, which is considered technically safe for human health.
- This process ensures microbial safety without compromising the edibility of food products.
Radappertisation (radiate, canning food):
- A form of industrial sterilization that involves applying the highest doses of radiation (10–50 kGy) to eliminate all microorganisms present in food products.
- Specially designed for canned food manufacturers.
- Commonly applied to the sterilization of spices, meat products, and dietetic foods intended for sick or immunocompromised individuals.
Three kinds of radiation are used in irradiators
Gamma rays from radionuclides (⁶⁰Co or ¹³⁷Cs):
- A type of ionizing radiation emitted from radionuclides.
- Have a high penetration capacity.
- Suitable for applications on an industrial scale.
Electron beams from machine sources:
- Generated by electron accelerators.
- A relatively low-cost option.
- Have a maximum penetration depth of about 8 cm.
- Most effective when applied to food products spread in a thin layer.
X-rays from machine sources:
- Produced by an X-ray generator.
- Provide good penetration capacity, superior to electron beams.
Factor affecting food irradiation treatment
- Type of food: Different foods vary in composition (moisture, fat, protein, and carbohydrate content), which influences how radiation interacts with the product and affects treatment efficiency.
- Radiation dose: The amount of absorbed radiation (measured in grays, Gy) determines the extent of microbial inactivation, pest control, and shelf-life extension.
- Treatment plant design: The layout, type of irradiator, radiation source, and method of food handling during treatment play a significant role in achieving uniform and effective irradiation.
- Exposure time and temperature: The duration of exposure to radiation and the temperature conditions during treatment affect both microbial reduction and the preservation of food quality.
Features of food Irradiation
- Cold sterilization: Food irradiation is considered a cold process because it does not generate significant heat during treatment.
- Effective in lengthening shelf life: It efficiently extends the storage life of fresh fruits and vegetables by slowing down natural processes and reducing microbial spoilage.
- Green technology: Recognized as an environmentally friendly method for food preservation.
- Nutritional stability: The nutritional value of irradiated food remains stable, with minimal impact on vitamins and other essential nutrients.
- Minimal quality loss: There is very little change in the texture, flavor, aroma, and color of the food.
- Non-radioactive: Irradiation does not make food itself radioactive, ensuring safety for consumption.
Principle of food irradiation
Generation of ionizing radiation:
- Machines such as electron accelerators, X-ray generators, or radionuclides are designed to generate safe ionizing radiation for food treatment.
- Accelerated electron beams can penetrate food up to 8 cm.
Direct effect of radiation:
- Occurs when electromagnetic radiation or particle beams directly strike molecular complexes in biological material.
- This interaction can alter or destroy biological functions, potentially causing chromosomal disorders or mutations.
- However, in the context of food preservation, the direct effect is considered less important.
Indirect effect of radiation:
- Ionizing radiation interacts with atoms in high-moisture foods, leading to the radiolysis of water.
- This produces free radicals such as hydrogen (H·) and hydroxyl (OH·) radicals, which further combine to form hydrogen, hydroxy, and hydroperoxyl radicals.
- Oxygen reacts to produce hydroperoxyl radicals, which play a major role in microbial inhibition due to their oxidative action.
- These radicals interfere with biochemical reactions and alter molecular structures by:
- Breaking single- and double-stranded DNA molecules.
- Abstracting hydrogen and eliminating phosphate groups.
- Hydroxylating purine and pyrimidine bases.
Reactions involved in the radiolysis of water:
Ionization of water:
H₂O + energy → H₂O⁺ + e⁻
Formation of hydroxyl radical:
H₂O⁺ + e⁻ → H⁺ + OH·
Formation of hydrogen radical:
H₂O + e⁻ → H· + OH⁻
Recombination reactions:
H· + H· → H₂
OH· + OH· → H₂O₂
Other reactions:
H· + OH· → H₂O
H· + H₂O → H₂ + OH·
OH· + H₂O₂ → H₂O + HO₂·
H· + O₂ → HO₂·
HO₂· + HO₂· → H₂O₂ + O₂
Application of Irradiation in Foods
General applications of food irradiation:
- Delays the ripening of green bananas.
- Inhibits the sprouting of potatoes and onions.
- Prevents the greening of potatoes.
- Softens legumes and reduces their cooking time.
- Increases the yield of juices from grapes.
- Speeds up the drying rate of plums.
Radiation dose ranges and their specific applications:
- 0.05 – 0.15 kGy: Applied to potatoes, onions, garlic, and yams for inhibition of sprouting.
- 0.1 – 0.3 kGy: Applied to meat for the destruction of parasites.
- 0.1 – 0.5 kGy: Applied to grains, flour, coffee beans, and dried fruits for insect disinfestation.
- 1.0 – 5.0 kGy: Applied to fruits and vegetables for the reduction of microorganisms.
- 0.5 – 1.5 kGy: Applied to mushrooms and fruits to delay maturation.
How is food irradiated?
- Food irradiation is carried out in a specially designed facility called an irradiator, which ensures safety and controlled exposure.
- The food to be treated can be either prepackaged for direct consumption or placed in bulk containers.
- The food packages are placed on a conveyor system that moves them into the irradiation chamber.
- Depending on the type of source used, the irradiation process can involve:
- Gamma rays (from radionuclides such as Cobalt-60 or Cesium-137), which provide deep penetration and are suitable for bulk or industrial-scale treatment.
- Electron beams, generated from electron accelerators, which are lower cost but have limited penetration (up to ~8 cm), making them effective for thin-layered foods.
- X-rays, generated from X-ray machines, which have good penetration capacity (intermediate between gamma rays and electron beams).
- Inside the chamber, the food is exposed to a predetermined radiation dose, measured in grays (Gy), ensuring microbial destruction, pest control, or delayed ripening depending on the objective.
- The radiation energy passes through the food, disrupting microbial DNA and cellular processes, but it does not make the food radioactive.
- After irradiation, food is removed from the chamber, checked for labeling, and packaged or distributed.
- International regulations require that irradiated foods be labeled with the Radura symbol and the statement “Treated with ionizing radiation” or “Irradiated food.”
Disadvantages of Food irradiation
- High initial cost: Establishing irradiation facilities and equipment requires a significant investment.
- Public perception: Many consumers remain skeptical or fearful of irradiated foods due to misconceptions about radioactivity.
- Changes in sensory properties: In some foods, irradiation can cause slight alterations in texture, flavor, aroma, or color.
- Regulatory issues: Approval and implementation of food irradiation vary between countries, making international trade complicated.
- Limited effectiveness: The process is less effective against certain microorganisms, such as viruses and prions.
- Risk of unintentional over-irradiation: Incorrect dose application can compromise food quality and safety.
- Irradiation-resistant microorganisms: Some resistant strains may survive and produce toxins.
- Potential for harmful by-products: In rare cases, chemical changes may lead to the formation of undesirable compounds.
- Mandatory labeling: Irradiated food must be labeled with the Radura symbol along with the statement indicating it has been treated with ionizing radiation.
References
- Potter, N. P. (1987). Food Science. CBS Publishers, India.
- Rahman, M. S. (1999). Handbook of Food Preservation. Marcel Dekker, Inc., New York.
- Desrosier, E. N. (1963). The Technology of Food Preservation. AVI Publishing Company, New York.
- Centers for Disease Control and Prevention (CDC). (n.d.). Food Irradiation. Retrieved from https://www.cdc.gov/foodsafety/communication/food-irradiation.html
