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How Does Food Irradiation Work?

Ever since the FDA approved the use of irradiation on leafy greens last week, I've been curious to find out how irradiation works as well as its drawbacks. Where does anyone start when they want to find basic information on any topic? Wikipedia, of course.
Food irradiation is the process of exposing food to ionizing radiation in order to destroy micro-organisms, bacteria, viruses, or insects that might be present in the food.


The genuine effect of processing food by ionizing radiation relates to damages to the DNA, the basic genetic information for life. Micro-organisms can no longer proliferate and continue their malignant or pathogen activities.


By irradiating food, depending on the dose, some or all of the harmful bacteria and other pathogens present are killed. This prolongs the shelf-life of the food in cases where microbial spoilage is the limiting factor.


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. A pallet or tote is typically exposed for several minutes to hours depending on dose. Radioactive material must be monitored and carefully stored to shield workers and the environment from its gamma rays. During operation this is achieved by substantial concrete shields.
Does food become radioactive after its irradiated?

No. The only way it becomes radioactive is if the source (Cobalt-60) gets on the food, which doesn't happen.

What are the criticisms?

Gristmill and Treehugger (reasonable go-to sources for anti-nuclear claims) published their thoughts last week on the FDAs recent approval.

Gristmill didn't really have complaints on irradiation itself, only that "the FDA is missing the fundamental key to "food safety" -- the prevention of contamination from happening in the first place." Well, people had the same concerns when pasteurization was first introduced (pdf, p. 15), now pasteurization is widely accepted. If you could make food safer and last longer, why not? No amount of prevention will get rid of all the organisms living on the food. Irradiation does.

Treehugger had more interesting comments, most of them in favor of irradiation. Here's one of the criticisms:
Irradiation works by splitting chemical bonds in molecules with high energy beams to form ions and free radicals. When sufficient critical bonds are split in organisms contaminating a food, the organism is killed. Comparable bonds are split in the food. Ions are stable; free radicals contain an unpaired electron and are inherently unstable and therefore reactive. ... I am opposed to consuming irradiated food because of the abundant and convincing evidence in the referred scientific literature that the condensation products of the free radicals formed during irradiation produce statistically significant increases in carcinogenesis, mutagenesis and cardiovascular disease in animals and man.
Sounds scary. Here's what the IAEA says about free radicals (pdf, p. 26):
The fact that irradiation causes the formation of free radicals - which in scientific terms are atoms or molecules with an unpaired electron - and that these are quite stable in dry foods has often been mentioned as a reason for special caution with irradiated dry foods. However, free radicals are also formed by other food treatments, such as toasting of bread, frying, and freeze drying, and during normal oxidation processes in food. They are generally very reactive, unstable structures, that continuously react with substances to form stable products. Free radicals disappear by reacting with each other in the presence of liquids, such as saliva in the mouth. Consequently, their ingestion does not create any toxicological or other harmful effects.
So I haven't found any real drawbacks to irradiation, only a lot of benefits. As irradiation becomes more and more accepted, hopefully more and more people will become less afraid of radiation. Radiation needs to be understood, not feared. Like I said before, radiation saves lives.


Mike Sivertsen said…
Glad the FDA finally got around to approving leafy vegetables. Now what about the peppers?

Your readers may find a post I wrote about food irradiation in June 2008 informative.

Food Irradiation Can Save Lives and Reduce Medical Costs
DV8 2XL said…
The use of radiation in food processing is by no means new. Meats, fish, fruits and vegetables have been preserved for centuries by the sun’s energy. Lately, infrared and microwave radiation has been added to the list of radiant energies in food processing.

While the term irradiation pertains to all forms of treating products with ionizing radiation, specific types of radiation treatments depend on the objective and the item being processed

Radurization is the process of pasteurization by the use of radiation. It primarily used to treat foods that have a high moisture content and a high pH. The microbes that are targeted are mainly spoilage organisms. Meat and fish are the foods for which this process is mainly used. For dryer, acidic foods, yeasts and molds can be denatured. The treatment dose for radurization is approximately 1 kGy

The process of radicidation is used to eliminate pathogens and insect pests. This process kills cells only, meaning that it will not kill spores. Also, certain radiation-resistant vegetative cells can survive, including some strains of the bacterium Salmonella which have been found to be radiation-resistant. The dose for radicidation ranges from 2.5 - 5.0 kGy.

These first two require that the food be refrigerated post-treatment.

Radappertization involves treating the product to levels of radiation of approximately 30 kGy. This high level of radiation also destroys spores from organisms such as Clostridium botulinum, Such levels are generally deemed sufficient for clinical sterility, but not usually employed on food items.

It is this last level where chemical changes occur, which can impact flavor and appearance, and where 'free radicals' can be said to form.

Consequently, based on recommendations of the International Consultative Group on Food Irradiation that was formed by the joint FAO/IAEA division many national legislation limit applicable doses to 10kGy for many food items.

However note that in the Republic of South Africa precooked, shelf-stable meat products irradiated at 45 kGy are allowed for retail sale. These have been available for years with no reports of adverse effects to consumers.

As is usual in nuclear energy matters the critics want everyone to believe that this technology hasn't developed any further from where it began in the 1950's in military food research programs and problems and issues that were seen then have not been eliminated.

To date, food irradiation has been studied more than any other food process. All evidence gathered from scientific and technical research leads to the conclusion that food irradiation is a safe, beneficial and practical process.

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