Food Irradiation

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“Food irradiation exposes certain types of food to a source of ionising energy. Under the standard covering the irradiation of food in Australia, this energy can be in the form of Cobalt 60-sourced gamma rays, machine-generated X-rays, or an electrically generated electron beam”  (www.consumersonline.gov.au/content/food/Irradiated.asp).  Irradiation does not significantly increase the temperature or change the physical or sensory characteristics of most foods. An irradiated apple will still be crisp and juicy. However, irradiation cannot be used with all foods. It causes undesirable flavour changes in dairy products and it causes tissue softening in some fruits, such as peaches and nectarines.

How does it work?

All ionizing radiation is able to remove an electron from an atom or molecule making it highly reactive. The reactive molecules react with other molecules damaging the cell’s molecular machinery and processes. Most cellular machinery can be effectively repaired. However high doses can be sufficient to destroy cells outright. Cells in the process of replication are more severely affected than other cells. The molecular damage:  Inhibits sprouting; Delays ripening and ageing; Kills or sterilises some insects and parasites; Reduces the levels of bacteria and therefore increases shelf life.

Methods
1. Electron beam irradiation
“Electron beam irradiation uses electrons accelerated in an electric field to a velocity close to the speed of light. Electrons do not penetrate the product beyond a few inches, making it necessary to treat fruit and vegetables individually; on the other hand, treatment times are only a few seconds.” (Wikipedia).

2. Gamma radiation
“Gamma radiation is radiation of photons in the gamma part of the spectrum. The radiation is obtained through the use of radioisotopes, generally cobalt 60 or in very few cases cesium 137. It is the most cost-effective technology and is preferred by many processors because the good penetration enables administering treatment to entire industrial pallets or totes, greatly reducing the need for material handling. A pallet or tote is typically exposed for several minutes depending on dose.” (Wikipedia).

3. X-Ray irradiation “Similar to gamma radiation, x-rays are a lower-energy substitute for the former. These systems are scalable and have good penetration, with the added benefit of using an electronic source that stops radiating when switched off. They also permit very good dose uniformity. However these systems require a great deal of electrical energy when operating, and exposure times are longer than with gamma rays.”

“Radioactive materials usually release alpha particles (helium nuclei), beta particles (quickly moving electrons or positrons) or gamma rays. Alpha and beta rays can often be shielded by a piece of paper or a sheet of aluminium, respectively.” “Gamma rays are less ionizing than either alpha or beta rays, but protection against them requires thicker shielding. They produce damage similar to that caused by X-rays such as burns, cancer, and genetic mutations”. (Wikipedia).

The energy waves are not retained in the food just as food cooked in a microwave oven or teeth and bones that have been X-rayed do not retain those energy waves.

Dosage    

Levels of absorbed radiation are currently measured in kiograys (kGy). The scientific community has defined three levels of food irradiation:

• Low dose up to 1kGy – kills insects on fruit and grain and kills or prevents the maturation of Trichinella • Medium dose 1-10 kGy – kills most of the bacteria that cause foodborne illness (1.5-3.0kGy for poultry)

• High dose 10+kGy can sterilize meat and other foods and decontaminate herbs and spices.

Is it new?  
The process was patented for food preservation in 1905 by a French scientist. American research began in 1921 when the U.S. Department of Agriculture (USDA) reported that irradiation would effectively kill trichinae in pork. Since then, it has gradually gathered momentum with improvements in the technology and the need for new methods to combat foodborne illness. http://www.fmi.org/media/bg/irradiation.pdf

Nutrient loss 
Many of the molecules our body requires can be made (nouveau) from the broken molecular bits and pieces absorbed via our digestive tract. However there are some nutrients we can’t make from scratch. Most animals don’t need to eat Vitamin C because they can make it. We have the genes to make it but one does not work due to mutation. We therefore need to consume food containing Vit C to remain healthy. There are many nutrients we cannot make from scratch so it is important that our food contains them.

A joint FAO/IAEA/WHO study concluded that ‘food irradiated to any dose appropriate to achieve the intended technological objective is both safe to consume and nutritionally adequate’. The Australia New Zealand Food Safety Council (ANZFSC) stated that irradiated foods will not have any significant impact on the average dietary intakes of essential vitamins and minerals. Charlotte P. Brennand, PhD, Extension Food Safety Specialist March 1995 FN-250.8 states, “nutritional losses are less than or about the same as cooking and freezing”.
Most sources approximate 5- 10% of Vitamin C is lost due to food irradiation.

Table 1. Vitamin content comparison of cooked chicken (irradiated and not irradiated). Amounts are for 2.2 pounds (1 kilogram) cooked chicken. Reference: Journal of Food Processing and Preservation 2:229, 1978.

Radioactive food Some people are concerned that irradiated food will be made radioactive. “Radioactivity [is the] disposition of some elements to undergo spontaneous disintegration of their nuclei associated with the emission of ionizing particles and electromagnetic radiation, as alpha particles or Beta particles and gamma radiation” (Henderson’s Dictionary of Biological terms 10th Edition Eleanor Lawrence). According to Charlotte P. Brennand, PhD, Extension Food Safety Specialist “the ionizing radiation used by [food] irradiators is not strong enough to disintegrate the nucleus of even one atom of a food molecule”.   The irradiation process involves passing food through an irradiation field; however, the food itself does not ever contact a radioactive substance.

Don’t be concerned about “interesting human mutations” occurring as a result of eating irradiated food. Food irradiated in the standard way cannot pass on radioactivity let alone radioactivity that will cause DNA damage.

It is physically impossible for food to become radioactive due to the process of food irradiation just as your teeth do not become radioactive after you have had a dental X-ray. Irradiation is radiant energy. It disappears when the energy source is removed.

Genetically damaged food
“Interesting human mutations” will not occur as result of eating genetically damaged food. A genetic mutation cannot be caught like a cold.  Depending on the type of irradiation used, DNA within the food may or may not be damaged. “Gamma or neutron irradiation is often used in conjunction with other techniques, to produce new genetic lines of root and tuber crops, cereals and oil seed crops. New kinds of sorghum, garlic, wheat, bananas, beans and peppers are more resistant to pests and more adaptable to harsh climatic conditions. In Mali, irradiation of sorghum and rice seeds has produced more productive and marketable varieties.” http://www.uic.com.au/peac.htm.

Radiolytic contamination                                                                                                              
Any kind of treatment causes chemical changes in food and that includes irradiation. The substances produced by irradiation are called radio-lytic products just as the chemicals produced by cooking could be called thermo-lytic products.

“Irradiating meat can produce benzene” and “irradiating carbohydrate-rich foods can yield formaldehyde”. Radiolytic products can be found in “cooking, canning and pasteurisation”. “At prescribed dosage levels irradiation produces small amounts of such compounds”. http://www.fmi.org/media/bg/irradiation.pdf
Scientists find the changes in food created by irradiation minor to those created by cooking. See Charlotte P. Brennand, PhD, Extension Food Safety Specialist March 1995 FN-250.8 or look up Cytochrome p450 enzymes (multi-purpose enzymes that often handle thermolytic products and more).

If you are serious about not eating irradiated food because of radiolytic products you should be serious about giving up cooked food.

Some people are concerned that irradiation will result in the formation of stereoisomers. Stereoisomers are molecules that are constructed with the same atoms but the arrangement differs in such a way that the molecules are mirror images (of each other) that cannot be superimposed (just like a left and right hand). A left-hand glove does not fit a right hand. This property is known as chirality. All but one of the 20 naturally occurring amino acids (building blocks of proteins) are chiral and are made naturally in a ‘left-handed’ form. Molecules of natural sugars are almost all made naturally in the ‘right-handed’ form (including the sugar that occurs in DNA). When molecules are manufactured in a biological system usually only one of the stereoforms is made (eg. ribose is usually made right-handed) however whenever these molecules are synthesised artificially, approximately 50% will be one stereoform and 50% will be the other. This can be a problem for the body as it is prepared to handle the naturally occurring form. This is what happened in the Thalidomide fiasco. One of the Thalidomide stereoisomers can be easily cleared by the body the other is not easily cleared. Nowadays regulated pharmaceuticals have the non-biological isomer product removed so that the body can remove the drug.

So if you are worried about irradiation because of stereoisomer formation then you shouldn’t be buying unregulated tablets or capsules of Vitamin E, synthesised amino acids or synthesised sugars unless you know the stereoisomers have been removed.

Old molecules synthesised biologically are known to flip (to the other isomeric form) for no apparent reason.

So if you are concerned about stereoisomers you should think twice about consuming any ‘old’ food eg. herbs that are not freshly picked.

The problems with stereoisomers are well known and regulated in the pharmaceutical industry. Since irradiation is regulated I would hope any problem of stereoisomer formation would have been taken into consideration. “Independent scientific research on the subject [radiolytic products produced by food irradiation] has been extensive, leading to endorsement of food irradiation by the US Food and Drug Administration, the United States Department of Agriculture and the U.N. World Health Organization as a safe, effective process”.  “The effects of food irradiation have been studied for over 60 years.” Wikipedia.

What irradiated foods are currently approved in Australia and New Zealand?   Approval was granted in September 2001 for the use of irradiation on herbs, spices and herbal infusions for control of microbes and for reduction of pests of quarantine concern.  In March 2003 the Food Standards Code was changed to allow the irradiation of the tropical fruits: breadfruit, carambola, custard apple, litchi, longan, mango, mangosteen, papaya and rambutan as a pest disinfestation measure for pests such as the fruit fly. The permission is for irradiation to a maximum of 1 (kGy) from machine-sourced electron beams or x-rays, employing Good Manufacturing/Irradiation Practices. Irradiated tropical fruits require mandatory labelling.

http://www.foodstandards.gov.au/mediareleasespublications/factsheets/fac…

Irradiated Foods Overseas:
More than 50 countries have approved irradiation for about 50 products according to the International Atomic Energy Agency (IAEA), and 33 are irradiating foods and spices commercially.

Chile irradiates about 130 metric tons (mt) per year, mostly spices, according to Nordion. Russia treats 400,000 mt each year, mostly to eliminate insect infestations from imported grain coming into its port of Odessa. China irradiates garlic to prevent sprouting and Japan treats potatoes for the same reason. France irradiates poultry to control contamination. http://www.fmi.org/media/bg/irradiation.pdf.

Conclusion: Fresh is best but I would not say “no” to an irradiated apple.

Sites of interest:

http://www.foodstandards.gov.au/mediareleasespublications/factsheets/fac…
http://www.consumersonline.gov.au/link.asp?URL=http://www.foodstandards….
http://www.dakibudtcha.com.au/Narangbah%20Irradiation%20Plant.htm

Note from Sheryl:   Tirsha has been an active member of our Club for a number of years and is also a member of the Skeptics, The Mycological Society of Queensland, a bookclub and other organisations. Her background is in biochemistry, genetics, aviation, minerals and education. She is currently a ‘Project Scientist’ at CSIRO at Pullenvale.