Food Irradiation, Threat to Our Health or an Ideal Alternative to Chemical/Heat Treatment? SuppVersity Kitchen Science

If you google images for food radiation, you get an idea of the (misplaced) prejudices against killing bacteria with ionizing radiation instead of nutrient damaging heat or potentially health-threatening chemicals -- No wonder companies still avoid it.
You may remember that I asked you to send in questions/research topics for the new SuppVersity Kitchen Science series in my recent article about different frying methods. Well, until now, the response has been - to be honest - disappointing. The first of the readers' suggestions I am going to address is Boban's question whether the (meanwhile) common practice of food irradiation is (a) sensible and (b) safe.

Now, I have to admit that the irradiation doesn't take place in the kitchen. I do, however, consider the act of grocery shopping part of "kitchen science"; after all, the choices you make in the super- or at the farmers' market will significantly affect the outcome of your "kitchen sessions".
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With that being said, let's briefly recap what exactly "food irradiation" is, what it is good for and what we know about potentially health-relevant effects on the irradiated food items. I guess that's also very necessary after all 78% of the US consumers in a recent study didn't even know that there are  "irradiated food" on the US market (Gwira Baumblatt 2017).

What is food irradiation?

Medicinet defines "food irradiation" as a "food safety technology designed to eliminate disease-causing germs from foods" (Medicinet). In other words, the foods are exposed to ionizing radiation, i.e. radiation that's strong enough to remove electrons from the individual atoms of both foods and germs, in order to kill the germs and parasites in and on foodstuff. Sounds bad? Well, that's what people thought in the wake of the nuclear bombing of Fukushima and Nagasaki, too.
"In this context, food irradiation was understood and termed as a nuclear technology (denounced as ‘atomic food’). The science had to answer those concerns, proving that irradiated food does not become radioactive. Once the process is conducted correctly and strictly controlled there will be no induced radioactivity" (Ehlermann 2016). 
As already hinted at, the process of "ionization" is not selective. Accordingly, there's little doubt that, in addition to modifying the molecular make-up of the cells of the germs and bacteria to a degree that renders them unviable, the radiation, usually gamma rays, electron beams, and X-rays, as well well as the use of lower frequency radiation in form of UV-A,-B and -C light will obviously have a certain effect on the structural qualities of food products.
Yes, irradiation will produce free radicals in food, but... even a glutton won't be able to eat enough of the foods actually ingest health-relevant amounts of  ‘free radials’. The small number of residual free radicals are also so short-lived in a humid environment that, at ingestion, they will just decay. Potentially not-negligible residual amounts of free radicals will only be found in very dry substrates from bones and shells which are not a compound of human nutrition - "in a typical human food, free radicals are contained only in an essentially negligible quantity" (Ehlermann 2016).
When we talk about these effects, the word "residual" is of paramount importance, because - that's the first good news - the three aforementioned types of radiation do, much in contrast to some hilarious claims on the Internet, not leave any traces on the irradiated goods. In other words: You don't have to be afraid of radioactive bananas or electron firing ground beef!

The question we have to answer, then, is not: "Is my food radioactive?" - the answer to this question would be a definitive "no" (it's even a problem to control if a food item was irradiated, because the process leaves no readily detectable traces), but rather: "Does the radiation change the original structure of the food in a way that could (a) reduce its nutritive value or, even worse, (b) turn a healthy cucumber into a health threat. You may already have noticed that the answers to both questions eventually come back to one important question:

Does food irradiation change the make-up or structure of the molecules in my foods?

In a time, where people still believe that microwaving would turn every food into a "Frankenfood", it's probably not hard to find "evidence" of such changes on alternative facts outlets like "". If you dig into the pertinent science databases, however, you will find a more balanced account of benefits and potential concerns. Accounts like Thayer's 1990 paper in the "Journal of Food Quality" in which he writes:
"The evidence supports the safety and efficacy of using ionizing radiation for insect disinfestation of grains; dried spices, vegetables and fruits; and fresh fruit. Species and dose dependent phytotoxic and vitamin changes may occur in some fruits at greater doses than currently approved by the U.S. Food and Drug Administration" (Thayer 1990).
For chicken, for example, the studies in review show that irradiation has no effect on the amino acid content of the meat and the MDA and peroxide levels of gamma- and electron-irradiated chicken is comparable to regular enzyme-inactivated frozen chicken. More recent studies in cheese show that there's no formation of potentially hazardous biogenic amines (Shalaby 2016)
Table 1: Whether or not irradiation should be the method of choice depends (among other things) on the intensity of the radiation dose that's required to inhibit sprouting, disinfect, kill parasites, etc. When more than 25kGy are necessary to do the trick, the advantage over other, chemical processes may vanish. Since this is the case, as you can see, only if you want to sterilize object like the scalpel in a doctors office, it's no reason for concern for the average consumer.
It is thus not surprising that the scientists were unable to detect genotoxic or teratogenic effects in mice, hamsters, rats rabbits - even if the animals were fed diets with an irradiated meat content of 70% or more.
Don't be fooled, you'll always lose something when you process foods: There are, for example, some vitamins that are particularly susceptible to radiation - for the fat soluble ones the order from the most to the least susceptible vitamins is vitamin E > carotene > A > D > K; for water-soluble vitamins it's B1 > C > B6 > B2 > folate, niacin, B12 (Diehl 1992). In a letter to the editor of the International Journal of Infectious Diseases, R. Kava does yet rightly point out that while "[n]o reputable nutritionist would deny that irradiation can lower the vitamin content of foods" the losses of thiamin from e.g. beef are less than that which occurs with canning or other thermal processing. And the often criticized loss of vitamin C in fruits and vegetables small relative to the natural variance in vitamin C content. Moreover, Kava highlights that pasteurization of milk results in losses of Vitamin B(- 12) (10%), thiamin (10%), Vitamin C (10-25%), and folic acid (10%), while irradiating the same product would have significantly less pronounced effects on its nutrient content.
Even though the results of these earlier studies are obviously still valid, it may make sense to a look at more recent evidence - after all, the technological advances of the last decades may make it possible for us to detect previously overlooked changes in irradiated food items that could - irrespective of any rodent safety study - be a problem:
  • The UV-C light vitners use to get rid of microbials will even significantly increase the resveratrol content of the skin of mature (A) and immature (B) grapes (Cantos 2000). Similar effects of UV rad. have been observed in apples, blueberries, mangos +other fruits.
    no effect on milk powder for formula at normal radiation levels - Tesfai, et al. (2014) reported three years ago in "Food Chemistry" that the irradiation of a milk-based infant formula did not change amino acid, fatty acid, and mineral profiles (Ca, P, Mg, Fe, Zn, Na, K) or trigger protein degradation; what they did observe, however, is that using irradiation levels of 25 kGy, or more, produced a significant increase in oxidized lipids and should thus be avoided
  • beneficial effects on mushrooms - mushrooms that were exposed to 2kGy of gamma-irradiation before storage hat significantly higher levels of phenolic compounds, when Beaulieu, et al. (1999) compared them to control samples over 9 days storage period
  • no effect on active ingredients of tumeric (curcumin & co) - while tumeric is a health food it's often full of unwanted bacterial and fungal contaminants, treating Curcuma longa L. with 10 kGy of gamma radiation takes care of the unwanted bugs and dose not affect the curcuminoids like curcumin, demethoxy curcumin, and bisdemethoxy curcumin (Chatterjee 1999)
Similarly, scientists have observed negligible or no effects on grape pomace, artichoke, pomegranate and increases in tested anti-oxidants or vitamins in strawberries, grapes, romaine, iceberg lettuce, endive, carrot and kale juice, fresh-cut mangoes, apples, broccoli and blueberries - with beneficial effects often being mediated by UV-A,-B, or -C exposure (cf. Alothman 2009). Tomatoes and peppers, on the other hand, don't mix well with high dose gamma- and UV-C irradiation, on the other hand. While we can thus say that the overall effects of irradiation treatment are often negligible, sometimes positive and in a few instances negative, we cannot make a general statement about whether they will or won't have a practically relevant effect on the health-value of foods - although, I would dare to say that UV-treatments appear to have an edge over gamma- and e-beam irradiation for fruits and veggies, while the latter appear more suited for meats and co.

One thing you shouldn't forget is what you get if you buy non-irradiated foods

It's quite funny, isn't it? The same folks that complain about how pasteurization would ruin milk and how adding preservatives (often citric acid or vitamin C) to foods would turn health- into Frankenfoods will refuse to buy any produce that has been subjected to ionizing radiation. Well, guess what: if you don't want the former, you will have to live with the latter.
Table 2: With the exception of spices, the FDA allows only radiation intensity below the 25kGy that has been observed to trigger sign. changes in the molecular structure of food products to be used (FDA, CFR 179.26(b)); the standards in Europe are even stricter with treatments at intensities >10kGy being prohibited by the European Commission (2015).
As J.F. Diehl points out, "[i]rradiation [can] be used for inhibition of sprouting, disinfestation, destruction of parasites in meat, to delay maturation of fruit and for pasteurization and sterilization" - all processes, where it will replace chemical sprout inhibitors, fumigants and chemical preservatives and/or have "unique advantages e.g. in eradication of non‐spore‐forming pathogens in dry or frozen foods" (Diehl 1992) or sign. less far-reaching effects on food quality compared to heat or pressure treatments.
The WHO regards irradiation one of the best weapons in its fight against foodborne diseases.
To leave the pathogens alone is not an option! Even with today's relatively rigorous anti-pathogen treatments, researchers estimate that only the top 10 pathogens in food sources in the United States are responsible for losses of over $8 billion and, much more importantly, a loss of 36,000 (!) quality-adjusted life years (Batz 2012). Bacteria like listeria, which are usually spread by consuming contaminated non-irradiated raw vegetables, ready-to-eat meals, processed meats, smoked fish or soft cheeses, can result in blood poisoning and meningitis, and brucella, a pathogen that's often found in raw milk and will cause fever, muscle pain, arthritis, chronic fatigue, neurological symptoms, and depression, or cholera, they all can be eradicated with appropriate thermal, chemical or, as discussed here, radiation treatment.

The same goes for other foodborne diseases threatening humanity like Hepatitis A, toxoplasmosis, pork tapeworms (Taenia solium), echinococcus tapeworms, Chinese liver fluke (Clonorchis sinensis) and chemical toxins such as aflatoxins which ar eproduced by mould that grows on grain and can cause liver cancer, one of the most deadly forms of cancer - all pathogens that won't even appear in the CDCs list TOP5 of lethal foodborn illnesses, as their effects are chronic and take years if not decades to kill you. That's unlike Salmonella, Toxoplasma gondii, Listeria mono-cytogenes, Norovirus and Campylobacter spp. which are responsible for 28%, 24%, 19%, 11% and 6% of the ~1350 cases in which Americans die from an acute foodborne disease each year. No wonder that researchers highlight that especially immuno-compromised individuals will largely benefit from an increase in food irradiation (Mohácsi-Farkas 2016).

The radiation levels that are used in practice are also often much lower than the FDA limits. To get rid of molds, bacterium, and yeasts on spices, for example, irradiation doses of only 0.82, 0.86, and 2.69 kGy, respectively, are used. At these intensity levels, the microbial decontamination of spices by ionizing radiation does not seem adversely affect the antioxidant property of the spice - that's at least what studies on cloves, cinnamon, or parsley, in which the irradiation did not affect the volatile composition and other organoleptic properties indicate (Sádecká 2007).
Table 3: Shelf-life of ground beef & poultry products under diff. packaging conditions and e-beam processing (Pillai 2017).
Combined with other techniques to extend the shelf-life, such as modified atmosphere packaging, irradiation can extend the shelf-life of beef cuts to 47 days, fresh ground beef to 34 and skinless boneless chicken to ~30 days (see Table 3). Now, whether that's indeed necessary is certainly debatable. If we want to increase the sustainability of our lifestyle it should yet be obvious that minimizing the amount of produce we throw away because it has not been bought, prepared and/or consumed in time will seem significantly more attractive to many that the vegan demand to stop eating beef and other often similar or even more perishable foods altogether.
Reduction in infection risks from non-O157 Shiga-toxin producing e-Coli contaminated strawberries associated with 1 kGy dose of E-beam processing (Shayanfar 2017) - vitamins (Dionísio 2009), flavanols and also the phenolic acids (Breitfellner 2002a,b) remain largely unaffected if the radiation dose is kept to a minimum.
What should I know? While irradiation will, just like any other food processing technology (including chewing, by the way) affect the nutrient content availability of food products, the process is - assuming that the minimal necessary irradiation level is used - not just safe, it will also have sign. less far-reaching effect on the health effects of foods than thermal processing or the use of chemical anti-bacterial, anti-fungal, and anti-mold agents.

Over the past years, researchers, including those from the influential American Dietetic Association, have repeatedly advocated irridation based on studies showing that it can reduce the risk of e-coli infections from infected strawberries, for example, by a whopping -99.992% - without relevant effects on their vitamin or flavenol content - at high radiation intensities, some of the phenols may be lost, though (Breifellner 2002a,b; Dionisio 2009).

Against that background, it's somewhat surprising that spices (here it's  necessary) and imported products like mango from India, where the technology is used routinely on almost everything that cannot run away, are the only products in the average US American grocery store that have been irradiated. How's that? Well, the two most important reasons start with "r": "regulations" the industry is facing when it comes to the use of food irradiation and "retailers" which are afraid that their uninformed customers won't buy products with the "Radura" label. For you as a now educated customer, the label shouldn't be a reason to pass on any product - in fact, in the case of spices, I'd advise to actually look for those in which the germs have been killed by radiation | Comment!
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  • Batz, Michael B., Sandra Hoffmann, and J. Glenn Morris Jr. "Ranking the disease burden of 14 pathogens in food sources in the United States using attribution data from outbreak investigations and expert elicitation." Journal of food protection 75.7 (2012): 1278-1291.
  • Beaulieu, M., M. Béliveau G. D'Apran, and M. Lacroix. "Dose rate effect of γ irradiation on phenolic compounds, polyphenol oxidase, and browning of mushrooms (Agaricus sports)." Journal of agricultural and food chemistry 47.7 (1999): 2537-2543.
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