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The fate of alkylcyclobutanones, which are produced in irradiated foods, has been studied in the rat by researchers in the US in an attempt to allay public concerns regarding the use of this food safety technology. Food safety is a major concern for producers and consumers alike but one area that splits them down the middle is the irradiation of food. Although it has been studied for several decades now and many regard it as acceptable, there is a sizeable and vociferous public minority against it, while government organisations are at great pains to point out that it is "safe." Food is irradiated for several reasons - to destroy bacteria that can cause food poisoning, to delay spoilage in perishable foods, to prevent vegetables from sprouting and to delay ripening of fruits. The permitted categories vary from country to country. For instance, in the UK, the only irradiated foods licensed to be sold are herbs, spices and seasonings whereas, in the US, fruits, poultry and beef are also being treated this way. In both countries, a variety of foods have been granted approval for irradiation, including meats and fish, but take-up is low at this stage. The greatest barriers to expansion of this technology are cost and public opinion. The irradiation facilities utilise gamma rays (from cobalt-60 or caesium-137), electrons or X-rays, so incur high set up and running costs. But the loud and persistent voice of the anti-irradiation lobby cannot be ignored, although not all of their arguments are reasoned, employing such evocative terms as nuked food. In fact, irradiated food does not become radioactive. The main rational claims of the campaigners include the loss of nutrients with potential long-term health damage, although many known methods of food storage can lower the nutrient and vitamin content. One other major concern is the formation of by-products in the food following irradiation, particularly a group of compounds called the alkylcyclobutanones (ACBs). Scientists have known for some time that irradiation converts the major fatty acids present in foods (palmitic, stearic, oleic and linoleic acid) into ACBs. They have not been found in processed or cooked foods, so are actually used as a biomarker of irradiation exposure, their concentration increasing with the dose. However, their toxicity remains a high degree of uncertainty, with conflicting results from research. Some studies have shown that ACBs are genotoxins and may promote cancer, whereas other studies investigating mutagenicity and chromosomal damage have found no adverse effects. Until the metabolism of ACBs is known, it will be difficult to establish their safety (or otherwise), so Scott Smith and Priyadarshini Gadgil from Kansas State University have undertaken such a study in rats. In theory, ACBs or their metabolites could have toxic effects, so it is crucial to know the full metabolic pathway. The researchers investigated 2-dodecylcyclobutanone (2-DCB) which is formed in irradiated foods from palmitic acid. Corn oil containing 2-DCB was given to six rats over five days and their urine and faeces were collected for analysis, as well as adipose tissue at the end of the experiment. All three were extracted for analysis by gas chromatography/mass spectrometry (GC/MS). The presence of 2-DCB was confirmed by the ratios of the ions at m/z 98, 112 and 207 in its mass spectrum and its concentration was determined from a standard calibration curve. The total amount of unchanged 2-DCB excreted in the faeces and stored in the tissue was low, averaging from 3-11% and 0.33%, respectively of the total dose. This points to two conclusions - that most of the 2-DCB is metabolised and excreted, or it is stored in other types of tissue. The researchers looked for potential metabolites in urine, derivatising with a trimethylsilylating reagent to convert any hydroxy or carboxylic acid metabolites so that they are detectable by GC/MS. In addition, urine was hydrolysed with a beta-glucuronidase enzyme to release any metabolites from their conjugated forms. However, they were surprised to find that no metabolites of 2-DCB were detected. The team reasoned that any metabolites formed were metabolised quickly, possibly by opening the cyclobutane ring then following a similar metabolic pathway to that of palmitic acid, the end product being carbon dioxide. This would explain the absence of detectable metabolites. "We were looking to see if 2-DCB was stored somewhere in the body and that is not the case," Smith told spectroscopyNOW.com. "A very small amount is absorbed, but it appears most is metabolized, which is good and doesn't suggest any toxicity." The team also point out that palmitic acid, the precursor of 2-DCB, and other fatty acids themselves induce oxidative DNA damage, cause cell membrane damage and chromosome fragmentation. Comparing the large amount of palmitic acid in a single hamburger with the total estimated intake of 2-DCB, they conclude that "it is difficult to conceive that consumption of irradiated foods containing 2-DCB will significantly increase the risk to human health." Nevertheless, this conclusion should be supported by more research into the metabolism and toxicology of ACBs, so that their fate in the body can be confirmed and consumers will have accurate information from which to draw conclusions on the safety of irradiated foods. Related links:
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Irradiation of food is designed to protect you from bacteria |
