Markers for irradiated food

Irradiated food can be distinguished from untreated food by the presence of a newly discovered volatile hydrocarbon marker compound.

One of the cleanest and safest methods of preserving food is high-energy ionising radiation treatment that kills many viable microorganisms in meat, seafood, spices and herbs to prolong shelf life and prevent food-borne diseases. It can also be employed to kill or sterilise insects that infest stored foodstuffs such as grains and dried fruits, to retard ripening of vegetables and fruit, and to prevent sprouting of vegetables. The most commonly used radiation source is gamma rays emitted from ⁶⁰Co, although x-rays and electron beams have also been employed.

The commonly recognised advantages of food irradiation are the absence of chemicals, the ability to treat fresh, packaged or frozen foods and the low energy requirements. However, these are counterbalanced by the high capital cost of the radiation plant and public concern over the safety of irradiated food, with the result that very few licences have been issued for irradiation, even though it is authorised in many countries.

To detect irradiated powdered foodstuffs, Korean researchers have compared the volatile compounds present in untreated and gamma ray-treated beef extract powder. Samples were vacuum packed, irradiated with 1-10kGy doses and stored for up to 30 days. Volatiles were extracted by solid-phase microextraction (SPME) or purge-and-trap (P&T) methods and identified by gas chromatography/mass spectrometry.

The extraction methods proved to be complementary: P&T was more efficient for low-molecular-mass and highly volatile compounds; SPME preferentially extracted less volatile species. Out of 61 compounds extracted by SPME and 70 compounds by P&T, only one suitable marker compound for irradiation was detected: 1,3-bis(1,1-dimethylethyl)benzene was absent in untreated food but was produced upon gamma-ray irradiation, its concentration correlating with increasing radiation doses. Other candidate marker compounds did not persist following irradiation, or were also present in untreated food.

The researchers suggest that 1,3-bis(1,1-dimethylethyl)benzene arose from the reaction of methyl radicals, produced by irradiation, with xylene. The findings were consistent with beef extract powders from three commercial food companies.

Steve Down