DNA Comet Assay––a rapid screening method for detection of irradiated cereals and tree nuts

Whole grains of some important cereals (wheat, buckwheat, maize, millet and oat) and some whole tree nuts (almonds, Brazil nuts, cashew nuts, peanuts, walnuts, hazelnuts, pistachio nuts and pine nuts) have been investigated for the identification of radiation treatment using microgel electrophoresis of single cells. This DNA Comet Assay is proposed as a rapid screening method for detection of irradiated foods, but is not radiation specific. Cereals and nuts were exposed to radiation doses of 0.5, 1 and 3 or 5 kGy covering the range for insect/pest disinfestation or for microbial control. After electrophoresis, irradiated cells from buckwheat, maize, millet and oat, and also from almonds, peanuts, walnuts and hazelnuts showed comets indicating stretching of fragmented DNA towards the anode. The size and shape of the comets were dose dependent. Non-irradiated samples of all cereals showed intact cells/nuclei in form of round stains or with short faint tails except for wheat, which showed only comets also in non-irradiated samples. For nuts like Brazil, cashew and pistachio nuts, suitable DNA material could not be extracted. In case of pine nuts, very few round intact cells were observed along with a majority of comets, making the screening difficult. Thus comet assay can be successfully used as a screening method for detection of radiation treatment of several cereals and nuts, however, the assay was not satisfactory for wheat and for Brazil nuts, cashew nuts, and pistachio nuts.