Detection of wheat contamination in oats by polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA)

Abstract

It is well established that the consumption of wheat prolamins causes the characteristic symptoms of coeliac disease (CD) in subjects who are predisposed to it. There is currently much discussion about the role of oats in the pathogenesis of CD. Evidently, it is important that oats used for clinical studies are not contaminated with wheat. In this study, 38 oat samples were investigated by polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA): 30 samples consisted of flakes or grains and 8 probes were industrially processed oat diets. Wheat prolamin (gliadin) detection by ELISA showed that 16 of these samples contained less than the detection limit of 0.2 mg gliadin/100 g dry weight; 21 samples contained less than 2.8 mg gliadin/100 g dry weight and 1 sample reached 38 mg gliadin/100 g dry weight, clearly exceeding the allowed Swiss limit of 10 mg gliadin/100 g dry weight for gluten-free products. Spiking experiments showed that the wheat PCR system is about ten times more sensitive than the ELISA system, provided that the isolated DNA is fully amplifiable. Thus, wheat DNA could be detected by the wheat PCR system in ten samples with gliadin contents below the detection limit of the ELISA system used. Applying a eukaryote-specific 18S-PCR system the presence of amplifiable DNA was verified. Only two of eight samples of industrially processed oat products contained amplifiable DNA, the other six samples had no detectable DNA left. One sample was wheat-PCR positive. However, all eight samples contained detectable amounts of gliadin in the ELISA.