Differentiation of important and closely related cereal plant species (Poaceae) in food by hybridization to an oligonucleotide array

We report the development of an oligonucleotide microarray for the simultaneous detection of six important cereal food plant species from the Poaceae based on the chloroplast trnL intron sequence. We used universal primers to amplify the trnL intron from wheat, rye, barley, oat, rice, and maize, followed by a cyclic labeling of oligonucleotides probes and subsequent hybridization to an oligonucleotide microarray. In single taxon analyses, positive signals were produced with a high signal-to-noise ratio. The assay also enabled the analysis of mixed samples. The results obtained for real food samples were in agreement with the ingredient labels, but positive results for grains not declared on the ingredients list were observed in three out of 10 samples, which indicates that the final products and/or the declared ingredients were probably botanically impure or contaminated. The combination of the sensitivity of a universal polymerase chain reaction with the specificity of the labeling reaction allows this protocol to be applied in routine analyses of food samples, as demonstrated by successful analysis of processed composite food products.