Interlaboratory validation of a droplet digital PCR method for quantifying common wheat (Triticum aestivum) in spelt (Triticum spelta) products

Spelt products are popular with consumers achieving higher market prizes, making them susceptible to food adulteration with less valuable cereals. To facilitate product control, a recently developed duplex droplet digital PCR method enables the detection and quantification of common wheat (Triticum aestivum) contaminations in food products made from spelt (Triticum spelta). The duplex droplet digital PCR assay targets the γ-gliadin gene and the Q-locus of both subspecies. In this study, the method was validated in an interlaboratory ring trial involving 11 participating laboratories. Test materials containing defined proportions of spelt and common wheat were prepared and tested. The ring trial procedure included DNA extraction of the test samples and determination of subspecies proportions using droplet digital PCR. Results from the ring trial confirmed the method's capability for specific detection and quantification of common wheat in spelt, with acceptable relative measurement uncertainties, and without requiring reference material for calibration. To our knowledge, this is the first interlaboratory validation of a digital PCR method for species differentiation in food.