Interlaboratory validation of thirteen qPCR methods to quantify adulterants in culinary spices and herbs

Culinary spices and herbs are vulnerable to fraudulent practices adulterating or substituting their authentic composition. Recently, we conducted an in-house validation of thirty real-time quantitative polymerase chain reaction (qPCR) methods aiming at detecting and quantifying the top five adulterants of six commonly consumed spices and herbs: paprika/chilli, turmeric, saffron, cumin, oregano and black pepper. Each of the thirteen qPCR methods meeting all the in-house validation criteria have been further tested in an interlaboratory trial including fifteen European laboratories. For each method the participants received DNA templates of binary mixtures for five standard samples together with five test samples of unknown adulterant concentration. Interlaboratory validation parameters included repeatability, reproducibility and trueness. Measurement uncertainties, limits of detection and limits of quantification were also determined. After data examination and outlier removal, relative repeatability standard deviation ranged from 4% to 25%, relative reproducibility standard deviation ranged from 6% to 25% and trueness bias ranged from − 11% to 27%. The thirteen qPCR methods are therefore fully validated and may be included in international standards for deployment in official control laboratories.