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The EC-JRC manuscript entitled "Interlaboratory validation of thirteen qPCR methods to quantify adulterants in culinary spices and herbs”, has recently been published (open access) in the journal of European Food Research and Technology.

The paper describes the results of a recent inter-laboratory trial using 13 qPCR assays for the detection of  significant adulterants in  paprika/chili, turmeric, saffron, cumin, oregano and black pepper.  For paprika, adulterants tested were maize seed, tomato, and sunflower seed.  For saffron, adulterants were safflower and Mexican marigold.  For cumin, carroway seed.  For turmeric, maize seed, rice seed, oat seed and bell pepper.  For oregano, goose-foot leaf.  For black pepper, rice seed.

The thirteen qPCR methods had already passed in-house validation criteria (from an original pool of 30 methods – results previously published).  This study was an inter-laboratory trial involving 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.

The authors report that, 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%.

They conclude that the thirteen qPCR methods are therefore fully validated and may be included in international standards for deployment in official control laboratories.

Photo by Tamanna Rumee on Unsplash

Energy-Dispersive X-Ray Fluorescence (EDXRF) is a cheap non-destructive technique to measure metal and mineral content, typically operated as a laboratory benchtop method.

In this study (open access), researchers at the European Commission Joint Research Centre used market samples of oregano that had been previously tested under the EU co-ordinated official control plan to investigate whether EDXRF could be used as a screening technique.  This was a serendipitous extension of the use of EDXRF for checking compliance with EU limits for copper contamination.  After a relatively simple sample preparation, they measured a panel of 36 metals and minerals.

They found that, at it simplest level, the ratio of copper-to-zinc was a good indicator of adulteration with olive leaves without any need for modelling statistics.  Once multivariate statistics were used, samples could also be classified by geographic origin.  This classification required 2-stage modelling (SIMCA then PLS-DA) to achieve full potential, and then was limited because the reference dataset was not sufficiently comprehensive in terms of countries of origin.

The researchers concluded that their work demonstrates that EDXRF is a suitable screening method to detect oregano adulteration with other species, and to authenticate the geographical origin of the product. The method is clean, cheap and has a high sample throughput because it does not require sample digestion. For those reasons, the approach is ideal to be used by control laboratories.

SIMCA allowed the authentication of the geographical origin of oregano. The performance of the authentication could be improved with a combination of SIMCA with PLS-DA that provides sensitivities and specificities higher than 90 %. However, a database well populated with results obtained with samples coming from all the main producing countries, would be needed.

A recent survey undertaken by professor Chris Elliott on behalf of Which? magazine has found that a quarter of 78 samples labelled as oregano contained other ingredients, in some cases forming up to 70% of the product.

Read more at Which? >>

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