Comparison of real-time PCR methods for quantification of European hake (Merluccius merluccius) in processed food samples

Identification and semi-quantification of Atlantic salmon in processed and mixed seafood products using Droplet Digital PCR (ddPCR)

Fishery products are often subject to substitution fraud, which is hard to trace due to a lack of morphologic traits when processed, gutted, or decapitated. Traditional molecular methods (DNA barcoding) fail to identify products containing multiple species and cannot estimate original weight percentages. As a proof of concept, an Atlantic salmon (Salmo salar) specific ddPCR assay was designed to authenticate mixed food products. The method proved to be specific and able to accurately quantify S. salar when using DNA extracts, even in the presence of DNA from closely related salmon species. The ddPCR estimates correlated well with the percentage of S. salar in artificially assembled tissue mixtures. The effect of common salmon processing techniques (freezing, smoking, poaching with a "Bellevue" recipe and marinating with a 'Gravad lax' recipe) on the ddPCR output was investigated and freezing and marinating appeared to lower the copies detected by the ddPCR. Finally, the assay was applied to 46 retail products containing Atlantic or Pacific salmon, and no indications of substitution fraud were detected. The method allows for a semi-quantitative evaluation of the S. salar content in processed food products and can rapidly screen Atlantic salmon products and flag potentially tampered samples for further investigation.

Comparison of Real-Time PCR Quantification Methods in the Identification of Poultry Species in Meat Products

Poultry meat is consumed worldwide and is prone to food fraud because of large price differences among meat from different poultry species. Precise and sensitive analytical methods are necessary to control poultry meat products. We chose species-specific sequences of the cytochrome b gene to develop two multiplex real-time polymerase chain reaction (real-time PCR) systems: one for chicken (Gallus gallus), guinea fowl (Numida meleagris), and pheasant (Phasianus colchicus), and one for quail (Coturnix japonica) and turkey (Meleagris gallopavo). For each species, added meat could be detected down to 0.5 % w/w. No cross reactions were seen. For these two real-time PCR systems, we applied three different quantification methods: (A) with relative standard curves, (B) with matrix-specific multiplication factors, and (C) with an internal DNA reference sequence to normalize and to control inhibition. All three quantification methods had reasonable recovery rates from 43% to 173%. Method B had more accepted recovery rates, i.e., in the range 70-130%, namely 83% compared to 75% for method A or C.