Application of droplet digital PCR for the detection of fish DNA in food products

Fish is one of the most common causes of food allergy. The global prevalence of fish allergy has increased over the years as a result of the increased fish consumption. In allergic individuals even small amounts of allergen can trigger a life-threatening allergic reaction. Correct food allergen labelling plays a crucial role in consumers protection. Food business operators are required to verify compliance with labelling requirements. In order to do so, they need reliable, specific and sensitive methods for the detection of fish in food products. The present study evaluated the use of a droplet digital PCR assay for the identification of fish allergen in a variety processed foods. The method was developed targeting the ribosomal 18S rRNA gene. The specificity, the limit of detection (LOD) and of quantification (LOQ), dynamic range and selectivity were evaluated. The LOD and LOQ of ddPCR were 0.08 pg/μL and 0.31 pg/μL, respectively. Following optimization and validation of the method, the digital droplet PCR was tested on 37 prepackaged food samples placed on the market. Samples comprised a variety of composite foods, including both animal and plant- origin ingredients. The presence of fish was identified in the ingredient list of some samples, while in others, it was indicated as traces or not listed at all. The presence of fish DNA was detected in 16 out of 18 labeled fish-containing samples (88.9 %), while it was never detected in foods where fish was not declared on the label. The results of this study demonstrate the strong potential of droplet digital PCR (ddPCR) as a highly sensitive and specific method for detecting fish allergens in complex food matrices.