Sensitive time-resolved fluoroimmunoassay for the detection of hazelnut (Corylus avellana) protein traces in food matrices

Allergy to hazelnut is one of the most prevalent causes of severe food-allergic reactions in Norway, as recorded by The Norwegian National Reporting System and Register of Severe Allergic Reactions to Food. In the majority of the reported cases, there is "hidden", unlabelled hazelnut protein in processed foods like chocolate, cookies and cereal mixtures the eliciting agent. For a food survey study performed to evaluate the labelling practices with regards to hazelnut on behalf of the Norwegian Food Safety Authority, a new sensitive time-resolved fluoroimmunoassay (TR-FIA) for the detection of hazelnut protein traces in food matrices was developed and validated. The unique fluorometric properties of the europium-chelates used improved the signal-to-noise ratio because of low matrix interference and led to an enhanced sensitivity. The limit of detection was 0.1 mg/kg and the limit of quantitation was 0.33 mg/kg hazelnut protein. The recovery ranged from 73% to 123% in cookies and cereals, and from 50 to 77% in chocolate. The intra-assay precision was 7% and the inter-assay precision was 19%. Of 100 randomly chosen retail food products in Norway labelled "may contain hazelnut", 36 contained < 0.2 mg/kg and seven > 10 mg/kg hazelnut protein, demonstrating how differently this precautionary label is used. (c) 2006 Elsevier B.V. All rights reserved.