EurFoodResTechnol2000)211:360±365  Springer-Verlag 2000 Original paper T. Holzhauser ´ A. Wangorsch ´ S. Vieths Polymerase chain reaction PCR) for detection of potentially allergenic hazelnut residues in complex food matrixes Received: 9 November 1999 / Revised version: 9 December 1999 Abstract A new method for the specific and sensitive detection of potentially allergenic hazelnut Corylus avellana) residues in complex food matrixes has been developed applying the polymerase chain reaction PCR) with ªhot startº and ªtime-releaseº features. By amplifying a 182 bp- fragment of the coding deoxy- ribonucleic acid cDNA) of Cor a 1, the major hazel- nut allergen, detection of even 0.001% of hazelnut in commercial food products could be demonstrated. Results were confirmed by our previously described sandwich-type enzyme-linked immunosorbent assay ELISA) that quantifies potentially allergenic hazelnut protein at trace levels. Key words Hazelnut ´ Hidden allergens ´ PCR ´ ELISA Introduction In central and northern areas of Europe, allergy to hazelnut is very common in patients allergic to tree pollen, especially birch pollen [1±3]. Ingestion of the offending food may lead to severe allergic reactions [4±7] that can even be life-threatening. Problems may thus arise from an accidental intake of hidden allergens, because the presence of the offending food may not always be discernible by the allergic con- sumer for various reasons such as mislabeling or unknown cross-contamination of products. For better protection of consumers suitable methods are required for specific and sensitive detection of hidden allergens. Non-declared hazelnut residues have already been detected by rocket immunoelectrophoresis [8], radio- allergosorbent test [9] and enzyme-linked immunosor- bent assay ELISA) [10, 11]. In a previous study, 12 of 28 commercial food products without labeling or declaration of hazelnut components contained between 0.002 ppm and 421 ppm of hazelnut protein corresponding to some 0.002±0.5% of hazelnut [10]. Malmheden Yman et al. [5] showed that ingestion of only one piece of chocolate containing 0.2% of unde- clared hazelnut corresponding to about 6 mg of hazelnut protein) caused a severe allergic reaction in a sensitive individual. For routine analysis of hazelnut residues in complex food matrixes, two sandwich-type ELISA applications have already been published [10, 11]. Even though the immunochemical detection of the protein fraction that elicits the allergic reaction allows a good overall risk assessment of potentially allergenic foods, immunochemical techniques based on polyclonal antisera have some restrictions concerning availability of high quality antisera with good batch- to-batch consistency. The polymerase chain reaction PCR) may thus serve as an independent alternative if the detection of DNA correlates with the presence of potentially allergenic protein in the food: Allmann et al. published a PCR application for specific wheat detection in non-wheat food products with special regard to wheat gluten intolerance coeliac disease) as a possible alternative to an existing immunoenzymatic gliadin detection kit [12]. In this paper we describe the specific and sensitive detection of hazelnut by PCR in comparison to our previously described hazel- nut-specific ELISA. Materials and methods Hazelnut samples and food products The hazelnut samples, food products and model foods investi- gated were described elsewhere in detail [10]. General notes on chemicals, reagents and materials All chemicals and reagents used were of ªmolecular biologyº or at least of ªanalyticalº grade. All materials used, from sample T. Holzhauser ´ A. Wangorsch ´ S. Vieths  ) ) Paul-Ehrlich-Institut, Department of Allergology, 63225 Langen, Germany e-mail: viest@pei.de