|Definition of food allergy
Adverse reactions to food, i.e. food hypersensitivity, are divided into immune-mediated and non-immune mediated reactions. Immune-mediated reactions to food are mediated either by IgE antibodies or other immunological pathways. Food intolerances comprise non-immune-mediated responses that are dependent on enzyme deficiencies, pharmacological reactions, or, as is true in the majority of cases, arise by unknown mechanisms (EFSA, 2004).Risk assessment in food allergy
There is high variability in sensitivity between different sensitised individuals with respect to the dose of allergens required to trigger an adverse effect. The assessment of no observed adverse effect levels (NOAEL) is therefore impracticable, impairing risk evaluation. Therefore, threshold levels that would protect 99 % of the allergic consumers and produce only mild symptoms in the most sensitive are under consideration.It is important to understand the mechanisms of food allergy in order to assess risk, to prevent and treat food allergy. Through cooperation with clinical physicians in Norway and Spain we have the possibility to align our analytical research on food allergens with patient data. Additionally, we have a successful long-term cooperation with the Norwegian Institute of Public Health, especially in work concerning the Norwegian National Register and Reporting System for Severe Allergic Reactions to Food (“Matallergiregisteret”)
Food allergens characteristics
Food contains an enormous variety of proteins, but only a small fraction owns allergenicity, and these can be either abundant or minor ingredients. The known allergens belong predominantly to a limited number of protein families with biological functions such as storage, hydrolysis, metal- and lipid-binding, as well as cytoskeleton association. Molecular masses range generally from 10 to 70 kDa. Many allergens occur in multiple isoallergenic forms showing 67% or more identity in amino acid sequence. Post-translational modifications and glycosylations contribute further to allergen diversity. Allergenicity of foods can originate either from a variety of different proteins with comparable allergenic capacity or from one dominating allergen. Leguminous plants like peanut, soybean and lupin are typical examples for foods containing a considerable number of potent allergenic proteins. In contrast, crustacean, fish, and molluscan allergy are predominantly caused by allergic reactions against one prevailing muscle protein of the respective animal. Food allergens are characterized by their high stability towards heat, low pH and enzyme digestion, and the ability to usually survive food processing. Many detection methods are therefore based on the determination of one or several of the allergenic proteins in food.
Analytical methods for food allergens
The implementation and control of product labelling guidelines depends on the availability of reliable and sensitive analytical methods that specifically identify allergenic proteins in complex mixtures. Various techniques have been developed detecting qualitatively or quantitatively either the allergenic protein itself or a typical marker that signifies its presence.Protein-based detection methods usually are based on immunochemical allergen detection, involving either IgE from patient sera or polyclonal and monoclonal IgG-antibodies generated by animal immunization. Polymerase chain reaction (PCR) is a commonly used indirect technique that detects DNA as a representative for the allergen. Furthermore, analysis by mass spectrometry (MS) for the identification, characterization and determination of food allergens has become more important in the last years.
Important food allergens
Among the identified allergens, only a few can be considered major allergens, occurring in common foods and affecting a large portion of the allergenic population. Different dietary habits of the consumers have brought about national distinctions in the prevalence of specific food allergies.
In the U.S. eight foods including crustaceans, egg, fish, milk, nuts, peanut, soybean, and wheat have been found to cause the majority of food allergenic reactions. Additionally, sesame is of importance in Australia, New Zealand, Canada, and the European Union (EU). Furthermore, Canada and the EU consider mustard as important allergen, and finally, the EU has extended the list with celery, lupin and molluscs to in total 13 foodstuffs and products thereof. In Japan and Korea, allergy to buckwheat is of considerable importance aside from the eight major allergens.