Food allergens: an analytical challenge for the agri-food chain

Food allergy, an abnormal immunological response due to sensitization to food proteins, has become an important food safety problem, especially in industrialized countries. Together with hen’s egg, fish, crustacean, peanut, and wheat, tree nuts such as hazelnut (Corylus avellana), soybean (Glycine max) and cow’s milk are associated with severe allergic reactions. Hazelnut, soybean and cow’s milk proteins are extensively used as food ingredients. However, their undeclared presence in foods, due to for example an unintentional contamination during food production, can pose a serious threat for the allergic consumer. Therefore, accurate and reliable methods to assess the potential presence of allergens in raw materials and the end products are essential. Currently ELISAs, based on the molecular recognition of specific proteins by antibodies, are the preferred methods to assess levels of allergen contamination, both by the food industry and enforcement agencies. During food processing however, proteins are prone to a variety of molecular modifications. It was observed that these modifications affected dramatically the detection of hazelnut and soybean allergens using commercial ELISAs. Remarkably however, it was observed that the loss in detectability as a result of protein glycation and thermal processing did not result in a loss of allergenicity of the hazelnut proteins for example, especially for patients with severe allergic reactions. Based on these results, it can be concluded that, currently no reliable commercial analytical methods are available which allow the (quantitative) detection of the considered allergens. Therefore, new and more robust analytical approaches were evaluated. Using MALDI-TOF-MS, peptides derived from hazelnut, soybean and whey proteins could be identified which remained stable throughout a variety of chemical reactions occurring during food processing. As a consequence, these stable peptides can be used as indicators for the presence of the considered allergenic proteins. This hypothesis was successfully evaluated by developing antibodies toward a very stable hazelnut allergen - Cor a 9, which were used in a robust sandwich ELISA. The robustness of ELISA could be also improved by developing antibodies towards a mixture of chemically modified proteins. However, food processing had a severe impact on the recovery of the target allergens from foods due to affected extractability. This indicated that methods to improve the extractability of the target allergens should be found and tested for their applicability in ELISA. Therefore, to be able to protect the allergic consumers, food industry needs to make further efforts to avoid contamination with allergens