Determination of the allergenicity of various hazelnut products by immunoblotting and enzyme allergosorbent test inhibition

Abstract

Although allergic reactions to hazelnuts are common especially in Europe, there are only a few investigations with regard to the influence of processing on the IgE-binding potency of hazelnut proteins. In this study the allergenicity of different hazelnut products, such as chocolate, nougat products, croquant or cookies, was examined by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE), immunoblotting and enzyme allergosorbent test (EAST) inhibition experiments using sera of 17 hazelnut-allergic individuals. In only a few cases did the immunoblotting experiments yield positive results as regards the allergenicity of the investigated products. By means of EAST inhibition a residual IgE-binding potency could be detected in almost all of the product extracts. Therefore hazelnuts are a potential hazard to allergic people even as an ingredient of processed foods.

Introduction

The immediate-type allergic reaction to foodstuffs is a common disease the prevalence of which has been estimated at 1–3% among the adult population and up to 5–8% among the pediatric population [1]. Especially in Europe hazelnuts are considered a widespread cause of food allergies among both children [2] and adults [3]. Hazelnut allergy is part of the phenomenon of pollen-associated food allergies, which are the most common food-induced allergic reactions in Europe [4], [5]. Cross-reactivities often occur among the major allergens of birch pollen and the proteins of, for instance, hazelnut, apple, carrot, potato and kiwi [6], [7], [8], [9], [10], [11]. Fifty to 93% of patients with birch pollinosis also suffer from hazelnut and/or apple allergy [12]. Cross-reactivities between hazelnut and further tree pollens, such as alder, hazel, hornbeam, oak and mugwort, are documented as well [7], [12], [13], [14], [15], [16]. Various authors have demonstrated the existence of a partial immunological identity between birch pollen and hazelnut proteins [8], [17]. In a further work [18] the existence of two common allergens in hazel pollen and hazelnut has been revealed: a 17-kDa allergen in hazel pollen and an 18-kDa allergen in hazelnut, respectively. An additional 14-kDa allergen has been shown in both hazel pollen and hazelnut, which is considered a profilin and is cross-reactive to the 14-kDa birch pollen profilin. The 18-kDa allergen in hazelnut is considered cross-reactive to the 17-kDa major allergen in birch pollen Bet v 1. Additional IgE-binding proteins in hazelnut have been detected at 37, 40, 46 and 69 kDa.

Although even near-fatal anaphylactic reactions to processed and heated hazelnuts have been described [19], [20], very little is known about the influence of processing on the IgE-binding potency of the allergens [21]. This is hardly comprehensible, because hazelnuts are used as ingredients of many foodstuffs and are marketed in many forms. Besides, in Germany hazelnuts belong to the most important so-called hidden allergens in foodstuffs [22].

Whilst in a previous study we dealt with the influence of different heat treatments and storage on the allergenicity of the IgE-binding proteins in hazelnuts [23], the aim of this study is the investigation of the allergenicity of the wide spectrum of foodstuffs which contain hazelnuts, such as chocolates, nougats and cookies, for example, by means of SDS–PAGE, immunoblotting and enzyme-allergosorbent test (EAST) inhibition.