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Handling major hypersensitivity reactions (e.g. celiac disease) triggered by proteins of wheat and other cereals is a challenging task for healthcare systems, legislative forces and the related fields of food analysis as well. In spite of the fact that there are available official threshold levels for labelling the absence of gluten, which is considered to be the toxic protein fraction of wheat, barley and rye, validation of the analytical methodology supporting regulatory requirements is currently problematic. The main limiting factors of method validation are the lack of reference methods and reference materials. The objective of this study was to provide a solution to this problem. An incurred reference material in a model food matrix was developed and studied by commercially available ELISA test kits as a part of the activity of the Food Allergen Working Group within the FP6 funded EU project MoniQA. After successful completion of the reference material development process, the incurred material was used as a basis of a comparative study examining the performance and applicability of seven commercially available ELISA kits designed for quantification of gluten/gliadin. In certain cases the obtained data showed discrepancies from the expected gliadin content that may carry both a food safety and an economic relevance. The evaluation of the effects of heat treatment on the analytical results is also presented, highlighting the fact that the food processing steps may have a considerable impact on the analytical data, thus should be carefully handled during method development and validation.

Celiac disease and wheat allergy are the most common adverse reactions triggered by cereal proteins, mainly gluten, which is one of the 14 allergenic food ingredients that must be labeled on food products in the European Union (EU). To meet the requirements of this regulation, reliable analytical methodology for proper quantification of gluten is necessary. However, validation of presently used methods (ELISA and lateral flow device) is limited partly due to the lack of reference methods and incurred reference materials. To solve this problem, the goal of our work was to develop an incurred reference material for the quantification of gluten under the auspices of EU-FP6 funded Network of Excellence MoniQA. During this work, we produced a processed model product (cookie) containing gliadin (major allergenic fraction of gluten) in a defined amount. This paper addresses the development process of this material together with the associated problems (insufficient homogeneity and low recovery) and their solutions. As a result, an incurred food matrix was produced on a laboratory-scale with a potential use as a reference material. The model product was tested by an ELISA method followed by a comparative study of commercially available ELISA kits to investigate the applicability of the product. Preliminary results of this study are also presented.

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The use of pure oats (oats cultivated with special care to avoid gluten contamination from wheat, rye, and barley) in the gluten-free diet (GFD) represents important nutritional benefits for the celiac consumer. However, emerging evidence suggests that some oat cultivars may contain wheat gliadin analog polypeptides. Consequently, it is necessary to screen oats in terms of protein and epitope composition to be able to select safe varieties for gluten-free applications. The overall aim of our study is to investigate the variability of oat protein composition directly related to health-related and techno-functional properties. Elements of an oat sample population representing 162 cultivated varieties from 20 countries and the protein composition of resulting samples have been characterized. Size distribution of the total protein extracts has been analyzed by size exclusion-high performance liquid chromatography (SE-HPLC) while the 70% ethanol-extracted proteins were analyzed by RP-HPLC. Protein extracts separated into three main groups of fractions on the SE-HPLC column: polymeric proteins, avenins (both containing three subgroups based on their size), and soluble proteins, representing respectively 68.79–86.60, 8.86–27.72, and 2.89–11.85% of the total protein content. The ratio of polymeric to monomeric proteins varied between 1.37 and 3.73. Seventy-six reversed phase-HPLC-separated peaks have been differentiated from the ethanol extractable proteins of the entire population. Their distribution among the cultivars varied significantly, 6–23 peaks per cultivar. The number of appearances of peaks also showed large variation: one peak has been found in 107 samples, while 15 peaks have been identified, which appeared in less than five cultivars. An estimation method for ranking the avenin-epitope content of the samples has been developed by using MS spectrometric data of collected RP-HPLC peaks and bioinformatics methods. Using ELISA methodology with the R5 antibody, a high number of the investigated samples were found to be contaminated with wheat, barley, or rye.

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In special dietary products for people intolerant to gluten, gluten content is not supposed to exceed the regulatory thresholds. Enzyme-linked immunosorbent assays (ELISAs) are routinely used to quantitate gluten in these products. They measure gliadin/gluten with high specifi city and sensitivity, but they have some limitations. Quantitative and qualitative variability of the target proteins among wheat cultivars is a factor that may cause inaccurate results. One of the aims of this work was to characterize the protein composition of fi ve wheat cultivars grown in multiple harvest years and their blends by reversed-phase high-performance liquid chromatography (RP-HPLC). The gliadin/gluten content of these wheat fl ours was also analysed with two commercial ELISA kits. The effect of differences in protein profi les between the fl ours from an individual cultivar and the blend of fi ve cultivars, harvest years, as well as processing procedures (dough forming and baking) on the results of two ELISA kits was investigated and their relative magnitude was determined. Among the factors investigated, the differences between fl ours had the greatest impact on gliadin recoveries.Keywords: wheat fl our, protein composition, gluten-free, gliadin/gluten, incurred matrix, ELISAThe ingestion of food from gluten-containing grains can trigger a number of harmful reactions in susceptible individuals, e.g. celiac disease, wheat allergy, and non-celiac gluten sensitivity. Gluten (especially its prolamin fraction) from wheat, rye, and barley is the precipitating factor for celiac disease . Patients must eliminate these grains from their diet, because currently this is the only effective strategy to avoid the symptoms (SABATINO et al., 2013). Two thresholds are defi ned: the terms 'gluten-free' and 'very low gluten' mean that the gluten content in these products is below 20 and 100 mg kg -1, respectively (COMMISSION OF THE EUROPEAN COMMUNITIES, 2009). Reliable analytical methods are needed to assess the gluten content of these products and to enforce regulations. Currently, immunochemical assays (enzyme-linked immunosorbent assays (ELISAs) and lateral fl ow devices (LFDs)) are the preferred methods for determining such low amounts of protein. However, gluten quantitation with ELISA is accompanied by numerous problems, because gluten is a complex mixture of heterogeneous proteins with different solubility, composition, and immunoreactivity (DIAZ- .Most commercial gluten immunoassays are based on determining prolamins, which are soluble in aqueous alcohols (SCHERF & POMS, 2016). Although the primary structure of prolamins appears to be relatively stable, food processing might induce post-translational * To whom correspondence should be addressed. Phone: +36-1-463-1419; fax: +36-1-463-3855; e-mail: tomoskozi@mail.bme.huThis is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 License, which permits unrestricted use, distribution, and reproduction in any medium for non-commercial purposes, provid...