gliadin in seven children who had anaphylactic reactions to breads, buns, noodles, macaroni and pizza.
3. Detecting and Measuring Allergens There are several factors that make it difficult to detect and measure food allergens. These include sampling problems and difficulties in quantifying proteins, particularly allergenic proteins, in a wide variety of foods. Further, an allergen may be a minor component of a highly complex, heterogeneous food. The food matrix can sequester allergens, hindering detection, while not significantly affecting allergenicity. It is also difficult to estimate the amount of a food allergen that may be present from the result of an assay that only measures protein, particularly when there is more than one allergenic protein.
The only commercial methods that have been shown to detect food allergens reliably use immunological techniques such as ELISA (Poms et al., 2004; Krska et al., 2003), although non-commercial PCR assays have been described (e.g., Popping et al., 2004). In some cases, these methods were designed to detect representative biomarkers, not necessarily a specific allergenic protein. Many kits contain polyclonal antibodies that detect both non-allergenic and allergenic proteins (e.g., Nogueira et al., 2004). For example, the peanut ELISA assays that have completed Multiple Laboratory Performance Tested validation are designed to detect multiple proteins indicative of the presence of the food (e.g., peanuts), not to detect or quantify specific allergenic proteins (Park et al., 2005). There are no validated detection methods or commercially available kits for most food allergens or allergenic proteins.
The FDA and AOAC investigated the ability of three commercial peanut test kits [BioKits Peanut Testing Kit (Tepnel), Veratox for Peanut Allergens (Neogen Corp.), and RiDASCREEN Peanut (R-Biopharm GmbH)] to accurately measure peanuts in four food matrices (cookies, ice cream, milk chocolate, and breakfast cereal) (Park et al., 2005). The validation study, requiring 60 analyses of test samples at the target level of 5µg peanut/g of food and 60 analyses of “peanut-free” controls, was designed to ensure that the lower 95% confidence limit on the true sensitivity and specificity rates exceeded 90% (Park et al., 2005). The results from this study showed that all the test kits correctly allocated the test samples at the target level. No comparable studies have been completed for any other food allergen.
Scientific practice is to calibrate, standardize, and validate assays and commercial test kits for each food product because minor differences in the matrix change the recovery and detection of specific food proteins. Standardization requires the preparation of samples identical to the test sample and containing known amounts of a specific food allergen. Nevertheless, because different antibody-based assays recognize different protein epitopes, variable results may be obtained using different test systems. This variability was evident in results obtained in the Food Analysis Performance Assessment Scheme (FAPAS®) supervised proficiency studies of wheat (Central Science Laboratory, 2003a; Central Science Laboratory, 2004b), peanut (Central Science Laboratory, 2003b),
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