Chapter 29
Improvement of Immunoassays for the Detection of Food Allergens Carmen D. Westphal
Downloaded by YORK UNIV on July 2, 2012 | http://pubs.acs.org Publication Date: October 20, 2008 | doi: 10.1021/bk-2008-1001.ch029
Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, Laurel, MD 20708
The development of immunoassays for the detection of food allergens is a challenging task because the target is usually a complex mixture of allergenic and non-allergenic proteins of diverse structural and chemical properties. Moreover, the detection of these proteins might be affected differently by food processing. Consequently, it is difficult to predict which proteins are actually being detected by the immunoassay. Indeed, the protein profile in the sample extract might not be fully comparable to that of the calibrators, which brings up the question of accuracy in a quantitative assay. A better characterization of extracts from allergenic foods is needed in order to standardize, optimize, and validate the detection methodology. This chapter will highlight some of the proteomic tools to optimize the detection of food allergens.
In the US, the Food Allergen Labeling and Consumer Protection Act (FALCPA) requires all products containing major allergenic foods (milk, egg, soy bean, wheat, peanut, tree nuts, crustaceans, and fish and their products) to be indicated in the ingredient list. Analytical methods are needed to detect the inadvertent presence of allergens in processed foods. There are commercial immunoassays available for only some of the eight major allergenic foods, none of which have been formally validated. Only some peanut kits have undergone a performance evaluation under the AOAC Research Institute program (1). Validation is needed to ensure the specificity, accuracy, and precision of the kits and to guarantee reproducible results. All these elements provide a solid basis 448
U.S. government work. Published 2008 American Chemical Society.
In Food Contaminants; Siantar, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.
449 for making labeling decisions. Commercial peanut kits are quantitative tests but they differ in their ability to provide the same result for the same sample. In our research we have evaluated, at the molecular level, some of the factors responsible for this variation and the possible options to help reduce inherent uncertainty of these kits. The understanding of these factors is necessary to improve and standardized detection methods and they should be considered in the planning of the validation process.
Downloaded by YORK UNIV on July 2, 2012 | http://pubs.acs.org Publication Date: October 20, 2008 | doi: 10.1021/bk-2008-1001.ch029
Understanding the Target The most important factor in the development of any detection assay is the understanding of the nature of the target. Every compound has specific properties determined by its physical and chemical characteristics, which govern how the different steps in the analysis process are designed and optimized. Proteins are a heterogeneous group of large molecules that have very different roles in nature. The activity of proteins is determined by their 3-dimensional structure. Food allergens are proteins, but not all the proteins are allergenic. It still remains uncertain why only some proteins are allergens and why sensitive individuals are allergic to some but not all of them.
Food Allergens as Targets Food allergens as targets are not like any other biological markers. Biological targets like the prostate specific antigen (PSA), used as a marker for prostate cancer, are always detected as intact molecules. However, an additional and very important factor has to be considered in the development of detection assays for food allergens, and that is food processing. Food is a defined mixture of ingredients that can undergo different chemical (acidification, fermentation), physical (heating, extrusion, microwaving, high pressure, irradiation), or enzymatic treatments. During the production of foods the different food components are modified or they interact with each other resulting in a final product characterized by its specific texture, flavor, color, and moisture, among other properties. The processing of food may cause the irreversible modification of some individual ingredients, including proteins (2). Like any other component food allergens are also affected by food processing (3, 4) and this may have an important impact in the analytical process. Food allergens can form chemical cross-links to other food components, such as sugars in the so-called Maillard reaction (5,
