Objective: Analytical methods for measurements of gluten in the low level range of 20-200 ppm of gluten, as required for gluten-free food, have never been endorsed by the Codex Alimentarius. With the aim of investigating standardized and reliable methods for the detection of gliadin in food with detection limits lower than 200 ppm, as proposed by the Codex Alimentarius, the Working Group on Prolamin Analysis and Toxicity (WGPAT) coordinated a large collaborative study to validate a monoclonal antibody based ELISA, which uses an antibody (R5) against rye secalins.
Methods: Twelve food samples in which gliadin was present in the range of 0-168 ppm were analysed with two different commercially available R5 ELISA tests and a special extraction solvent, based on a reducing and a dissociating agent designed to extract heat denatured proteins. Twenty laboratories participated in this study.
Results: Recovery values ranged from 65 to 110% in general. The repeatability (RSDr) and reproducibility (RSDR) figures ranged between 13 and 25, resp. 23 and 47 for one test, and between 11 and 22, resp. 25 and 33 for the other.
Conclusion: Both assays are comparable and robust. The repeatability and reproducibility data are in a range that is acceptable for ELISAs. Kits from both suppliers fulfilled performance criteria of regular ELISA methods, and it is shown that both ELISA kits guarantee a sensitivity of 1.5 ppm gliadin for gluten-free food.