Assessment of the gluten content in gluten-free labeled foods: comparison of two gluten detection methods

Abstract

This study was designed to compare the effectiveness of the R5-ELISA and immunochromatographic assays in detecting gluten in foods labeled gluten-free and to determine if the immunochromatographic method is a sensitive and reliable method for detecting gluten at safe levels for celiac patients. We analyzed seventy different commercially foods available in Brazil, labeled “gluten-free”. Gluten was extracted by ethanol precipitation and, subsequently, analyzed using a commercial immunochromatographic test and ELISA kit, both based in a monoclonal antibody. The analysis of sensitivity and specificity was made using the kappa coefficient. More than a quarter of the samples (28.6%) analyzed by ELISA contained levels of gluten greater than 5 mg/kg. Almost half of these (12.9%) exhibited levels that exceeded 20 mg/kg, the maximum gluten level recommended by the Codex Alimentarius for a naturally gluten-free product. We found 27.1% of the samples tested positive in the immunochromatographic test. There was no statistically significant difference between the results of the ELISA (detection value ≥ 5 mg/kg) and the immunochromatographic test. Comparing the ELISA (≥ 5 mg/kg) and immunochromatographic test, we obtained 90% sensitivity and 98% specificity (Kappa of 0.89). We found gluten in a high proportion of the samples tested using both methods. In this study we also demonstrate that the immunochromatographic method is nearly as sensitive as the ELISA in detecting gluten levels and thus may serve as an inexpensive and rapid alternative to the R5-ELISA screening test.