Gluten Analysis of Wheat Starches with Seven Commercial ELISA Test Kits-Up to Six Different Values

The use of purified wheat starch (WSt) as part of the gluten-free diet for celiac disease (CD) patients is considered safe in many countries, but uncertainties about residual gluten amounts remain. Enzyme-linked immunosorbent assays (ELISAs) are most commonly used to monitor compliance to the Codex threshold of 20 mg gluten/kg of the product, but the analytical results for one sample may differ depending on the characteristics of the test kit. This study aimed to compare a representative collection of ELISAs regarding their ability to quantitate gluten contents of WSt. The gluten contents of 30 WSt (14 declared as gluten-free) and one defined assay control were analyzed with seven commercial ELISA test kits using the respective recommended extraction protocol for WSt samples. The comparative analysis of gluten yielded up to six significantly different results per WSt. In 13 samples, at least one kit found gluten contents below 20 mg/kg and at least two kits found gluten contents above 20 mg/kg, which would affect accurate labeling of the WSt depending on the kit used. The results of different kits were only partly correlated to one another. The different specificities and sensitivities of the various test systems were most apparent at levels between the regulatory threshold of 20 mg gluten/kg and the respective limits of quantitation. To ensure the safety of gluten-free products for CD patients, it is important to know which test kit is best suited to reliably detect gluten traces in a variety of food matrices.