Gluten fragment detection with a competitive ELISA.

The second generation of a competitive ELISA for prolamin quantification based on the R5 antibody was studied for method performance and suitability to detect partially hydrolyzed prolamins in food. To be able to convert signal intensities to gluten concentrations, as required by the Codex Alimentarius Standard, a new calibrator consisting of a peptic-tryptic digest of wheat, rye, and barley prolamins was used for the first time. LOD and LOQ of the assay were 1.36 and 5.0 mg prolamin/kg food, respectively. Analysis of beer samples and a hydrolyzed wheat product showed that the assay provided significantly higher prolamin concentrations, compared to the sandwich ELISA based on the same antibody, which is only suitable for the detection of intact prolamins. Spiking experiments with defined concentrations of partially hydrolyzed prolamins gave recoveries ranging from 92 to 136%.