[Determination of wheat gliadins in food with ELISA]

Two Sandwich-ELISA methods suitable for quantitative determination of wheat alpha-gliadin and whole gliadin (i.g. alpha-, beta-, and gamma-gliadin) in unheated gluten-containing and gluten-free foods are described. An optimal method for extraction of gliadin from foods was developed. Foods are extracted with 70% ethanol except those containing cocoa, where 3 M-urea and 10% casein were added prior to extraction. Wheat flours are extracted at room temperature or at 40 degrees C, gluten-free foods at 40 degrees C. The recovery of added gliadin (0.1% wheat flour) is at least 80% in foods without cocoa, at least 70% in cocoa-containing foods (1% wheat flour added). Both methods are highly specific for wheat, cross-reactions e.g. with rye are insignificant. The sensitivity assay of the assay in buffer is 0.5 ng/ml alpha-gliadin an 10 ng/ml whole gliadin and it can be decreased by prolonged incubation with sample. The unspecific effect of food components is discussed; it can be eliminated to a large extent.