Evaluation of indirect competitive and double antibody sandwich ELISA tests to determine -lactoglobulin and ovomucoid in model processed foods

Enzyme-linked immunosorbent assay (ELISA) kits (indirect competitive and sandwich formats) to determine either -lactoglobulin or ovomucoid were evaluated in model foods. A cut-off value was established for each kit to consider food samples as positive for milk or egg addition. Sausage and bread were positive at lower percentages of added milk using the sandwich format (0.005 and 0.05%) than the indirect competitive format (0.05 and 0.25%) and pate was positive at 0.25% milk addition for both formats. Sausage was positive at 0.005%, and bread at 0.05% added egg for indirect competitive and sandwich formats, whereas pate was positive at 0.25% egg only by the indirect competitive assay. The concentration of added milk and egg to give a positive result depends on heat treatment, being higher for pate (sterilised), followed by bread (baked) and sausage (pasteurised). The particularities of each format and the heat processing applied influenced the determination by ELISA of allergenic proteins in foods.