Development of a sandwich enzyme-linked immunosorbent assay for the detection of egg residues in processed foods

Chicken eggs are used extensively as an excellent source of dietary protein s. These proteins have many functional properties, making them valuable foo d ingredients. However, eggs are a frequent cause of food hypersensitivity, especially in children. Of major concern to food processors is the inadver tent cross-contact of food products with allergenic residues, which could r esult in potentially life-threatening reactions in those with a food allerg y. The aim of the present study was to develop an enzyme-linked immunosorbe nt assay (ELISA) for the detection of undeclared egg residues in foods. Com mercially purified ovalbumin (OVA) and dehydrated egg white solids were use d as antigens to induce antibodies in rabbits and goats. Reference pasta st andards and various food samples were extracted, then clarified by centrifu gation. Goat anti-egg white antibodies were used as the capture reagent, no nspecific sites were blocked with gelatin, then standard and sample extract s were added. Rabbit anti-OVA antibodies were used as detector antibodies, followed by addition of commercial goat anti-rabbit IgG antibody labeled wi th alkaline phosphatase and subsequent substrate addition. Twenty brands of egg-free pasta (two lots each) were analyzed using the ELISA. Fourteen com mon pasta ingredients were also evaluated for cross-reactivity problems in the method. The detection limit of the assay was I ppm spray-dried whole eg g. Fifty-five percent (22 samples) of the egg-free pasta samples tested pos itive for the presence of undeclared egg residues, with values ranging from 1 to > 100,000 ppm. Minimal crossreactivity was encountered in general, bu t portobello mushrooms and basil caused some minor matrix effects. This san dwich-type ELISA method can be used to detect undeclared egg residues in pr ocessed foods and to evaluate industrial clean-up operations.