Chicken eggs are used extensively as an excellent source of dietary proteins. These proteins have many functional properties, making them valuable food ingredients. However, eggs are a frequent cause of food hypersensitivity, especially in children. Of major concern to food processors is the inadvertent cross-contact of food products with allergenic residues, which could result in potentially life-threatening reactions in those with a food allergy. Scientists, led by Doctors Hefle, Jeanniton and Taylor at the Department of Food Science and Technology, Nebraska, carried out a study to develop an enzyme-linked immunosorbent assay (ELISA) for the detection of undeclared egg residues in foods. Commercially purified ovalbumin (OVA) and dehydrated egg white solids were used as antigens to induce antibodies in rabbits and goats. Reference pasta standards and various food samples were extracted, then clarified by centrifugation. Goat anti-egg white antibodies were used as the capture reagent, non-specific sites were blocked with gelatine, then standard and sample extracts were added.
Rabbit anti-OVA antibodies were used as detector antibodies, followed by addition of commercial goat anti-rabbit IgG antibody labelled with alkaline phosphatase and subsequent substrate addition.
Twenty brands of egg-free pasta (two lots each) were analysed using the ELISA. Fourteen common pasta ingredients were also evaluated for cross-reactivity problems in the method.
The detection limit of the assay was 1 ppm spray-dried whole egg. Fifty-five per cent (22 samples) of the egg-free pasta samples tested positive for the presence of undeclared egg residues, with values ranging from 1 to more than 100,000 ppm. Minimal cross-reactivity was encountered in general, but portobello mushrooms and basil caused some minor matrix effects.
The scientists concluded that this sandwich-type ELISA method can be used to detect undeclared egg residues in processed foods and to evaluate industrial clean-up operations.
Full findings are published in the December issue of Journal of Food Protection: Vol. 64, No. 11, pp. 1812-1816