ELISA Test May Miss Milk-Protein Residues

SAN DIEGOThe standard test used to detect milk-protein residues in processed foods may not work as well as previously believed in all applications, sometimes missing ingredients that can cause milk allergy, according to new research presented at the 243rd National Meeting & Exposition of the American Chemical Society (ACS).

Food processors use the enzyme-linked immunosorbent assay (ELISA) standard test to assure that processed foods that do not contain milk and processing equipment in facilities that process milk products are free of milk allergens, the substances that can trigger milk allergy. An ELISA kit for milk proteins contains antibodies that bind to milk proteins that may be in a finished food product or on the surface of shared manufacturing equipment. If a sample taken from a finished product or from the surface of food-processing equipment contains milk residue, a color change will occur in the test, indicating a positive result for contamination with milk proteins.

The researchers studied and documented how ELISAs perform on several measures of accuracy when milk proteins undergo changes in foods that are boiled, baked, fried or heated in other ways. They found thermal and non-thermal processing of foods can make milk proteins aggregate together so it is difficult to get the milk proteins into solution, which enables them to be detected by the antibodies in ELISAs. The clumping, however, does not necessarily destroy the proteins ability to trigger an allergic reaction in sensitive people. Clumped-together proteins also would be likely to maintain their potency once they reached the human body, he added. Heating and other processing also can alter the structure of the protein, which can affect the ability of the antibody to bind to the milk proteins. Alteration in the protein structure does not necessarily mean that the milk proteins become non-allergenic for the majority of milk-allergic individuals.

The results of these studies could be utilized by commercial ELISA kit manufacturers to aid in improving ELISAs for detection of milk residue in processed food products. These improved tests can be adopted by the food industry, if necessary, to allow for reliable detection of milk residue regardless of the type of processing that is used," the researchers said. These improvements should not result in commercial tests that are more expensive or difficult for food processors to use."