How to Manage a Positive Allergen Residue Result when Testing Your Food Product

Sample preparation can further contribute to analytical uncertainty, especially with certain types of particulates. For example, whole sesame seeds are difficult to break apart. If laboratories are using blenders to homogenize the sample before sub-sampling and extraction, they may find that the sesame seed remains intact. In that case, the sesame proteins will not be well distributed within the sample.

Every commercial ELISA kit has a stated dynamic range, such as 2.5 to 25 ppm in the earlier example. The kits should come supplied with a standard curve, and one of those standards should be the lowest concentration from the dynamic range—2.5 ppm in our example. In that situation, 2.5 ppm would be the lower limit of quantitation (LLOQ) of the ELISA method. But ELISAs also have lower limits of detection (LOD) that are below the LLOQ. The LOD is typically determined in a very passive matrix such as buffer. Some commercial laboratories will report positive results between the LOD and the LLOQ. This practice is questionable in our opinion because the matrix interference from the food being tested can generate weak low positive results between the LOD and LLOQ. Thus, it is important to find out the LLOQ of the ELISA method being used on your samples by the external laboratory and be mistrustful of any positive result reported below the LLOQ. These results could be false positives that will be very difficult to confirm.

Dr. Taylor is professor emerita of food science and technology and co-founder and co-director of the Food Allergy Research and Resource Program (FARRP) at the University of Nebraska-Lincoln. Reach him at [email protected]. Dr. Jayasena is a post-doctoral and senior researcher at FARRP. Niemann, Lambrecht and Kraft are lab managers at FARRP. Reach them at [email protected], [email protected], and [email protected]. Dr. Baumert is associate professor in the department of food science and technology at the University of Nebraska-Lincoln and co-director of FARRP. Reach him at [email protected].