Choose the right swab. Swabs must remove protein residues that may adhere to equipment surfaces, but must also be adsorbent. Swabs must also release the proteins back into an extraction solution. The swabs provided with commercial kits, such as the environmental swabs from Neogen, outperform regular cotton swabs.
Sponges should be avoided for allergen testing, as they tend to hold on to proteins, failing to release them into extraction solutions. Furthermore, some sponges may contain microbial growth media made from allergenic foods such as milk and soy.
Choose the most appropriate test method. The choice of an LFD that fits your purpose is relatively straightforward: It must be able to detect the allergen residues in the product matrix of concern. Essentially, will the LFD detect residues on the equipment surface before cleaning?
Different commercial LFDs targeted at residues of the same allergenic food are not created equal. LFDs contain antibodies raised against the allergenic food or specific proteins from the allergenic food. Each commercial LFD kit has its own proprietary antibody/ies that may respond differently to the residues left on equipment surfaces. Food companies use a variety of ingredients derived from a particular allergenic food (e.g., milk-derived ingredients can include non-fat dry milk, caseinates, or whey derivatives). Don’t assume that a given LFD will detect all forms of milk equally well—some commercial milk LFDs do not detect whey or whey-based ingredients, for instance. The sensitivity levels of different commercial kits for the same analyte will also vary and be dependent on the nature of the ingredient derived from the allergenic source.
Processing conditions also affect a system’s ability to detect allergen residues on equipment surfaces. Heat processing causes protein aggregation, resulting in difficulty with removal of residues from the surface and challenges with solubilization. Fermentation can alter proteins through proteolysis, again affecting antibody recognition on the LFD.
False negative results due to overloading LFDs is a particularly important concern. Due to the “hook effect,” high levels of allergen residues can cause false negatives. The hook effect occurs when high levels of the allergen residue are present, which overwhelms the detector antibodies in the strip causing most (perhaps all) of the allergen-antibody complexes to miss binding to the allergen-specific antibodies bound at the test line in the strip—resulting in a false negative response. Some commercial LFDs have overload lines while others do not, and the level of allergen needed to generate a false negative due to overloading will be different for each commercial kit. With milk, overloading occurs at concentrations from 100 ppm up to >10,000 ppm (expressed as ppm NFDM), depending upon the type of commercial kit. Serial dilutions of the swab or CIP rinse water extraction solution can be used to avoid overloading.
Set an achievable cleaning goal. LFD swabs are used to validate the effectiveness of SSOPs for removal of detectable allergen residues from shared equipment surfaces (or CIP final rinse water). Each product and processing line should be evaluated separately. If formulations have similar physical attributes (e.g., dry powders), similar cleaning approaches can be used on multiple formulations. When formulations contain multiple allergens, the assessment can sometimes be limited to the allergen that is present in the highest allergen load.
A corporate target level for effective allergen cleaning should be set, such as no detection of allergen residues on swabs using a specific LFD with a particular sensitivity level (e.g., no detection of milk protein residues with an LFD having a detection limit of 5 ppm). The LFD sensitivity level will vary to some degree with the nature of the food matrix, but a general statement such as “no detection by swab with LFD” is usually sufficient.