Milk Protein and Ingredient Analysis by Commercial Milk-specific LFD Kits

Introduction: Commercial lateral flow devices (LFDs) that target allergens are used by the food industry as a quick and rugged measure of equipment cleanliness or food product contamination. Milk LFDs that target total milk, casein or β-lactoglobulin are available, but little is known about their milk protein specificity and testing ability at high allergen levels which may produce false-negatives as a result of the hook effect.

Purpose: To determine the specificity of milk LFDs to milk proteins and milk-derived ingredients and to determine the overload level.

Methods: Casein (α-, β- and κ- casein) and whey proteins (α-lactalbumin and β-lactoglobulin) of milk were analyzed by eight milk (total milk, casein or BLG) LFDs.  Milk-derived ingredients (MDI)  (whey protein concentrate (WPC), sweet whey (SW), acid whey (AW), sodium caseinate (NaCas), non-fat dry milk (NFDM) and milk protein concentrate (MPC)) were analyzed with the eight milk LFDs and a total-protein kit. NFDM was tested with all of the kits to determine the overload level/hook effect.

Results: Some total milk LFDs only detected casein and not whey proteins. Similarly, some total milk kits did not detect MDIs containing only whey proteins (WPC, SW, AW). All LFD kits were able to detect NFDM. The LFDs became overloaded between 250 ppm -10,000 ppm NFDM protein; testing dilutions of a sample may be important to ensure it is within the dynamic range of the kit.  Variable intensities of LFD positive test lines were found throughout the allergen concentrations tested; LFDs are a qualitative test and corrective action should be taken whenever a positive result is obtained.

Significance: These results will help the food industry to effectively select a LFD for their purposes and interpret the test results.