Development and Validation of a Lateral-flow Device for Detecting Total Milk Residues

Introduction: IgE-dependent and IgE-independent immuno-toxicities to cow’s milk constitute the most common causes of food “allergies,” affecting roughly 3% of the population. The most clinically significant allergens in milk are casein and beta-lactoglobulin (β-LG). Due to current food manufacturing practices, casein and β-LG can be present in food samples at very different levels, necessitating the use of dual casein and β-LG screening measures to correctly identify milk allergen contamination.

Purpose: To develop and validate a rapid detection kit that can specifically detect total milk residues from both swabs (at 0.01 µg/swab) and foods (0.1 ppm) in under 20 min.

Methods: Polyclonal antibodies (pAbs) against casein and β-LG were raised in goats and individually purified on affinity columns. The pAbs were then used to develop a lateral flow immunochromatographic assay configured in sandwich format. Sample extraction and running buffers were developed to enable rapid and highly sensitive operation of the lateral flow device (LFD). The ensuing Total Milk LFD kit was then validated.

Results: The Pi Bioscientific Total Milk LFD test method demonstrated a sensitivity of 0.01 µg/swab and 0.1 ppm milk protein for foods. The test was specific for bovine residues, and did not appreciably report caprine or ovine residues. Selectivity testing showed all spiked food matrices tested retarded LOD by 2-4 folds whereas real food testing showed highly detectable levels in all cow’s milk-based foods tested with the exception of goat or sheep’s milk-based foods. Specificity analysis revealed no cross-reactivity with common food commodities.

Significance: The development of a highly sensitive and rapid test method capable of detecting trace amounts of casein and/or β-LG in under 20 min should aid food manufacturers and regulatory entities in monitoring for milk allergens in environmental and food testing.