Screening of Melamine in Milk and Milk-based Products Using Enzyme-linked Immunosorbent Assay

Background and Objectives: Melamine is an organic nitrogen used as an adulterant to increase nitrogen and protein contents in milks. Enzyme-linked immunosorbent assay has verified as a good alternative for rapid screening of melamine and other food additives instead of the laborious chromatography techniques. Materials and Methods: In the present study, MaxSignal enzyme-linked immunosorbent assay kit was used to screen melamine in 30 samples, including milks, infant formulas, chocolates, tea whiteners and pet foods. The kit was based on a competitive colorimetric enzyme-linked immunosorbent assay. Results: Melamine was detected in the range of 0.05–0.69 ppm in infant formula/milk powder samples and 0.001–0.042 ppm in liquid milk samples, which were under the set limits of Codex Alimentarius, 2012. Codex Alimentarius Commission adopted a maximum melamine level of 1 ppm for powdered infant formulas and of 2.5 ppm for other foods and animal foods. The commission has now set a maximum limit of 0.15 ppm for melamine in liquid milks. Further protein analyses of milk and infant formula samples were also carried out to verify the presence of melamine. Conclusions: It has been seen that enzyme-linked immunosorbent assay could effectively be used as a screening tool for detecting melamine in a wide range of food samples. Whereas, complementary techniques such as high-performance liquid chromatography, gas chromatography/mass spectrometry can be adopted as verification methods for regulatory compliance.