Establishment of Goat Milk Forgery Detection Method Based on Casein Rapid Immunoassay

A competitive colloidal gold lateral flow strip was developed, evaluated, and used as a quick, sensitive, low-cost and convenient tool to identify the authenticity of goat milk on the market. By mixing cow milk with goat milk and testing, the detection range and sensitivity of the strip method were obtained. The effect of boiling and hydrolysis to strip were evaluated. The detection of α-casein and β-casein from cow and their hydrolysate by strip were also finished. Based on UPLC-Q-Exactive Orbitrap MS and the casein antibody affinity column, the purified peptides was identified by Peaks software. The identified peptides were artificially synthesized and tested by strips. The results showed that the limit of detection for qualitative judgment of goat milk adulteration was, by the naked eye, 1.2 mg/100 g and the cut-off value was 6 mg/100 g. The boiling and hydrolysis process had no effect to detection. At the same time, α-casein and β-casein could be detected, indicating this method could not distinguish and test the enzymatic hydrolysis α-casein and β-casein. Most of peptides obtained by multi-enzymes digestion could not bind to the casein antibody and the strip results indicating the casein antibody could not interact with artificially synthesized peptides too. In total, this strip could determine the intact structure of bovine casein in goat milk matrix, and could be used as an effective tool for authenticity identification.