Quantification of cow milk in adulterated goat milk by HPLC-MS/MS using N-acetylglucosamine as a reliable biomarker of cow milk

This study aimed to develop a non-protein-based method for quantify cow milk in adulterated goat milk. The raw cow milk and raw goat milk samples were mixed separately with the same volume of cold acetone and centrifuged to remove their proteins. The supernatants were evaporated, and the residues were derivatized by silylation followed by GC-MS analysis. N-acetylglucosamine was identified as a thermostable non-protein biomarker of cow milk. Its concentration in the raw cow milk (146.7 mg/L) was 32 times higher than that in the raw goat milk. On this basis, a HPLC-MS/MS method using positive-ion electrospray ionization in parallel reaction monitoring mode was developed for quantifying cow milk in adulterated goat milk by determining peak area of the biomarker. The method showed good linearity over cow milk concentrations of 1-100% and could detect as low as 0.3% cow milk in adulterated goat milk. Besides, the method was characterized by a simple sample pretreatment process, rapid detection, high accuracy, and high precision. With this method, a sample could be analyzed in 10 min. The present study demonstrated the feasibility of quantifying cow milk in adulterated goat milk using N-acetylglucosamine as a biomarker of cow milk.