Driven by the urgent market demand for milk traceability technologies, a microdroplet digital polymerase chain reaction (PCR) assay was developed to accurately identify the milk source in goat milk powder. This method overcame the shortcomings of complex ingredients and long time required for identifying the source of milk, and could detect it more accurately and reduce the possibility of misjudgment. In this study, a model equation for describing the relationship between the number of DNA copies per μL from goat milk powder (C) and its mass (M, mg) was proposed as follows: M = (C−4.75)/3.56.

This study established a fluorescence-based quantitative real-time polymerase chain reaction method for the detection of caprine-derived ingredients in milk powder. The specificity, sensitivity, and stability of the caprine-specific primers were evaluated. By linear fitting of the difference in cycle threshold (ΔCt) as a function of the mixing proportion between goat and horse milk powder, a calibration curve for the relative quantitation of caprine-derived ingredients in milk powder was established as follows: y = 0.7209x + 5.6519 (R² = 0.9875), and the minimum detection limit of this method was 0.0001 ng/μL. The recoveries of the proposed method were 96.22%-112.00%, and the inter- and intra-group coefficient of variation was ≤ 0.79% and ≤ 1.77%, respectively.