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.

In order to improve the detection efficiency of molds and yeasts in low-temperature yogurt, primers and probes were designed according to the sequences of the conserved gene elongation factor-1α (EF-1α) for molds and yeasts, respectively. A real-time fluorescence quantitative polymerase chain reaction (real-time PCR) method with TaqMan probe was established for the detection of molds and yeasts, respectively. The genomic DNA of fungi and lactic acid bacteria commonly found in low-temperature yogurt, were used as amplification templates for specificity testing. The sensitivity and repeatability were also tested, and the standard curves were constructed. The results showed that the designed primers and probes had good specificity; the sensitivity of the method was 10¹ and 10² CFU/mL for yeasts and molds, respectively; the coefficients of variation within and between groups in the repeatability test were less than 2%, indicating good reliability and stability; the correlation coefficients of the standard curves were higher than 0.99. Therefore, the real-time PCR method enables the rapid detection of molds and yeasts in low-temperature yogurt.

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.