Conversion of DNA Copy Number Ratios to Mass Fractions for Quantifying Chicken Adulteration in Duck Meat by Digital...

Meat adulteration, particularly the substitution of duck with chicken, threatens food authenticity, consumer trust, and regulatory compliance. However, converting DNA copy number measurements into meat mass fractions remains challenging. This study developed a digital PCR (dPCR)-based quantitative for determining chicken in duck. Singleplex and duplex dPCR assays targeting single-copy nuclear genes specific to chicken, duck and the conserved myostatin gene were developed and optimized. Five sets of binary chicken-in-duck mixtures were prepared and analyzed across 0-100% (w/w) to account for biological variability among meat sources. Five conversion approaches were evaluated: two conversion factor approaches based on the chicken-to-duck (k_cd) and chicken-to-myo (k_myo) copy number ratios, two corresponding approaches without conversion factors (No_kcd and Myo), and a linear regression model (Std). Quantitative performance of all five conversion approaches was concentration-dependent, and no single approach was optimal across the entire range. Conversion factor approaches generally improved agreement with gravimetrically assigned values at low to intermediate levels but overestimated higher chicken fractions. The Std approach performed well at ≥5% (w/w) but was less reliable at lower levels. Approaches selected based on their quantitative performance were further evaluated across different sample compositions and processing conditions and applied to commercial duck products. Overall, dPCR combined with an appropriate conversion approach may support quantitative determination of chicken in duck meat for food authenticity testing.