DNA-based detection of milk adulteration in dairy products from the Greek market

Milk adulteration, particularly the undeclared addition of cow's milk to higher-value sheep and goat dairy products, poses significant health, economic, and regulatory challenges. Given the central role of small-ruminant dairy production in Greece—one of Europe's largest producers of sheep and goat milk—monitoring authenticity is critical for protecting both consumers and the national agri-food economy. In response to growing global demand and increasing incidents of fraud, this study conducted the first comprehensive survey of milk authenticity in the Greek market using an optimized and validated TD-PCR protocol. Three DNA extraction kits were evaluated using spiked cheese and yogurt samples, with the automated Maxwell RSC system (Promega) showing the highest recovery efficiency and minimal contamination risk. The TD-PCR method achieved high sensitivity, with a limit of detection as low as 1 % cow DNA in yogurt and up to 5 % in cheese matrices. Analysis of 74 commercial dairy products revealed widespread adulteration, particularly in goat yogurts (40 %) and cheeses (40 %), as well as in three kefirs and several mixed and whey-based cheeses. Notably, only 7 out of 17 feta samples contained detectable goat DNA, suggesting possible mislabeling. Overall, the developed approach provides a robust and scalable molecular tool for routine authenticity testing, supporting regulatory enforcement, fair trade, and consumer confidence in Greek dairy products.