Detection of bovine milk in ovine yoghurt by electrophoresis of para-κ-casein

The possibility of detection and determination of bovine milk in adulterated yoghurt by cationic polyacrylamide gel electrophoresis (PAGE) of yoghurt caseins, treated with rennet, was examined. Yoghurts made from bovine and ovine milk and from known mixtures of the two were examined. The evaluation of bovine milk in yoghurt was based on the optical density of the bovine para-κ-casein band, which was distinctly separated and bore a linear relationship to the percentage of bovine milk in the mixtures. By using PAGE of bovine para-κ-casein, levels of bovine milk as low as 1% were easily detected in ovine yoghurt.