EN
A method is described for the determination of bovine milk in cheeses by polyacrylamide gel isoelectric focusing according to EC reference method on ready-to-use gel plates. The advantages of this method are easy to use handling and good reproducibility by application of ampholytes with high concentration of urea. The method includes (i) recovery of cheese proteins fat and salt free; (ii) hydrolysis of cheese proteins with plasmin; (iii) separation by isoelectric focusing at pH 3–10 of bovine, ovine, caprine and buffalo γ-caseins according to their different isoelectric points and the densitometric evaluation of the electrophoretic bands. With the modification of the reference method the addition of cow milk to samples of goat and goat/ewe milk cheeses was proven.