Introduction Goat milk and their dairy products are frequently adulterated with cow milk because of its smaller production in the world and its higher price compared to cow milk. However, the main benefit claimed about goat milk is that it is less allergenic than cow milk and is a suitable substitute, especially among children. Besides, cow milk proteins, even in low concentrations, are able to trigger allergic reactions.

Methods It was collected reliable samples of goat and cow milk. Afterwards, adulterations were performed adding different concentrations of cow milk (3%, 5%, 8%, 10%, 12%, 15% and 50%) in goat milk. Polyacrylamide gel electrophoresis (UREA-PAGE) and densitometry (ImageQuant TL) were used because this technique is simple and inexpensive to analyse proteins. Samples were applied in duplicate, obtaining two densitograms for each concentration. It was used bovine α_s1-casein to detect cow milk, because this protein fraction has a larger electrophoretic migration than caprine α_s1-casein.

Results Area peak of bovine α_s1-casein were directly proportional to the increase of concentration of cow milk and a linear regression was performed with the average of the duplicates: y=56.18x+1239. The linearity of the method could be observed because of high correlation (R²=0.9989).

Conclusion There is no official method to assure the absence of cow milk in goat milk and their dairy products in Brazilian legislation. Then this method can be easily introduced as a tool to detect this fraud, which may represent a dangerous for health population.