Characterization of Silter Cheeses Produced in Valley and Alpine Pastures by a Proteomic Approach

Silter is an Italian hard cheese manufactured with milk produced by cows fed at different altitude, valley or alpine pasture. The chemical, rheological and sensory properties of cheeses can be affected by the modification in milk composition due to the breed which at different altitude causes the modification of protein content, ?-CN glycosylation, plasmin activity, and coagulation properties. The influence of milk plasmin activity on dairy production was investigated in seven Silter cheeses, four produced in the valley and three from alpine mountain, through alkaline urea-polyacrylamide gel electrophoresis; two-dimensional gel electrophoresis coupled to mass spectrometry and image analysis. Results demonstrated that Silter cheese obtained from cows reared in alpine pasture is characterized by a more evident proteolysis, determining high levels of ?-CN and ?s1-CN fragments. Therefore, the most relevant fragmentation was attributed to a more intense activity of plasmin and to a different dosage of rennet to make up for the reduced coagulation properties of alpine milk.