Peptidomic approach based on combined capillary isoelectric focusing and mass spectrometry for the characterization of the plasmin primary products from bovine and water buffalo β-casein

The main peptides produced by hydrolysis of water buffalo β-casein with plasmin were characterized by capillary electrophoresis and mass spectrometry and compared with their bovine homologous. A novel breakdown product arising from the hydrolysis of water buffalo β-casein, originated by the presence of a plasmin-sensitive Lys bond at position 68 was identified, which was not present in bovine β-casein. On the basis of this evidence, an improved procedure for the detection and the differentiation of the products of plasmin hydrolysis of bovine and water buffalo β-casein by capillary isoelectric focusing was set-up. In the experimental conditions, the γ-casein from the two species was efficiently separated. Comparison of the capillary electropherograms with those obtained by ultra-thin-layer isoelectric focusing, the reference method for routine analysis of plasmin digests of casein, suggests that capillary electrophoresis isoelectric focusing may constitute a successful alternative to the traditional slab gel electrophoresis analysis of plasmin digests of casein either for basic structural studies or for applications in the quality assessment of dairy products.