Functionality of β-Casein Peptides:  Importance of Amphipathicity for Emulsion-Stabilizing Properties

To investigate structure−function relationships with regard to emulsion-stabilizing properties, peptides from bovine β-casein (βCN), obtained by plasmin hydrolysis and fractionation of the hydrolysate, were isolated and identified on the basis of their masses determined by electrospray ionization mass spectrometry, the primary structure of the intact protein, and the known specificity of the enzyme. An amphipathic peptide fraction was fractionated further by ion-exchange chromatography and subsequent hydrophobic interaction chromatography resulting in the components βCN[f 1−105/107] and βCN[f 29−105/107]. The latter peptides had poor emulsion-stabilizing properties compared to the former ones, and the stability of an emulsion formed with βCN[f 29−105/107] was also more sensitive to hydrophobic impurities than that of an emulsion formed with βCN[f 1−105/107]. The highly charged N-terminal part appeared to be important for the emulsion-stabilizing properties of these peptides. A hypothesis for the structure−function relationship is given. Keywords: β-Casein peptides; plasmin; emulsion; mass spectrometry; structure−function relationship