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The efficiency of reversed-phase HPLC, capillary electrophoresis (CE), PAGE and isoelectric focusing with immunoblotting in separating ovine caseins has been evaluated. The assessment was carried out by employing electrospray ionization–mass spectrometry (ESI–MS) and matrix-assisted laser desorption ionization–time of flight as reference tools for identifying protein components. Ovine casein was fractionated by HPLC into four major peaks. With ESI–MS, each peak contained components belonging to only one of the four casein families. On-line liquid chromatography–ESI–MS allowed us to determine each fraction's composition by detecting thirteen αs1-, eleven αs2-, seven β-, and three κ-casein (CN) components. The αs1-CN and αs2-CN consisted of eight and two protein chains respectively of lengths differing through the deletion of one or more peptide sequences; they were also discretely …