Quantitative determination of bovine κ-casein macropeptide in dairy products by Liquid chromatography/Electrospray coupled to mass spectrometry (LC-ESI/MS) and Liquid chromatography/Electrospray coupled to tamdem mass spectrometry (LC-ESI/MS/MS)

κ-Casein macropeptide (CMP) is a polypeptide of 64 amino acid residues, derived from the C-terminal part of bovine κ-casein. It is a complex mixture of non-glycosylated and variously glycosylated forms. Using reversed phase-high pressure liquid chromatography (RP-HPLC) coupled to a mass spectrometer fitted with a electrospray ionisation source (ESI-MS) sensitive, reliable and specific methods were developed to enable unequivocal determination of aglyco-CMPA, aglyco-CMPB and total CMPAB. Several selective detection methods were proposed for their quantification. Aglyco-CMPA and aglyco-CMPB were quantified, respectively, from 13595+, 16984+, 22643+ and 13525+, 16904+, 22533+m/z specific ions from multiple ion monitoring (MIM) mode. Within-day repeatability and between-day repeatability were 1% and 5%, respectively, with a standard deviation lower than 1%. Total CMPAB was quantified from peptide κ-CN (162-169) released from pepsin hydrolysis using UV, single ion monitoring (SIM) and multiple reaction monitoring (MRM) detection. A high degree of selectivity was obtained using MRM detection; the limit of quantification was 10 pmol within the standard curve range of 10-1000 pmol. Several commercial products were analysed and data obtained were in agreement with those indicated in the literature.