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.