Identification and quantification of native beta-casomorphins in Australian milk by LC-MS/MS and LC-HRMS

Beta-casomorphin 5 (BCM5) and beta-casomorphin 7 (BCM7) in 14 commercial pasteurised milks from around Australia were investigated using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and liquid chromatography-high resolution (Orbitrap) mass spectrometry (LC-HRMS). Collision induced dissociation HRMS was used to confirm the presence of BCM7 in milk extracts. The accurate mass-to-charge ratio (m/z) and relative abundance of BCM7 parent ion and fragments in milk extracts matched with those obtained from the analysis of a BCM7 standard solution. The deviation against the theoretical values of the measured m/z of BCM7 (parent ion and fragments) all gave results below 5 ppm (relative error). BCM5 was below limit of detection (LOD) for all milks, while BCM7 was between 0.13 and 2.38 ng/g in 10 milks and below LOD in the others. Pasteurised milks containing the highest and lowest BCM7 levels were produced in Western Australia.