Identification of bioactive peptides and quantification of β-casomorphin-7 from bovine β-casein A1, A2 and I after ex vivo gastrointestinal digestion

This study investigated whether different genetic variants of β-casein (β-CN) give rise to different bioactive peptides during digestion. β-CN was purified from bovine milk of genetic variants A1, A2 and I, and digested with human gastrointestinal juices in a static ex vivo model. Mass spectrometry analyses revealed that the peptide 60YPFPGPIPN68 was exclusively identified from variants containing proline at position 67. Most strikingly, the opioid peptide β-casomorphin-7, 60YPFPGPI66, was identified from both variants A1 and A2 after simulated digestion, though with concentration being somewhat higher after digestion of the variant A1, compared with variants A2 and I. The peptides 134HLPLP138 and 133LHLPLP138 were both identified after initial 5 min of duodenal digestion. In conclusion, genetic variation of β-CN may affect proteolysis during digestion; however, the release of β-casomorphin-7 (BCM7) does not seem to be linked solely to variant A1, as earlier suggested by relevant published literature on in vitro digestion.