Detection of milk-derived peptides in human blood post-digestion, using LC-MS/MS

Milk-derived whey protein isolate (WPI) and glycomacropeptide (GMP) have an array of bioactivities such as antibacterial and immunomodulation. However, it is unclear whether they exert their bioactive functions beyond the gastrointestinal tract. Therefore, this study aimed to detect GMP-derived fragments in blood post-in vitro digestion and spiking and determine the presence of WPI- or GMP-derived peptides in vivo from the blood of three young adults and 15 elderly adults post-ingestion of a WPI shake. Milk-derived peptides were extracted from all plasma samples using size exclusion chromatography and solid phase extraction and analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Forty-three peptides were detected in the digested GMP-spiked plasma samples. Seventy-five milk-derived peptides were discovered in the plasma of one WPI-fed subject, many of which were homologous to bioactive sequences. No milk peptides were identified in other subjects’ plasma samples. This work provides evidence for inter-individual variation in milk-derived peptide absorption.