Utilizing linkage-specific ethyl-esterification approach to perform in-depth analysis of sialylated N-glycans present on milk whey glycoproteins

Glycosylation of milk whey proteins, specifically the presence of sialic acid-containing glycan residues, causes functional changes in these proteins. This study aimed to analyze the N-glycome of milk whey glycoproteins from various milk sources using a linkage-specific ethyl esterification approach with MALDI-MS (matrix-assisted laser desorption/ionization-mass spectrometry). The results showed that the N-glycan profiles of bovine and buffalo whey mostly overlapped. Acetylated N-glycans were only detected in donkey milk whey at a rate of 16.06%. a2,6-linked N-Acetylneuraminic acid (a2,6-linked NeuAc, E) was found to be the predominant sialylation type in human milk whey (65.16%). The amount of a2,6-linked NeuAc in bovine, buffalo, goat, and donkey whey glycoproteomes was 42.33%, 44.16%, 39.00%, and 34.86%, respectively. The relative abundances of a2,6-linked N-Glycolylneuraminic acid (a2,6-linked NeuGc, Ge) in bovine, buffalo, goat, and donkey whey were 7.52%, 5.41%, 28.24%, and 17.31%, respectively. Goat whey exhibited the highest amount of a2,3-linked N-Glycolylneuraminic acid (a2,3-linked NeuGc, Gl, 8.62%), while bovine and donkey whey contained only 2.14% and 1.11%, respectively.