Comprehensive Characterization of Bovine Milk Lipids: Triglycerides

A comprehensive
survey on triglycerides (TAGs) of bovine milk was
conducted by a combination of exhaustive liquid chromatography (LC)
separation, high-resolution mass spectrometry (MS) detection, and
automated lipid molecular feature extraction. A total of 220 groups
(a series of species having the same chemical formula and mass) and
3454 molecular species of TAGs were identified based on the accurate
mass of the parent ion as well as MS2 information. Sixty-five different
fatty acids (FAs) were found across these TAG species; C4:0, C6:0,
C8:0, C10:0, C12:0, C14:0, C16:0, C18:0, and C18:1 were the most frequent
FAs, whereas C11:3, C11:4, C27:0, C27:1, C28:0, and C28:1 were rare
FAs in TAG molecules. The number of species identified represents
only a small portion of total TAG molecules that can be theoretically
synthesized from 65 FAs. Each TAG group contains on average 15–16
isomeric species (species with different FA composition), but positional
isomers do not seem to be widespread. As the isomeric species cannot
be completely resolved chromatographically, quantification of TAG
was conducted at the group level. The most abundant TAG groups in
bovine milk include TAG 34:0, TAG 36:0, TAG 38:1, TAG 38:0, and TAG
40:1. This study provides the most comprehensive milk TAG inventory
so far that can be used as a reference for studying milk lipids.