Regio-distribution and double bond locations of unsaturated fatty acids in phospholipids of bovine milk.

ABSTRACT

Hundreds of phospholipid (PL) species with defined fatty acid (FA) composition have been identified previously in bovine milk using liquid chromatography tandem mass spectrometry (LC-MS/MS). Paterno-Buchi photochemical reaction coupled with LC-MS/MS was applied in this study to further unravel the regio-distribution and double bond (DB) locations of FAs. Using SPE-purified PLs and 2-acetylpyridine as the photochemical derivatization reagent, we were able to reveal the non-specific regio-distribution of unsaturated FAs and the widespread occurrence of regioisomers in milk PLs. Although Δ9 and Δ9,12 were found to be the predominant DB location(s) for C181 and C182 respectively, other DB positional isomers such as C181Δ11, C181Δ12 and C181Δ13 and C182Δ9,11 were widely detected in PL structures, implying that the minor isomers of C181 and C182 equally participate in the synthesis of PLs. Our study provides novel information on the fine structure of milk PLs and further underlines the complexity of milk lipid composition.