Current challenges in phospholipid analysis in bovine milk

Abstract

Phospholipids (PLs) are important components of milk fat globule membranes. They not only play the role of emulsifier ensuring the stability and homogeneity of the oil/water emulsion system of milk, but also have multiple beneficial functions vis-Ã -vis human health. PLs of milk are a complex family of polar lipids comprising several classes including PC, PE, SM, PS, PI, PA, PG and so on and each class contains a mixture of hundreds of molecular species differing in fatty acid (FA) composition and/or regio-position.Although PL quantification at the class level can be achieved by using NP-LC-ELSD and 31P-NMR, LC-MS (mainly HILIC-MS and RP-LC-MS) has become the prevalent analytical system for PL identification and quantification at the molecular species level. Unfortunately, combining LC separation with high-resolution MS detection is still insufficient to differentiate FA regio-isomers and double bond (DB) positional isomers, both being widely present in milk PLs. Additional techniques such as ozonolysis, UV-photodissociation and photochemical tagging in combination with LC-MS are needed for a complete structural characterization of PLs.Despite the recent progress, huge challenges remain to be overcome both in PL identification and quantification. This talk will discuss these in conjunction with the following aspects of bovine milk PLs. 1) pros and cons of different LC-MS methods in PL identification and quantification; 2) major PL class and species identified so far in bovine milk and 3) utility of Paterno-Buchi photochemical reaction in revealing regio-isomer and DB-positional isomers.