Mass spectrometric analysis of phosphatidylcholine regioisomers in human milk and infant formulas

Human milk is widely recognized as the optimal source of infant nutrition. The development of infant formulas resembling human milk has been an ongoing challenge over the past decades. Phospholipids (PLs), key structural components of the milk fat globule membrane (MFGM), have a multitude of nutritional implications. Although the general composition of MFGM in human milk is well-established, a more detailed structural analysis of its components is important for advancing infant formula development and enhancing their nutritional value. One understudied aspect is the positional distribution of fatty acids (FAs) in individual PL compounds (regioisomers) in human milk.

This study investigated the regioisomeric composition of phosphatidylcholines (PCs) in human milk and various commercial infant formulas, employing a novel tandem mass spectrometric (MS/MS) methodology coupled with a computational algorithm. We used the relative abundances of the structurally informative FA fragments to quantify the ratios of regioisomers. A total of 62 different PC regioisomers were detected in the human milk and infant formula samples. Our findings reveal differences between human milk and infant formulas in some PC regioisomer pairs, most notably those containing FA 18:1. For instance, in human milk the ratios of a major PC regioisomer pair PC 16:0/18:1 and PC 18:1/16:0 were 18 % and 82 %, respectively, whereas these ratios were almost reversed in infant formulas.

It has been generally believed that in natural PLs unsaturated FAs are predominantly esterified to the sn-2 position when paired with saturated FAs, but these results show that this is not always the case, highlighting the need for further investigation on the biochemical and nutritional implications of the unique regioisomer profile in human milk. This study contributes to the ongoing efforts to develop infant formulas that more closely resemble the nutritional profile of human milk.