Abstract
Regioisomers (or positional isomers) of triacylglycerols (TAGs) of milk are known to show differential outcome in relation to human absorption. Quantitation of TAG regioisomers remains a big challenge due to the lack of facile chromatographic separation technique. The feasibility of using fragment ion intensity ratio to determine the ratio of co-eluting AAB/ABA-type regioisomer pairs was confirmed in this study. The ability of C30 stationary phase in resolving interfering TAG isomers was demonstrated for the first time. This allowed us to reveal the complexity of using fragment ion intensity to quantify 1,2-olein-3-palmitin (OOP), 1,3-olein-2-palmitin (OPO), 1,2-olein-3-stearin (OOS), and 1,3-olein-2-stearin (OSO) regioisomers in milk samples. A novel algorithm was proposed to consider the contribution of OPO/OOP and OSO/OOS double bond (DB)-isomers and to eliminate the interference of isobaric ions from other isomers, an aspect overlooked in previous studies. This liquid chromatography-mass spectrometry method that requires no pre-fractioning and a moderate chromatographic separation time of 36 min is simple and, thus, suitable for screening a large number of samples for genetic analysis of this trait. Preliminary results using a small cohort of animals showed that OPO/OOP ratio differs significantly between Jersey and Holstein cows, and a large variation was also observed across individual Holstein cows.
Highlights
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Chromatographic separation of OPO/OOP and OSO/OOS pairs was not achieved with the C30 column (Figure 1A); increasing the gradient elution to 50 min did not make noticeable improvement on the separation
Among all the reversed-phase columns used in lipidomic analysis, only a non-endcapped polymeric ODS
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Lipids are one of the major nutritive components of human and bovine milk alongside lactose and proteins, whereas triacylglycerols (TAGs) are the dominant fraction (>95%). Of milk lipids [1]. TAGs are small molecules (MW < 1200 Da) containing three fatty acids (FAs) esterified to the three positions (named sn-1, sn-2 and sn-3) of glycerol backbone
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