Detection and characterization of N-alkyl diethanolamines and N-2-alkoxyethyl diethanolamines in milk by electrospray ionization mass spectrometry

Milk is a highly nutritious food containing proteins, lipids, sugars, minerals, vitamins and other biologically active substances. The chemical composition of milk being studied by many research groups, however, there is a scope to explore with the emerging analytical techniques. As a part of application of shotgun metabolomics for studying milk metabolites, we have applied direct ESI-MS analysis of pasteurized milk and other raw milk samples (buffalo, cow, goat and human), after protein precipitation. Three series of ions that differ by 28 mass units were detected in the studied milk samples, and found that they have not been reported or characterized before. High resolution and tandem mass spectrometry experiments together with comparison of standard data or data interpretation were used to characterize the detected molecules. The detected molecules included N-alkyl diethanolamines, N-2-alkoxyethyl diethanolamines and N-alkyl ethanolamines (where the alkyl group is C-8-C-14), and these molecules were reported to show anti-bacterial and/or anti-microbial activity in the literature. The relative quantities of these molecules were measured using N-methyl diethanolamine as the internal standard and found that they were in the range of 2.3-27 ppm. The biochemical pathway of these molecules is yet to be established.