| Abstract: | Triacylglycerol (TAG) molecular weight distribution and regioisomeric structure of selected molecular weight species in human milk and in 32 human milk substitutes was determined. Negative ion chemical ionization mass spectrometry was used to determine the molecular weight distribution and collisionally induced dissociation tandem mass spectrometry applied to identify the sn-2 and sn-1/3 positions of fatty acids in TAG. The main molecular weight species of human milk TAG in decreasing order of abundance were 52∶2, 52∶3, 52∶1, 54∶3, 50∶2, 50∶1, 54∶4, 48∶1, 54∶2, 48∶2, 46∶1, 52∶4, and 50∶3 (acyl carbon number/number of double bonds), constituting 83 mol% of total TAG molecular species. In human milk substitutes, the proportion of the corresponding molecular weight species varied from 33 to 87 mol%. The main TAG regioisomers within the molecular weight species 52∶2, 52∶3, and 50∶1 in human milk were 18∶1-16∶0-18∶1 (83 mol%), 18∶1-16∶0-18∶2 (83 mol%), and 18∶1-16∶0-16∶0 (80 mol%), respectively. In human milk substitutes, the corresponding proportions varied in a wide range of 0–82 mol%, 0–100 mol%, and 0–73 mol%, respectively. Although TAG structures in some human milk substitutes closely resembled those in human milk, the great variation among samples leads to the conclusion that it is still possible to improve the TAG composition in human milk substitutes by applying novel methods to synthesize structured TAG. |
