Triacylglycerols (TAGs) are the most abundant components in edible plant oils, dominating over 95% of total lipids. Fatty acids (FAs) are composition units of TAGs, which provide distinctive properties of fat and oils. TAGs with the same numbers of acyl carbons (ACN) and double bonds (DB) may have different fatty acids, and even TAGs containing the same FAs may have different molecular structures i.e. regio- and stereoisomers depending their positions in the molecules. TAG regio-isomers differ in physicochemical properties and metabolic characteristics.
In this study, TAG regioisomers were analyzed of 18 plant oils bought from Finnish market, using direct inlet negative ion chemical ionization tandem mass spectrometry (NICI-MS/MS). Totally 33 ACN:DB species of TAGs were detected, and the regioisomers were identified and quantified for the dominating TAG species. Oleic acid (18:1n-9, O), linoleic acid (18:2n-6, L), and palmitic acid (16:0, P) were the three most abundant FAs resulting in TAGs of ACN 50, 52, and 54 as the most abundant TAGs in these oils. The dominant regioisomer pairs of these major TAG species of were LLL (54:6), LLO/LOL (54:5, mainly L in sn-2), LOO/OLO (54:4, mainly O in sn-2), OOO (54:3); PLL/LPL (52:4), POL/PLO/LPO (52:3, mainly O and L in sn-2), POO/OPO (52:2, mainly O in sn-2); PLP/PPL (50:2, mainly L in sn-2), POP/PPO (50:1, mainly O in sn-2), where the sn-2 FAs are listed in the middle positions. Unsaturated FAs more commonly distributed in sn-2 position compared with saturated FAs. Additionally, palm, avocado, and oat oils, where TAG of ACN:DB 50:1 represented 22.0, 5.7, and 5.2 mol%, sequentially of the total TAGs, contained considerable amounts of PPO with palmitic acid in the sn-2 position (23.5, 33.9, and 25.1 mol%, sequentially), indicating potential of these oils as ingredients of human milk fat substitutes for infant formulas.
This is the first study comprehensively analyzed the regioisomeric composition of TAGs with rapid NICI-MS/MS method. This high-throughput NICI-MS/MS method without need of chromatographic separation is suitable for determining regioisomers in massive TAG pools. The information of TAG regioisomers in this study provides valuable reference for further studies on fat- or oil-based products, such as infant formulas, dairy alternatives, and food supplements.