Analysis of triacylglycerol regioisomers in plant oils using direct inlet negative ion chemical ionization tandem mass spectrometry

Triacylglycerols (TGs) are the primary lipids of plant oils and the positional distribution of fatty acids (FAs) is essential to physicochemical, functional, and nutritional qualities of oils. Most studies have reported TG species in plant oils. In some studies, FA combinations in each TG species have been reported still neglecting the regioisomer composition of TGs. In this study, a fast direct inlet negative ion chemical ionization tandem mass spectrometric (NICI-MS/MS) method and optimization algorithm were applied to study the regioisomerism of TGs in 18 different plant oils. According to FA composition results, oleic, FA 18:1(9); linoleic, FA 18:2(9,12); palmitic, FA 16:0 and stearic acid, FA 18:0 were the most abundant FAs, composing mainly TG species having acyl carbon numbers 50, 52 and 54 and 1-4 double bonds. Based on 35 detected TG species, oils were classified into five groups using clustering analysis. Each group had a different dominant TG species of which the most abundant were triunsaturated ones. In regioisomeric pairs or triplets, FA 16:0, FA 16:1(9), FA 18:0, and FA 18:2(9,12) were more commonly in the sn-1/3 position, while FA 18:1 slightly preferred sn-2. The most abundant TG regioisomers were: TG 16:0_18:1(sn-2)_18:1 (52:2, mainly 18:1 in sn-2) especially in avocado, macadamia nut, olive, and palm oils; TG 18:2_18:2(sn-2)_18:1 and TG 18:2_18:1(sn-2)_18:2 (TG 54:5, mainly 18:2 in sn-2) in corn, pumpkin seed, sesame, and sunflower oils. The use of high-throughput NICI-MS/MS method to study regioisomers in commercial plant oils contributes to further studies on profiling lipid structure and developing products with specific TG compositions to meet dietary needs. The regiospecific information of TGs in edible oils is crucial for understanding their health benefits and functional properties, which are in turn needed in selecting oils for various applications.