Abstract:
Abstract: Flaxseed Oil (FO) is one of the commonly-used edible vegetable oil in food production. But the complete lipid molecular composition and content are still unclear. This study aims to explore the true properties of the lipid composition in FO and discover the valuable lipid components. An ultra-high performance liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS) was used to characterize the lipid profile of FO. The results showed that there were the same lipid molecules in the three varieties of flaxseed (A, B, and C) oil. A total of 1 072 lipid molecules in 39 lipid molecule subclasses were identified in FO. In positive ion mode, a total of 668 lipid molecules in 15 lipid molecule subclasses were detected. In the negative ion mode, a total of 404 lipid molecules in 31 lipid molecules were detected. In both positive and negative ions mode, a total of 7 lipid molecules subclasses were detected. Among the 39 lipid molecule subclasses were detected under positive and negative ions, 30 lipid molecule subclasses are searchable in the LMSD database, while 9 lipid molecule subclasses are currently in the subclasses of the LMSD database could not be retrieved. Furthermore, 86 Diacylgycerol-N-trimethylhomoserine (DGTS) molecule species and 129 glyceroglycolipid molecule species glycosyldiacylglycerols (GlcADG), acylglycosyldiacylglycerols (AcylGlcADG), sulfoquinovosyldiacylglycerols (SQDG) and monogalactosyldiacylglycerols (MGDG), 151 ceramide lipid molecule species, 3 Gangliosides (GM3) molecule species and 3 Sphingomyelin (SM) molecule species, 32 FAHFA molecule species, 9 Fatty esters Acyl carnitine (ACar) molecule species and 1 Cholesterol molecule CE (18:2) were firstly found in FO. Among these subclass lipids, the triacylglycerols (TG) presented the largest number (471 molecule species) and the highest relative content (67.93%-68.91%), followed by diacylglycerols (DG), DGTS, and GlcADG. In addition, the content of 39 lipid molecule subclasses was compared in the three kinds of FO. It was found that there were significant differences between the GM3 and fatty acyl esters of hydroxy fatty acid (FAHFA) in the three kinds of FO (P<0.05), whereas, there was no significant difference among the other 37 lipids molecule subclasses (P>0.05). More importantly, a multivariate statistical model was also established to screen the different lipid molecules among different kinds of FO, in order to fully and accurately reflect the differences between the three kinds of FO. Specifically, the three varieties of FO were well distinguished in the unsupervised Principal Component Analysis (PCA). The difference among the three varieties of FO was greater than that within each group, which was explained by the supervised Orthogonal Partial Least Squares Discrimination Analysis (OPLS-DA). Furthermore, there were more than 200 lipid molecule species significantly different between the two varieties of flaxseed oil (P<0.05), where the marker lipid molecules of flaxseed A oil were further screened out as 6 PI molecules, 1 PC molecule,1 PE molecule, and 1 TG molecule. The marker lipid molecules of flaxseed B oil were 6 TG molecules and 1 HBMP molecule. The marker lipid molecules of flaxseed C oil were 1 GM3 molecule and 1 SQDG molecule. Correspondingly, these lipid molecules were used as the markers of the three types of FO, suitable for the quality and authenticity identification, as well as the nutritional and safety evaluation of vegetable oil. In summary, 39 subclasses totaling 1 072 lipid molecule species were identified in FO. There were also significant differences in the lipid molecular level of different FOs. A total of 415 lipid molecule species in the 22 subclasses were found, which has not been reported yet in FO. This discovery can make a sound theoretical foundation to develop the nutritional value of FO, particularly for the comprehensive and systematic investigation of the lipid profile in other lipid foods.