Abstract: An ultra-high performance liquid chromatography coupled to orbitrap high resolution mass spectrometry (UPLC-Orbitrap HRMS) method was developed to characterize the lipid composition of walnut kernel. According to the MS1 and MS2 data acquired in the positive and negative ion modes by electrospray ionization (ESI), a total of 525 lipids belonging to four classes were detected in walnut kernel, including 250 glycerolipids (GL), 221 glycerophospholipids (GP), 36 sphingolipids (SP) and 18 saccharolipids (SL), accounting for 87%, 12.97%, 0.02% and 0.01% of the total lipids, respectively. Diacylglycerols (DG) and triacylglycerols (TG) were the dominant glyceride components, accounting for 45.23% and 41.77% of the total lipids, respectively. TG (18:2/18:2/18:3) was the major TG and DG (18:2/18:2) was the major DG.?Essential fatty acids such as linoleic acid and linolenic acid were the major fatty acids in DG and TG. There were a variety of phospholipids in walnut kernel, including phosphatidic acid (PA), phosphatidylglycerol (PG), phosphatidyl serine (PS), phosphatidyl choline (PC), phosphatidyl ethanolamine (PE), phosphatidyl inositol (PI), phosphatidylinositol?diphosphate (PIP), lyso-posphatidyl choline (LPC), lyso-posphatidyl ethanolamine (LPE), lyso-phosphatidylglycerol (LPG), lyso-phosphatidyl inositol (LPI) and cardiolipin (CL). Among them, PA was the most predominant, accounting for 43.88%. The lipid profile constructed in this study can provide a theoretical basis for the functional development of walnut kernel and further research on its nutritional quality.

Key words: ultra-high performance liquid chromatography coupled to orbitrap high resolution mass spectrometry; walnut; lipidomics; functional lipids