Spatial lipidomics of eight edible nuts by desorption electrospray ionization with ion mobility mass spectrometry imaging

Nuts have long been known for their health benefits which are mainly contributed by their lipid components. However, the spatial distribution of lipids in nuts has not been firmly established. In this study, desorption electrospray ionization combined with ion mobility and quadrupole time-of-flight mass spectrometry in positive and negative ion modes was applied to visualize spatially the lipids in eight edible nuts, namely almonds, hazelnuts, cashews, walnuts, peanuts, peach seeds, bitter almonds, and Chinese dwarf cherry seeds. The glycerophospholipids were first imaged in nuts in the negative ion mode, while the glycerolipids and phosphatidylcholines were mainly detected in the positive ion mode. In total 87 characterized components, including 47 glycerophospholipids, 24 glycerolipids, eight alkyl phenolic acids, three fatty acid acyl metabolites, four oligosaccharides, and amygdalin, were visualized in the eight nuts, and the collision cross-sectional values of these components were obtained. The outer shell of the nut cotyledon concentrated more abundant components than the center, while for the hydrolyzed glycerophospholipids, the reverse was observed. The results provide a more comprehensive and in-depth understanding of the location of the diverse metabolite profiles in nuts and of their relationship to their respective health benefits.