Direct Analysis of Triterpenes from High-Salt Fermented Cucumbers Using Infrared Matrix-Assisted Laser Desorption Electrospray Ionization (IR-MALDESI) |
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| Authors: | Måns Ekelöf Erin K. McMurtrie Milad Nazari Suzanne D. Johanningsmeier David C. Muddiman |
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| Affiliation: | 1.W. M. Keck FTMS Laboratory for Human Health Research, Department of Chemistry,North Carolina State University,Raleigh,USA;2.Department of Food, Bioprocessing, and Nutrition Sciences,North Carolina State University,Raleigh,USA;3.Food Science Research Unit,USDA Agricultural Research Service,Raleigh,USA |
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| Abstract: | High-salt samples present a challenge to mass spectrometry (MS) analysis, particularly when electrospray ionization (ESI) is used, requiring extensive sample preparation steps such as desalting, extraction, and purification. In this study, infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) coupled to a Q Exactive Plus mass spectrometer was used to directly analyze 50-μm thick slices of cucumber fermented and stored in 1 M sodium chloride brine. From the several hundred unique substances observed, three triterpenoid lipids produced by cucumbers, β-sitosterol, stigmasterol, and lupeol, were putatively identified based on exact mass and selected for structural analysis. The spatial distribution of the lipids were imaged, and the putative assignments were confirmed by tandem mass spectrometry performed directly on the same cucumber, demonstrating the capacity of the technique to deliver confident identifications from highly complex samples in molar concentrations of salt without the need for sample preparation. |
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