title: Direct Analysis of Triterpenes from High-Salt Fermented Cucumbers Using Infrared Matrix-Assisted Laser Desorption Electrospray Ionization (IR-MALDESI).
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. Graphical Abstract ᅟ.
authors.affiliation: W. M. Keck FTMS Laboratory for Human Health Research, Department of Chemistry, North Carolina State University, Raleigh, NC, 27695, USA.
authors.forename: Måns
authors.initials: M
authors.lastname: Ekelöf
authors.affiliation: Department of Food, Bioprocessing, and Nutrition Sciences, North Carolina State University, Raleigh, NC, 27695, USA.
authors.forename: Erin K
authors.initials: EK
authors.lastname: McMurtrie
authors.affiliation: W. M. Keck FTMS Laboratory for Human Health Research, Department of Chemistry, North Carolina State University, Raleigh, NC, 27695, USA.
authors.forename: Milad
authors.initials: M
authors.lastname: Nazari
authors.affiliation: Department of Food, Bioprocessing, and Nutrition Sciences, North Carolina State University, Raleigh, NC, 27695, USA.|Food Science Research Unit, USDA Agricultural Research Service, Raleigh, NC, 27695, USA.
authors.forename: Suzanne D
authors.initials: SD
authors.lastname: Johanningsmeier
authors.affiliation: W. M. Keck FTMS Laboratory for Human Health Research, Department of Chemistry, North Carolina State University, Raleigh, NC, 27695, USA. david_muddiman@ncsu.edu.
authors.forename: David C
authors.initials: DC
authors.lastname: Muddiman
mesh_terms: D018553:Cucumis sativus / Q000737:chemistry*; D000074421:Fermented Foods / Q000032:analysis*; D005504:Food Analysis / Q000379:methods*; D061353:Food Storage / Q000379:methods; D007091:Image Processing, Computer-Assisted; D012965:Sodium Chloride; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry; D014315:Triterpenes / Q000032:analysis* / Q000737:chemistry
chemical_list: D014315:Triterpenes; D012965:Sodium Chloride
keywords: Direct analysis; Fermented vegetable composition; Food preservation; HRAM; IR-MALDESI; Mass spectrometry imaging; Phytosterols; Q Exactive