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Research Project: Improved Processes for the Preservation and Utilization of Vegetables, Including Cucumber, Sweetpotato, Cabbage, and Peppers to Produce Safe, High Quality Products with Reduced Energy Use and Waste

Location: Food Science Research

Title: Direct analysis of triterpenes from high-salt fermented cucumbers using infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI)

Author
item Ekelof, Maans - North Carolina State University
item Mcmurtrie, Erin - North Carolina State University
item Nazari, Milad - North Carolina State University
item Johanningsmeier, Suzanne
item Muddiman, David - North Carolina State University

Submitted to: Journal of American Society for Mass Spectrometry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2016
Publication Date: 2/1/2017
Publication URL: http://handle.nal.usda.gov/10113/5763070
Citation: Ekelof, M., McMurtrie, E., Nazari, M., Johanningsmeier, S.D., Muddiman, D.C. 2017. Direct analysis of triterpenes from high-salt fermented cucumbers using infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI). Journal of American Society for Mass Spectrometry. 28(2):370-375.

Interpretive Summary: A novel mass spectrometry imaging approach was applied to the direct analysis of fermented cucumbers that contained a high concentration of salt. From several hundred observed unique substances, three triterpenoid lipids produced by cucumbers; ß-sitosterol, stigmasterol, and lupeol, were identified, and the spatial distribution of the lipids in a slice of fermented cucumber were imaged. This study demonstrates the capacity of the infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) technique to deliver confident identifications from highly complex samples in molar concentrations of salt without the need for sample preparation.

Technical 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 1M sodium chloride brine. From the several hundred unique substances observed, three triterpenoid lipids produced by cucumbers, ß-sitosterol, stigmasterol, and lupeol, were putatively identified based on exactmass 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.