High-Resolution Electrospray-Ionization Fourier-Transform Ion Cyclotron Resonance and Gas Chromatography–Mass Spectrometry of Macadamia Nut Oil

Abstract

An oil sample from macadamia nuts is examined using electrospray-ionization (ESI) Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS) and gas chromatography–mass spectrometry (GC-MS). The neat oil, the methanol extract of the oil, the esterified oil, and the esterified methanol extract of the oil are examined using these two techniques. Various acylglycerols and fatty acids are identified using the high-resolution exact mass and elemental analysis routines. High performance liquid chromatography is also used for separation and collection of oil-extract fractions, prior to the mass spectrometry studies, to identify various molecular isomers of compounds in the nut oil. A comparison of the results from GC-MS experiments on the esterified oil and methanol extract of the oil with those from the FTICR-MS experiments reveals that the latter technique provides more detailed information on the composition of the macadamia oil including a relative concentration profile for the free fatty acids present in the oil. We observe the presence of fatty acids and acylglycerides containing one or more additional oxygen atoms, which may be in the form of peroxy, hydroperoxy, oxo (ketone or aldehyde functionalities), hydroxy, and/or epoxy substituents as well as a number of unusual free fatty acids and mono- and di-acylglycerides containing an odd number of carbon atoms. The simplicity of the sample preparation when combined with the results from the high resolution, high mass accuracy ESI-FTICR-MS experiments on the macadamia nut oil indicate that this method is a powerful tool that can be used for the analysis of trace compounds in animal and plant oils.