Characterization of volatile compounds and triacylglycerol profiles of nut oils using SPME-GC-MS and MALDI-TOF-MS

Several nut oil varieties mainly used as culinary and overall healthy food ingredients were subject of the present study. Headspace solid-phase microextraction combined with gas chromatography-mass spectrometry was employed in order to determine the qualitative composition of volatile compounds. Furthermore, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used in order to assess the profiles and relative composition of the prevalent triacylglycerols (TAG) within the oils. The headspace of the majority of oil samples was dominated by high contents of acetic acid (up to 42%) and hexanal (up to 32%). As nut oils are typically gained by cold-pressing from previously roasted nuts, characteristic pyrazine derivatives as well as degradation products of long-chain fatty acids were detected. TAG analysis of these oils revealed a quite homogeneous composition dominated by components of the C-52 and C-54 group composed mainly of oleic (18: 1), linoleic (18:2), stearic (18:0) and palmitic (16:0) acid residues representing together between 65 and 95% of the investigated nut oils. The TAG profiles showed characteristic patterns which can be used as 'fingerprints' of the genuine oils. Nut oils exhibiting quite similar fatty acid composition (e.g. hazelnut, pistachio and beech oil) could be clearly discriminated based on TAG showing significant differences between the oils.