High-performance liquid chromatography–atmospheric pressure chemical ionization mass spectrometry and gas chromatography–flame ionization detection characterization of Δ5-polyenoic fatty acids in triacylglycerols from conifer seed oils

Edible conifer seeds can serve as a source of triacylglycerols (TGs) with unusual Δ5 unsaturated polymethylene interrupted fatty acids (UPIFAs), such as cis-5,9-octadecadienoic (taxoleic), cis-5,9,12-octadecatrienoic (pinolenic), cis-5,11-eicosadienoic (keteleeronic) and cis-5,11,14-eicosatrienoic acids (sciadonic). Conifer seed oils from European Larch (Larix decidua), Norway Spruce (Picea abies) and European Silver Fir (Abies alba) have been analyzed by non-aqueous reversed-phase high-performance liquid chromatography (NARP-HPLC) with atmospheric pressure chemical ionisation (APCI)-MS detection. The influence of different positions of double bonds in Δ5-UPIFAs on the retention and fragmentation behavior is described and used for the successful identification of TGs in each oil. TGs containing Δ5-UPIFAs have a higher retention in comparison with common TGs found in plant oils with single methylene interrupted Δ6(9)-FAs and also significantly changed relative abundances of fragment ions in APCI mass spectra. Results obtained from HPLC/MS analyses are supported by validated GC/FID analyses of fatty acid methyl esters after the transesterification. The total content of Δ5-UPIFAs is about 32% for European Larch, 27% for Norway Spruce and 20% for European Silver Fir. In total, 20 FAs with acyl chain lengths from 16 to 24 carbon atoms and from 0 to 3 double bonds have been identified in 64 triacylglycerols from 3 conifer seed oils.