Regiospecific analysis of conifer seed triacylglycerols by gas-liquid chromatography with particular emphasis on Δ5-olefinic acids

Dibutyroyl derivatives of monoacylglycerols (DBMAG) from conifer seed oil triacylglycerols (TAG) were prepared by partial deacylation of TAG with ethylmagnesium bromide followed by diesterification with n-butyryl chloride. The resulting mixtures were analyzed by gas-liquid chromatography (GCL) with 65% phenylmethyl silicon open tubular fused-silica capillary column operated under optimal conditions and separated according to both their fatty acid structures and their regiospecific distribution. Seed oils of 18 species from 5 conifer families (Pinaceae, Taxaceae, Cupressaceae, Cephalotaxaceae, and Podocarpaceae) were analyzed. The chromatograms showed a satisfactory resolution of DBMAG containing palmitic (16∶0) stearic (18∶0), taxoleic (cis-5, cis-9 18∶2), oleic (cis-9 18∶1), cis-vaccenic (cis-11 18∶1), pinolenic (cis-5, cis-9, cis-12 18∶3), linoleic (cis-9, cis-12 18∶2), α-linolenic (cis-9 cis-12, cis-15 18∶3), and an almost baseline resolution of DBMAG containing gondoic (cis-11 20∶1), cis-5, cis-11 20∶2, sciadonic (cis-5, cis-11, cis-14 20∶3), dihomolinoleic (cis-11 cis-14 20∶2), juniperonic (cis-5, cis-11, cis-14, cis-17 20∶4), and dihomo-α-linolenic (cis-11, cis-14, cis-17 20∶3) acids. We have observed that results for Pinus pinaster and P. koraiensis seed oils obtained with this new simple method compared favorably with literature data established with other usual regiospecific analytical techniques. Δ5-Olefinic acids are esterified mainly at the external positions of the glycerol backbone in all cases, in agreement with data obtained by other methodologies allowing validation of the GLC regiospecific method. To date, 45 gymnosperm species (mostly Coniferophytes) from 21 genera belonging to 9 families have been analyzed, all of them showing a definite enrichment of Δ5-olefinic acids in the external positions of TAG. These fatty acids (FA), with one exception only, represent between-2 and 8% of FA esterified to the internal positions. For some species, i.e., P. koraiensis and P. pinaster, this asymmetrical distribution was established by at least three analytical procedures and confirmed by stereospecific analysis of their seed TAG.