Positional distribution of Δ5‐acids in triacylglycerols from conifer seeds as determined by partial chemical cleavage

Abstract

The positional distribution of various ∆5-acids in the seed triacylglycerols from several conifer species has been established after partial chemical degradation with Grignard reagent. The species studied were representative of four conifer families and were specially selected for their particularly high ∆5-acid contents. These species were Taxus baccata (Taxaceae; 5,9-18:2 acid, 11.9%), Larix decidua (Pinaceae; 5,9,12-18:3 acid, 28.5%), Sciadopytis verticillata (Taxodiaceae; 5,11,14-20:3 acid, 16.7%), and Juniperus communis (Cupressaceae;5,11,14,(17)(18)(19)(20) 19.8%). Calculations from the fatty acid compositions of triacylglycerols and of the mixture of 1,2-and 2,3-diacylglycerols generated by the Grignard reagent indicated that, for the four species, there was a considerable enrichment of ∆5-acids (generally more than ten times) in the 1,3-positions as compared to the 2-position, where ∆5-acids represented always less than 2% of total fatty acids esterified to triacylglycerols. This distribution was practically independent from the species (four families studied), the chainlength (18 or 20 carbon atoms), and the number of ethylenic bonds (two to four) in the ∆5-acids. Similar distributions were established for triacylglycerols from the seeds of three pine species that are available on a ton-scale: Pinus pinea, P. koraiensis, and P. pinaster. These observations confirm and extend previous studies conducted with other conifer species by similar techniques or by 13 C-nuclear magnetic resonance spectroscopy. Consequently, the almost exclusive location of ∆5-acids in the external positions of triacylglycerols is now well established and appears to be a general feature of conifer seed oils. JAOCS 74, 165-168 (1997). KEY WORDS:Conifer seed oils, ∆5-acids, positional distribution, triacylglycerols.In the search for ∆5-acids, some of which have structures closely related to those of arachidonic and eicosapentaenoic acids, and following a systematic study of conifer seed oils (1,2), four species could be selected with a high content of one of the following ∆5-acids: 5, 9-18:2, 5,9,12-18:3, 5,11,14-20:3, and 5,11,14,17-20:4 acids (double bonds in the cis configuration). These species were Taxus baccata, Larix decidua, Sciadopytis verticillata, and Juniperus communis, respectively. Moreover, each of these species is representative of one of the four conifer families, Taxaceae, Pinaceae, Taxodiaceae, and Cupressaceae, respectively. A biosynthetic pathway for these acids has recently been proposed (2), based on a ∆5-desaturase activity upon 9-18:1, 9,12-18:2, 11,14-20:2, and 11,14,17-20:3 acids as substrates.Previous 13 C-nuclear magnetic resonance (NMR) spectroscopy investigations (3,4) have shown that ∆5-acids were present in the external positions of triacylglycerols (TAG) from the seeds of all species analyzed, with apparently no ∆5-acids in the 2-position, at least within the limits of the technique (∆5-acids in amounts less than 3% could not be detected). These observations were in general agreement with those of T...

Effects of Δ5 polyunsaturated fatty acids of maritime pine (Pinus pinaster) seed oil on the fatty acid profile of the developing brain of rats

“…The ∆5 PMI-PUFA, particularly 5,9,12-18:3 and 5,11,14-20:3, because of their structural similarity to n-6 PUFA, should also be concentrated in the sn-3 position of milk TAG and, consequently, preferentially cleaved and well absorbed. It is necessary to study the ∆5 PMI-PUFA distribution in milk TAG to confirm the site of esterification as the sn-3 position, as was reported for conifer seed oil TAG structure (21).…”

Arachidonic, eicosapentaenoic, and biosynthetically related fatty acids in the seed lipids from a primitive gymnosperm, Agathis robusta

“…In addition to their peculiar structures, ∆5-UPIFA also show a strong tendency to be almost exclusively esterified to the α positions of triacylglycerols (TAG), likely the sn-3 position, which leads to high proportions of TAG with only one ∆5-UPIFA per molecule (13,14,18,(30)(31)(32)(33)(34)(35). Besides these aspects relevant to chemistry and biochemistry, ∆5-UPIFA in combination with other common fatty acids have been used as interesting chemometric markers for the taxonomy of conifers (3)(4)(5)(6).…”

The seed fatty acid composition and the distribution of Δ5‐olefinic acids in the triacylglycerols of some taxaceae (Taxus and Torreya)

“…Those from T. cuspidata (Japanese yew) and T. canadensis (Canadian yew) were described later by Takagi and Itabashi (4,5). Some precision has been added more recently for T. baccata seed fatty acids and triacylglycerol (TAG) structure by Wolff et al (6)(7)(8) and Gunstone et al (9).…”