Abstract
To understand the heat-inducedcis-trans isomerization of ethylenic bonds in octadecatrienoic acids, pine seed oil, which contains the unusual nonmethylene-interrupted pinolenic (cis-5,cis-9,cis-12 18∶3) acid as a major component, was heated under vacuum at 240°C for 6 h together with linseed and borage oils. As a results, a small percentage of pinolenic acid undergoescis-trans isomerization. The main isomer that accumulates is thetrans-5,cis-9,trans-12 18∶3 acid. Minor amounts of the three mono-trans isomers are also present. Identification of isomers was realized by combining gas-liquid chromatography on a CP Sil 88 capillary column, argentation thin-layer chromatography and comparing the equivalent chainlengths of artifacts to those of isomers present in NO2-isomerized pine seed oil. Hydrazine reduction was used to demonstrate that there was no positional shift of double bonds. Heat-induced geometrical isomerization of pinolenic acid differs from that of α- and γ-linolenic acids in at least two aspects. The reaction rate is slower (about one-fourth), and mono-trans isomers are formed in low amounts.
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Wolff, R.L. Cis-trans isomerization of octadecatrienoic acids during heating. Study of pinolenic (cis-5,cis-9,cis-12 18∶3) acid geometrical isomers in heated pine seed oil. J Am Oil Chem Soc 71, 1129–1134 (1994). https://doi.org/10.1007/BF02675907
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DOI: https://doi.org/10.1007/BF02675907