Abstract
To understand thecis-trans isomerization reaction of ethylenic bonds in heated octadecatrienoic acids (occurring during industrial deodorization of oils), we have prepared a mixture ofcis-9,cis-12,cis-15, andcis-9,cis-15 18:2 acids by partial hydrazine reduction ofcis-9,cis-12,cis-15 18:3 acid present in linseed oil. This mixture (as fatty acid methyl esters) was heated under vacuum at 270°C for 2.25 h. The two methylene-interrupted acids isomerize at a similar rate under such conditions, but the nonmethylene-interruptedcis-9,cis-15 18:2 acid remains unchanged. This means that the mechanism of isomerization does not involve a direct interaction between the two external ethylenic bonds as previously hypothesized. The centralcis-12 ethylenic bond is apparently necessary for the isomerization of the two externalcis-9 andcis-15 ethylenic bonds. However, this bond is itself rather protected against isomerization in the originalcis-9,cis-12,cis-15 18:3 acid which is mainly isomerized totrans-9,cis-12,trans-15,cis-9,cis-12,trans-15, andtrans-9,cis-12,cis-15 18:3 acids. Thecis-9,trans-12,cis-15 18:3 isomer is less than 10% of totaltrans isomers of α-linolenic acid. As a general rule, only one of the two double bonds in a methylene-interrupted diethylenic system can undergocis-trans isomerization when submitted to heat treatment, at least for temperatures equal to or less than 270°C.
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References
Ackman, R.G., S.N. Hooper, and D.L. Hooper, Linolenic Acid Artifacts from the Deodorization of Oils,J. Am. Oil Chem. Soc. 51:42–49 (1974).
Wolff, R.L., and J.-L. Sebedio, Geometrical Isomers of α-Linolenic Acid in Low-Calorie Spreads Marketed in France,68:719–725 (1991).
Wolff, R.L.,Trans-Polyunsaturated Fatty Acids in French Edible Rapeseed and Soybean Oils,,69:106–110 (1992).
Wolff, R.L., Further Studies on Artificial Geometrical Isomers of α-Linolenic Acid in Edible Linolenic Acid-Containing Oils,70:219–224 (1993).
Wolff, R.L., Occurrence of Artificialtrans-Polyunsaturated Fatty Acids in Refined (deodorized) Walnut Oils,Sci. Alim. 13:155–163 (1993).
O’Keefe, S., S. Gaskins-Wright, V. Wiley, and I.C. Chen, Levels oftrans Geometrical Isomers of Essential Fatty Acids in Some Unhydrogenated U.S. Vegetable Oils,J. Food Lipids 1:165–176 (1994).
Wolff, R.L., Heat-Induced Geometrical Isomerization of α-Linolenic Acid: Effect of Temperature and Heating Time on the Apperance of Individual Isomers,J. Am. Oil Chem. Soc. 70:425–430 (1993).
O’Keefe, S.F., V.A. Wiley, and D. Wright, Effect of Temperature on Linolenic Acid Loss and 18:3 Δ9-cis, Δ12-cis, Δ15-trans Formation in Soybean Oil,70:915 (1993).
Wolff, R.L., and J.-L. Sebedio, Characterization of γ-Linolenic Acid Geometrical Isomers in Borage Oil Subjected to Heat Treatments (deodorization),71:117 (1994).
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,71:1129–1134 (1994).
Ratnayake, W.M.N., Studies on Fatty Acids from Nova Scotian Seaweeds and on the Specificity of Hydrazine Reduction of Unsaturated Fatty Acids, Ph. D. Thesis, University of Dalhousie, Halifax, Canada, 1981.
Conway, J., W.M.N. Ratnayake, and R.G. Ackman, Hydrazine Reduction in the Gas-Liquid Chromatographic Analysis of the Methyl Esters of Cyclopropenoic Fatty Acids,J. Am. Oil Chem. Soc. 62:1340 (1985).
Wolff, R.L., Resolution of Linolenic Acid Geometrical Isomers by Gas-Liquid Chromatography on a Capillary Column Coated with 100% Cyanopropyl Polysiloxane Stationary Film (CPTMSil 88).J. Chromatogr. Sci., 30:17 (1992).
Ackman, R.G., The Analysis of Fatty Acids and Related Materials by Gas-Liquid Chromatography,Prog. Chem. Fats other Lipids 12:167–284 (1972).
Sebedio, J.-L., and R.G. Ackman, Calculation of GLC Retention Data for Some Accessible C20 Isomericcis-Unsaturated Fatty Acids,J. Chromatogr. Sci. 20:231–234 (1982).
Sebedio, J.-L., A. Grandgirard, and J. Prevost,J. Am. Oil Chem. Soc. 65:362–366 (1988).
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Wolff, R.L., Nour, M. & Bayard, C.C. Participation of thecis-12 ethylenic bond tocis-trans isomerization of thecis-9 andcis-15 ethylenic bonds in heated α-linolenic acid. J Am Oil Chem Soc 73, 327–332 (1996). https://doi.org/10.1007/BF02523426
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DOI: https://doi.org/10.1007/BF02523426