, Volume 47, Issue 7, pp 659–667 | Cite as

Trans Isomers of EPA and DHA in Omega-3 Products on the European Market

Original Article


The levels of trans isomers of eicosapentaenoic (EPA) acid and docosahexaenoic acid (DHA) in 77 omega-3 products on the European market have been studied. Fatty acids were analyzed as fatty acid methyl esters by gas chromatography with a flame ionization detector, using a cyanopropyl coated stationary phase. The amount of mono-trans EPA isomers relative to the corresponding all-cis isomer ranged from 0.19 to 4.5 %. The corresponding values for mono-trans DHA relative to the all-cis isomer ranged from 0.25 to 5.9 %. There was a strong correlation between the degree of isomerization of EPA and DHA, showing that DHA was 1.26 times more isomerized than EPA. Division of the samples into different product groups showed that samples with a low degree of isomerization were found in all groups, except one. This shows that a high degree of isomerization is avoidable, and also points to deodorization of the oils as the main source of trans isomers.


Omega-3 supplements Fish oil Fish oil concentrates EPA DHA Trans fatty acids Thermal isomerization 



Alpha linolenic acid (18:3n-3)


Docosahexaenoic acid (22:6n-3)


Docosapentaenoic acid (22:5n-3)


Degree of isomerization


Eicosapentaenoic acid (20:5n-3)


Fatty acid methyl ester


Gas chromatography


Mass spectrometry

Supplementary material

11745_2012_3672_MOESM1_ESM.pdf (35 kb)
Supplementary material 1 (PDF 35 kb)


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Copyright information

© AOCS 2012

Authors and Affiliations

  1. 1.Department of ChemistryUniversity of BergenBergenNorway
  2. 2.Dipartimento Farmaco-chimico, Facoltà di FarmaciaUniversità di MessinaMessinaItaly
  3. 3.Nofima BioLabFyllingsdalenNorway

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