Original Article


, Volume 47, Issue 7, pp 659-667

First online:

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

  • Caterina SciottoAffiliated withDepartment of Chemistry, University of BergenDipartimento Farmaco-chimico, Facoltà di Farmacia, Università di Messina
  • , Svein A. MjøsAffiliated withDepartment of Chemistry, University of BergenNofima BioLab Email author 

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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