Trans isomers of EPA and DHA in refining and concentration of fish oils.

Abstract

The omega-3 long-chain polyunsaturated fatty acids (LC-PUFA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are strongly recommended to be part of a normal diet due to the many positive health effects in humans. Health authorities in many countries recommend an average daily intake of 0.25 – 0.5 grams of EPA and DHA by eating fish at least twice a week or alternatively, consume fish oil supplements. The unsaturated fatty acids in native marine and vegetable lipids are all present as cis-isomers while trans-isomers are found in industrially hydrogenated oils and in minor amounts in fat from ruminants. The intake of large amounts of trans-fatty acids is considered to have serious negative health effects and the advices are to reduce the consumption as much as possible. Several processing steps are necessary to produce high quality fish oil supplements, including concentrated forms of EPA and DHA. These steps include high temperature processes that might induce transformation of cis-double bonds to trans-double bonds in the unsaturated fatty acids. The objectives of this thesis was determine if the processing conditions used at Nordic Pharma Inc. resulted in the formation of trans fatty acids in both natural “1812” fish oils (18 % EPA, 12 % DHA) and EPA/DHA concentrates and to investigate how time and temperature used in the processing steps affected the formation of trans fatty acids in fish oil concentrates. Initially, a method for the analysis of trans fatty acids in fish oils was established. Methylated standards of trans EPA and DHA were produced using p-toluenesulfinic acid as catalyst and separating the different isomers on high performance thin layer chromatography (HPTLC) plates impregnated with silver nitrate. A 100 meter SLB-IL111, the most polar gas chromatography (GC) column commercially available, was used to analyze the samples. The preparation and the separation of the trans standards on HPTLC plates was successful and gave sufficient amounts to optimize a temperature program for GC separation. The results from samples of processed fish oil showed that only minor amounts of trans fatty acids were formed during the processing conditions applied at Nordic Pharma Inc. The content of trans fatty acids was far below the amount allowed for such products. The SLB-IL111 column worked well as a tool for analysis of trans fatty acids in fish oil, but some further investigations are needed for this analysis system to be optimized. The temperature experiment showed that 200 °C for more than an hour was needed for the formation of larger amounts of trans LC-PUFA to occur.

Keywords: Fish oil, industrial processing, trans fatty acids, EPA, DHA, SLB-IL111, silver ion TLC