Geometrical isomerisation of eicosapentaenoic and docosahexaenoic acid at high temperaturesConcentrates of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were heated at 140-240 7C for 2-8 h under nitrogen. The trans isomers were analysed by gas chromatography-mass spectrometry on a BPX-70 cyanopropyl column. All geometrical isomers of EPA and DHA with one trans double bond were observed. The rate constants (k) for the isomerisation of the all-cis isomers were calculated and found to be higher than previously reported for linoleic acid and a-linolenic acid. Arrhenius plots showed a linear relationship between ln k and the reciprocal absolute temperature above 180 7C. The distribution patterns of isomers with one trans double bond are approximately constant up to a degree of isomerisation of 25%. The degree of isomerisation can therefore be estimated from selected trans peaks.

The effect of activated carbon (AC) adsorption on the reduction of persistent organic pollutants (POP) in fish oil was studied based on response surface methodology at a 5-g/kg AC inclusion level. Pretreatment of the oil by alkali refining and bleaching increased the POP levels. The tested process variables (contact time and temperature) affected the AC adsorption rate and significant first-and second-order response models could be established. Polychlorinated dibenzo-pdioxins and dibenzofurans (PCDD/F) showed a very rapid adsorption behavior and the concentration and toxic equivalent (TEQ) level could be reduced by 99%. Adsorption of dioxin-like polychlorinated biphenyls (DL-PCB) was less effective and depended on ortho substitution, i.e. non-ortho PCB were adsorbed more effectively than mono-ortho PCB with a maximum of 87 and 21% reduction, respectively, corresponding to a DL-PCB-TEQ reduction of 73%. A common optimum for both PCDD/F and DL-PCB adsorption could not be identified. AC treatment had no effect on the level of polybrominated diphenyl ether flame retardants. The differences in adsorption patterns may be explained based on molecular conformation. No change in oil quality could be observed based on oxidation parameters. Compliance with present PCDD/F and DL-PCB legislation levels in fish oil can be achieved based on AC adsorption.

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