Headspace composition of cod liver oil and its evolution in storage after opening. First evidence of the presence of toxic aldehydes

The headspaces of two samples of cod liver oil, when recently acquired, after five and after fifteen months from opening, were studied by solid phase microextraction, followed by gas chromatography/mass spectrometry. Nearly one hundred compounds were found, some of them identified for the first time as cod liver oil components. In both samples, the presence of the toxic 4-hydroxy-(E)-2-hexenal and of 4-oxo-(E)-2-hexenal was detected, as well as that 4,5-epoxy-2-heptenal in one of the samples; this is the first time that these toxic compounds have been described as being present in cod liver oil. In the early oxidation stages, taking place during storage, the compounds formed are mainly of low molecular weight; some of these could be adopted as oxidation markers of cod liver oil. The possibilities of using the technique to evaluate the oxidation level of cod liver oil are shown. These results suggest the need to monitor the levels of toxic oxygenated α,β-unsaturated aldehydes in cod liver oil in order to ensure its safety.