Polyunsaturated lipids and vitamin A oxidation during cod liver oil in vitro gastrointestinal digestion. Antioxidant effect of added BHT

•Hydrolysis and oxidation of cod liver oil during in vitro digestion were studied.•For the first time, monoepoxides and 4-hydroperoxy-trans-2-alkenals were detected.•Vitamin A naturally present in cod liver oil was greatly oxidized during digestion.•BHT added at 20 ppm limited oxidation, and at 800 ppm almost totally inhibited it.

The extent of cod liver oil hydrolysis and oxidation during in vitro gastrointestinal digestion was investigated by Proton Nuclear Magnetic Resonance (1H NMR) and Solid Phase Microextraction-Gas Chromatography/Mass Spectrometry (SPME-GC/MS). These techniques evidenced the degradation of polyunsaturated ω-3 and ω-6 lipids and, for the first time, that of vitamin A, naturally present in cod liver oil. Cis,trans-conjugated dienes associated with hydroperoxides, as well as monoepoxides, cis,trans-2,4-alkadienals, 4-hydroperoxy- and 4-hydroxy-2-alkenals, and several vitamin A derived metabolites were generated. Moreover, the effect of the addition of the synthetic antioxidant 2,6-di-tert-butyl-hydroxytoluene (BHT) at 20 and 800 ppm was tackled. Both techniques showed BHT to be efficient in limiting oxidation reactions during digestion, almost inhibiting them at 800 ppm. Therefore, the simultaneous intake of antioxidants with cod liver oil should be considered, in order to increase polyunsaturated lipid and vitamin A bioaccessibility and avoid formation of toxic oxidation compounds like oxygenated alpha,beta-unsaturated aldehydes.