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Omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are essential for human health but prone to oxidation. While esterification location is known to influence the stability of omega-3 in triacylglycerols (TAGs) in oxidation trials, their oxidative behavior in the gastrointestinal tract is unknown. Synthesized ABA- and AAB-type TAGs containing DHA and EPA were submitted to static in vitro digestion for the first time. Tridocosahexaenoin and DHA as ethyl esters were similarly digested. Digesta were analyzed by gas chromatography, liquid chromatography–mass spectrometry, and nuclear magnetic resonance spectroscopy. Besides the formation of di- and monoacylglycerols, degradation of hydroperoxides was detected in ABA- and AAB-type TAGs, whereas oxygenated species increased in tridocosahexaenoin. Ethyl esters were mainly unaffected. EPA was expectedly less susceptible to oxidation prior to and during the digestion process, particularly in sn-2. These results are relevant for the production of tailored omega-3 structures to be used as supplements or ingredients.

The dietary intake of marine foods is globally inadequate, and thus supplements with long-chain omega-3 fatty acids are widely used. Both the source and processing choices affect the lipid class (most typically triacylglycerols (TAGs), ethyl esters (EEs), or phospholipids (PLs)) in which docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are present, and thus consumed.Here we present investigation of the effect of lipid type on oxidation by the analysis of oxidation products of commercial supplements including EPA and DHA in different lipid forms, as well as results of an oxidation trial of pure DHA-containing TAGs and EEs in the presence and absence of alpha-tocopherol. We also present the applicability of SPME-GC-MS and NMR methods as well as analysis of the loss of antioxidants as alternative methods to peroxide (PV) and para-anisidine values (PAV). PAV typically has challenges with aroma compounds present and the reliability of PV is decreased by different formation and decomposition rates of hydroperoxides under different conditionsIncreased lipid oxidation was detected in 24% of the studied omega-3 supplements, which were in either TAG or EE form. 1H NMR was found to be a potential rapid method for lipid class determination and was applicable in detecting products of oxidation through selective pulse experiments. Analysis of volatile secondary oxidation products with SPME-GC-MS may be a future alternative to PAV analysis of especially flavored products when standardized. 2,4-Heptadienal, 1-penten-3-ol, and 2-hexenal showed the highest potential to be used as indicator compounds for lipid oxidation in products high in EPA and DHA content. Oxidative stability, oxidation pattern, and α-tocopherol response of DHA were influenced by the lipid structure (TAG/EE). DHA in EE form was found to be more stable than DHA in TAG form in the presence of α-tocopherol, but the opposite was observed without the antioxidant.