A great variety of dietary supplements rich in omega-3 lipids is available on the market. They differ not only in their composition in main components (acyl groups), but also in those minor ones, which often include compounds added as antioxidants. Although these differences among supplements can influence their oxidative stability, very little is known about their behaviour under oxidative conditions and the factors influencing it. Taking this into account, two non-encapsulated dietary supplements manufactured from fish oils, with very similar proportions of -3 (molar percentage around 33%) and also of other kinds of unsaturated groups, were selected: S1, richer in EPA, and S2, richer in DHA. The analysis of their minor component profiles by means of Direct Immersion Solid Phase Microextraction revealed that the concentrations of potentially antioxidant tocopherols were more elevated in S2, which unlike S1, also contained tocopherol acetate. Both supplements were submitted to accelerated storage conditions at mild temperature (45 ºC) in an oven during 114 days, and Proton Nuclear Magnetic Resonance was used to follow the evolution of DHA and EPA groups, together with the formation of certain oxidation products. Despite their similarity in unsaturation degree, both samples showed different evolutions during the oxidation process. Thus, although the generation of hydroperoxides (primary oxidation products) was faster and the level reached higher in S2 sample, the degradation extent of -3 groups after 60 days of storage was noticeably higher in S1 sample. Therefore, considering that a higher susceptibility to oxidation could be expected in S2 sample due to its higher DHA proportion, the results suggest that the minor components present in this supplement could have played a key role in its higher stability throughout time. These findings evidence the great importance of the selection of the minor components added to this kind of supplements in order to preserve their -3 group content.
Acknowledgements: This work has been supported by the Basque Government (EJ-GV IT1490-22). D.D. Weinbinder thanks for a predoctoral contract supported by the European Union-Next Generation EU through the Investigo Programme.