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Lipid Oxidation and Quality

Session:: Fundamentals of Lipid Oxidation - Mechanisms

Oxidative stability of docosahexaenoic acid is affected by its enantiospecific location in triacylglycerols in the presence of chiral RRR-tocopherol

Monday, May 1, 2023
12:20 PM – 12:40 PM MDT
Room: 205
Abstract: Due to the lack of regio- or stereopure model compounds, the influence of the structural characteristics of triacylglycerols (TAG) on the oxidative stability of n−3 polyunsaturated fatty acids has mainly been studied by randomization of natural oils or non-enantiomerically pure synthetic TAGs. Thus prior to this study, the influence of docosahexaenoic acid’s (DHA) exact location (sn-1, sn-2, or sn-3), on TAG’s oxidative stability, especially in the presence of a chiral antioxidant, has been unclear.

This study compared the oxidative stability of DHA in regio- and enantiopure TAGs in the presence and absence of RRR-α-tocopherol. Regiopure symmetrically structured ABA-type (A = C16:0; B = DHA) TAG and regio- and enantiopure asymmetrically structured AAB-type [sn-1 = (S)-AAB and sn-3 = (R)- AAB] TAGs were synthesized. Headspace solid-phase micro-extraction with gas chromatography–mass spectrometry, liquid chromatography–mass spectrometry, and nuclear magnetic resonance spectroscopy were applied to study the oxidation product formation at 50 °C in the dark at different time points. Additionally, the fatty acid and α-tocopherol contents were followed.

DHA was most stable in the sn-2 position with or without added RRR-α-tocopherol based on primary and secondary oxidation product analysis and DHA depletion. This could be attributed to the interaction of acyl chains within the same TAG molecule and possible steric hindrance for hydroperoxide formation. Without RRR-α-tocopherol, the stability of DHA in sn-1 and sn-3 positions was mainly similar as expected due to non-chiral environment. With RRR-α-tocopherol, significantly higher stability of DHA in sn-1 compared to sn-3 was observed. This suggests increased antioxidant response due to diastereomeric interactions between RRR-α-tocopherol and DHA in sn-1 position. The obtained results are especially relevant for enzymatic restructuring processes of DHA-rich fish or microalgae oil concentrates aimed for food supplements or food fortification.