Docosahexaenoic Acid is More Stable to Oxidation when Located at the sn‐2 Position of Triacylglycerol Compared to sn‐1(3)

Abstract

Regio-isomeric effects on the oxidative stability of triacylglycerols (TAG) containing docosahexaenoic acid (DHA) were investigated using two pairs of regio-isomerically pure TAG, namely 1,3-dihexadecanoyl-2-(4,7,10,13,16,19-docosahexaenoyl)glycerol (PDP)/1,2-dihexadecanoyl-3-(4,7,10,13,16,19-docosahexaenoyl)glycerol (PPD) and 1,3-dioctadecenoyl-2-(4,7,10,13,16,19-docosahexaenoyl)glycerol (ODO)/1,2-dioctadecenoyl-3-(4,7,10,13, 16,19-docosahexaenoyl)glycerol (OOD) where P, O, and D represent palmitic acid, oleic acid, and DHA respectively. Each pair of regio-isomers was subjected to accelerated auto-oxidation (at 40 or 50°C inside a dark oven). In each case, the TAG oxidized more slowly when DHA was located at the sn-2 position (PDP and ODO) compared to the sn-1(3) position (PPD and OOD), as evidenced by slower development of peroxide value, slower depletion of DHA, and slower generation of secondary oxidation products propanal and trans, trans-2,4-heptadienal. The positional effect on auto-oxidation was more pronounced when DHA occurred in combination with oleic acid than with palmitic acid.

Oxidation progress in an emulsion made from metmyoglobin and different triacylglycerols

“…The peroxide values, determined for both oils, indicated a relatively low degree of initial oxidation. The most prominent volatile degradation products from the pure PUFA TAG systems were aldehydes, alcohols, ketones and furans, correlating relatively well with other studies (Frankel, 2005;Miyashita, 2008;Wijesundera et al, 2008). Hexanal, the common marker for n-6 PUFA, dominated the headspace of tri-LIN and tri-ARA.…”

“…Trioctanoin was chosen as a matrix in which to dissolve pure PUFA triacylglycerol, as studies have shown that the saturated species do not participate in lipid oxidation (Undeland, Hultin, & Richards, 2002), and also because these are fluid at room temperature. The rationale for choosing glycerol equivalents with three similar side-chains was to avoid the potential complexity of systems containing di or monoglycerides in which the exact position of the unsaturated chain cannot be guaranteed (Wijesundera et al, 2008). Obviously the free fatty acids (FFAs) could have been chosen but, as PUFAs in natural systems are more frequently in the form of TAGs, the latter were selected.…”

Perspectives on the membrane fatty acid unsaturation/pacemaker hypotheses of metabolism and aging

“…Moreover, the relative peroxidizabilities of free fatty acids may not always be relevant to how they act as acyl groups when attached to larger molecules (Cosgrove et al, 1987;Kubo et al, 2005;Norris et al, 2012;Wijesundera et al, 2008;Zerouga et al, 1995). For instance, phospholipids containing two DHA groups were peroxidized at the similar rates or sometimes a lower rate than phospholipids containing a DHA and a palmitic acyl group when put into liposomes composed of phospholipids with saturated fatty acyl groups, contrary to what would be predicted based on the peroxidizability indexes (Norris et al, 2012).…”

Long‐chain omega‐3 oils: Current and future supplies, food and feed applications, and stability

“…Using combined chemical and enzymatic techniques, we synthesized pairs of regioisomerically pure TAG isomers containing DHA in combination with palmitic or oleic acids for oxidation and bioactivity experiments [4]. We subjected each pair of isomers to accelerated oxidation and established that DHA is more resistant to oxidation when sn-2 located (Figure 1) [5]. These observations encourage genetic engineers to pay attention to LC omega-3 location when designing future landbased LC omega-3 crops.…”