Synergistic Antioxidant Activity of Milk Sphingomyeline and Its Sphingoid Base with α-Tocopherol on Fish Oil Triacylglycerol

Abstract

The effects of milk phospholipids (PLs), sphingolipids (SLs), and their sphingoid backbone on the oxidation of fish oil triacylglycerol (TAG) were examined with or without α-tocopherol. All compounds had little effect on the TAG oxidation in the absence of α-tocopherol. On the other hand, they could act synergistically with α-tocopherol. The highest synergistic activity was shown by sphingoid bases, followed by sphingomyelin (SPM) and other amine-containing PLs and SLs. This result showed that the synergistic activity increased with an increasing concentration of amine group of PLs, SLs, or sphingoid bases in the reaction mixture. The comparison of changes in α-tocopherol content in fish oil TAG and tricaprylin suggested that antioxidant compounds would be formed from the amine group and the lipid oxidation products in a mild oxidation condition controlled by α-tocopherol.

Inhibitory Effect of Dihydrosphingosine with α-Tocopherol on Volatile Formation during the Autoxidation of Polyunsaturated Triacylglycerols

“…On the other hand, no antioxidant activity was found in the addition of d18:0 to TAG without α-tocopherol in the present study Fig. 3 and our former study 10 . Therefore, the formation of antioxidant com- The stability was analyzed by measuring the decrease in oxygen A and the increase in total volatiles B in the headspace gas of the vial.…”

“…The addition of 1.0 wt d18:0 with 0.05 wt α-tocopherol effectively inhibited the oxygen absorption and peroxide formation during the fish oil TAG oxidation for more than 500 h, whereas a rapid increase in both oxidation indicators was found with the addition of α-tocopherol alone. This result suggests the possible application of d18:0 and tocopherol combination to prevent fish oil oxidation; however, EPA-and DHA-hydroperoxides are easily decomposed into volatile secondary oxidation products; then, it is possible for fish oils to have an undesirable flavors and tastes, even with low peroxide levels, as found in the former study 10 .…”

“…This result suggests the formation of antioxidant compounds during the first stage of the fish oil TAG incubation. On the other hand, α-tocopherol linearly decreased in non-oxidized tricaprylin mixture in the presence of α-tocopherol, though the tricaprylin substrate mixture contained the same amount of d18:0 and α-tocopherol as that found in fish oil TAG 10 .…”

“…Although the structures of the antioxidant compounds have not been made clear, they could effectively inhibit the fish oil TAG oxidation as following mechanisms: a regeneration of α-tocopherol to inhibit the lipid oxidation; b direct inhibition of lipid oxidation; c a and b . When d18:0 was added to fish oil TAG in the presence of α-tocopherol, a little decrease in the tocopherol level and a little oxidation of TAG were observed at the first stage of the incubation, but thereafter, there were no change in the tocopherol and no TAG oxidation 10 . This result suggests the formation of antioxidant compounds during the first stage of the fish oil TAG incubation.…”

“…Tocopherols can be more active when used in combination with other antioxidants, such as citric acid and ascorbic acid. Amine-containing phospholipids and sphingolipids have also been reported to effectively inhibit the oxidation of PUFA in the presence of α-tocopherol, whereas little antioxidant activity was found in these polar lipids without α-tocopherol 9,10 . Moreover, we have found stronger antioxidant activity of sphingoid base, dihydrosphingosine d18:0 , with α-tocopherol on fish oil triacylglycerol TAG oxidation 10 Fig.…”