Oxidative stability of docosahexaenoic acid-containing oils in the form of phospholipids, triacylglycerols, and ethyl esters

The peroxidative stability of docosahexaenoic acid (DHA)-containing oils (DHA at 10.7 mol% of the total fatty acids), in the form of phospholipids (PL), triacylglycerols (TG), and ethyl esters (EE) with the same constituent fatty acids, was investigated in the dark at 25°C in a bulk phase, and compared with that of control palm oil (supplemented with 20% soybean oil). The oxygen absorption of the DHA-containing oil was significantly lower in the form of PL than in the form of TG and EE during a 10-week oxidation, and the oxygen absorption of PL was almost equivalent to that of the control oil. A gas chromatographic analysis showed that 90% of initial DHA was retained in the form of PL after the 10-week oxidation, while TG and EE respectively more rapidly decayed with the loss of 97% and 64% of DHA. Tocopherol in the form of TG and EE had also completely decayed after the oxidation, while 37% of the initial tocopherol remained in the form of PL. The peroxide and carbonyl values of TG and EE showed large increases after the oxidation, but no such increase was observed for PL. These results show that DHA-containing oil in the form of PL was more resistant to the oxidative degradation of DHA than that in the form of TG and EE in a bulk phase.