Enzyme-catalyzed synthesis and oxidative stability of DHA-rich re-esterified triacylglycerol from microalgae oil

DHA content of crude microalgae oil was about 36-44%, and the next abundant fatty acid was palmitic acid (36-42%). In this study, enzyme-catalyzed glycerolysis reaction was performed with microalgae free fatty acid (FFA) substrates enriched with DHA for the synthesis of DHA-rich re-esterified triacylglycerol (rTG). The DHA-rich microalgae FFA substrates were prepared from microalgae oil triacylglycerols (TAG) by urea fractionation and saponification-acid hydrolysis. The DHA content of the prepared DHA-rich microalgae FFA substrates increased from 44% to 74%, while the palmitic acid content decreased from 42% to 8%. The rTG containing 74% DHA was produced with a conversion rate of approximately 85% by enzyme catalyst. After purification via short path distillation, the effects of six antioxidants (ascorbyl palmitate, rosemary oil, tocopherol mixture and their combination) on the oxidative stability of the DHA-rich rTG were investigated in a dark oven at 60°C for 20 days. The oxidative stabilities of DHA-rich rTG were determined by peroxide value, p-anisidine value, unsaturation degree of fatty acid, and conjugated diene and aldehydes analyzed by ¹H-NMR. Overall, results indicated that the addition of a combination of ascorbyl palmitate 200 ppm + rosemary oil 500 ppm + tocopherol mixture 500 ppm can enhance the oxidative stability for the DHA-rich rTG oil. This research would provide optimized conditions for the enzymatic synthesis and oxidative stability of DHA-rich rTG oil.