Purification of 1,2-diacylglycerols from vegetable oils: Comparison of molecular distillation and liquid CO2 extraction

High oleic sunflower oil (HOSO) and soybean oil (SBO) were partially deacylated by enzyme-catalyzed propanolysis using lipozyme TL IM to form 1,2-diacyl-sn-glycerols (1,2-DAG) in 40% yields. 1,2-DAG are of interest as potential regiospecific intermediates in the synthesis of structured lipids for cosmeceutical and nutriceutical applications. Two purification techniques were examined to determine which was the most efficient at removing the fatty acid propyl ester (FAPE) byproducts while limiting the spontaneous acyl migration of the 1,2-DAG to 1,3-diacyl-sn-glycerols (1,3-MAG) and adversely affecting the physical properties of the 1,2-DAG and FAPE. Molecular distillation of the partially deacylated vegetable oils was examined at temperatures ranging from 120 to 240 °C. Molecular distillation at 220 °C removed 77% of the FAPE byproduct but caused significant acyl migration. Additionally, the acid values and Lovibond color of the partially deacylated vegetable oils were deleteriously affected. The purity of the FAPE, contaminated by co-distillation of di- and mono-acylglycerol species as monitored by viscosity values and 1H NMR, was also compromised by the high temperature distillation. Distillations at lower temperatures improved the physical properties of the partially deacylated vegetable oils and the purity of the FAPE but at the sacrifice of the efficiency of FAPE removal. The mild condition of the liquid CO2 extraction afforded the most efficient removal of the FAPE, 96%, while causing no appreciable acyl migration, and resulted in acid values and Lovibond colors comparable to those obtained at the lowest molecular distillation temperatures studied.