The aim of this study was to evaluate the combination of supercritical carbon dioxide (SCCO2) and membrane separation technologies in the purification of structured lipids (SLs) previously obtained. The SLs (modified triacylglycerols) were obtained from enzymatic interesterification between medium-chain triacylglycerols (MCT) and ethyl esters of long-chain fatty acids (EtELCFA). This process generates by-products that must be removed from the reaction medium to obtain pure SLs. The purification process was carried out by extraction of the by-products from the reaction medium with supercritical CO2 and further selective retention of SLs using membranes integrated within the extractor. Two nanofiltration membranes (Osmonics DL4040-C and HL4040-F) and one reverse osmosis membrane (DOW Chemical BW30-4040) were evaluated. Pressures of 9, 11 and 13 MPa were used in the retentate side, and transmembrane pressures (TMP) in the range 0.7-4 MPa were applied. All experiments were conducted at 40 degrees C. The effect of these pressures on selectivity during the reaction's by-product extraction and retention of SLs by the membrane were analyzed. Results showed that pressures on the retentate side and the TMP are very important parameters in the solubilization and permeation of triacylglycerols, fatty acids and ethyl esters of fatty acids. Retention of 100% of SLs and maximum permeation of reaction by-products were reached at pressure of 9 MPa and TMP of 0.7 MPa, using the BW30-4040 reverse osmosis membrane. (c) 2007 Elsevier B.V. All rights reserved.