Walnut Oil - Unexplored Raw Material for Lipase-Catalyzed Synthesis of Low-Calorie Structured Lipids for Clinical Nutrition

Abstract

Low-calorie structured lipids that contain medium-chain fatty acids in the sn-1 and sn-3 positions of the glycerol backbone, and long-chain fatty acid in the sn-2 (MLM type) were synthesized in one-step acidolysis of walnut oil with caprylic acid. Caprylic acid residues were incorporated selectively into sn-1,3 positions of triacylglycerols using 1,3-specific immobilized lipases from Rhizomucor miehei (Lipozyme) and Rhizopus delemar (PP-RhDL) as catalysts. Under the optimal reaction conditions, we achieved an excellent yield of the desired MLM-type structured lipids (97 mole % with Lipozyme and 96.4 mole % with PP-RhDL). The synthetic activity of PP-RhDL was not influenced by the reaction medium whereas the Lipozyme was more effective in hexane than in solvent-free medium. The same degree of conversion of initial triacylglycerols was observed for the two enzymes in four consecutive reaction cycles. The amount of MLM-type structured lipids, however, decreased with each following cycle at the expense of mono-substituted with caprylic acid triacylglycerols (MLL type). Practical Applications Structured lipids (SLs) that contain medium-chain fatty acids in the sn-1 and sn-3 positions of the glycerol backbone, and long-chain fatty acids in the sn-2 (MLM type) are known to improve liver function, minimize risk of infections, and reduce the number of gastrointestinal complications in patients undergoing major abdominal surgery and are used in clinical nutrition as well as specialized food for athletes because they provide fast energy supply. After an enzymatic modification of walnut oil, high yield of SLs with caprylic acid residue in the sn-1 and sn-3 positions of the glycerol backbone and long-chain fatty acid residue in the sn-2 position of triglycerides was obtained.