Two-step synthesis of MLM-Type structured lipids using enzymatic or combined enzymatic and chemical reactions

Abstract

Structured lipids (SL) containing a mixture of medium-chain fatty acids (MCFA) and long-chain fatty acids (LCFA) in the same molecule have been designed for medical purposes. The placement of a long (L) chain fatty acid at the sn-2 position of glyceryl carbons, particularly if it is saturated, increases the digestibility of the lipid of the MLM kind, being in the sn-1 and sn-3 positions a medium (M) chain fatty acid. These SLs are reported to be helpful to the immune system and to improve lipid clearance, having application in the prevention of obesity and its associated medical conditions. The most studied process for the obtention of MLM is acidolysis between long-chain triacylglycerols (TAG) and MCFA in a one-step reaction. The most selective catalysts are some 1,3-specific lipases. However, this method requires an important post-reaction purification because the desired MLM triglyceride is obtained with other secondary and undesired products, such as mono and diglycerides, fatty acids and other triglycerides. Hydrolysis is a secondary reaction very difficult to avoid using commercial lipases. In addition, acyl migration is also present, with the generation of minor amounts of glycerol and MMM triglyceride. Several authors have reported a two-step process. In the first step, 2-monoacylglycerols (2-MAG) are obtained (from vegetable oils or TAGs with the desired fatty acids) by enzymatic alcoholysis using 1,3-specific lipases. In the second step, MCFAs are added in the extreme positions of 2-MAG by enzymatic esterification with 1, 3-specific lipases. This step can also be carried out with a novel heterogeneous catalyst. In this work, we review the status of the art on the two-step process of obtention of MLM triglycerides.