Preparation of Chiral Triacylglycerols, sn-POO and sn-OOP, via Lipase-mediated Acidolysis Reaction

It is well known that lipases are useful tools for preparing various structured triacylglycerols (TAGs). However, the lipase-mediated preparation of chiral TAGs has never been reported. This study aimed to prepare chiral TAGs (viz., 1-palmitoyl-2,3-dioleoyl-sn-glycerol (sn-POO) or 1,2-dioleoyl-3-palmitoyl-sn-glycerol (sn-OOP)) via lipase mediated acidolysis, using triolein (TO) and palmitic acid (P) as substrates. Three commercially available lipases (viz., Lipozyme RM-IM®, Lipozyme TL-IM®, and Lipase OF®) were used. Lipozyme RM-IM® resulted in an increase 1P-2O (sn-POO + sn-OOP + 1,3-dioleoyl-2-palmitoyl-sn-glycerol) content with reaction time, which plateaued at 2~24 h (max. yield 47.1% at 4 h). The highest sn-POO/sn-OOP ratio of ca. 9 was obtained at 0.25 h, and the rate got close to 1 with reaction time (sn-POO/sn-OOP = 1.3 at 24 h). Lipozyme TL-IM® resulted in a lower 1P-2O synthesis rate than Lipozyme RM-IM®, where its highest sn-POO/sn-OOP ratio of ca. 2 was obtained at 0.25 h and did not vary much further with reaction time. In the case of Lipase OF®, its reaction rate for 1P-2O synthesis was lower than that of the other two lipases, and the highest sn-POO/sn-OOP ratio of ca. 1.4 was obtained at 0.5 h, reaching closer to 1 with a longer reaction time. Reaction solvents (viz., hexane, acetone, and benzene) also affected the 1P-2O preparation, where the highest 1P-2O content was obtained with the solvent-free system. Furthermore, the solvent-free system showed a higher reaction rate for 1P-2O synthesis than did the hexane system, with no effect on chiral specificity of the lipase for the TAG molecules. These results suggested that among three types of commercial lipase, Lipozyme RM-IM® is the most useful for the preparation of chiral TAGs by acidolysis reaction.