Synthesis of structured lipid 1,3-dioleoyl-2-palmitoylglycerol in both solvent and solvent-free system

• Facile methods for synthesis of high purity OPO have been established.
• Lipozyme TL IM and Lipozyme RM IM have different performances in solvent and solvent-free system.
• In acidolysis reaction, Lipozyme RM IM could be reused at least 15 times.
• In acidolysis reaction, Lipozyme TL IM was almost disposable.

To obtain high purity of 1,3-Dioleoyl-2-palmitoylglycerol (OPO), an important structured triglyceride for infant formula, a facile method was established. Tripalmitin (PPP) was firstly synthesized, and then OA was incorporated into the sn-1 and 3 position of the PPP glycerol backbone by acidolysis catalyzed using sn-1,3 regiospecific lipases. Two kinds of widely used immobilized sn-1,3 regiospecific lipases, Lipozyme TL IM and Lipozyme RM IM, were investigated in both solvent (n-hexane) and solvent-free system. The results showed that Lipozyme TL IM and Lipozyme RM IM were suitable for solvent system and solvent-free system respectively. Other reaction conditions (enzyme load, substrate molar ratio, temperature, reaction time) were optimized. The palmitic acid (PA) at the sn-2 position of the obtained triacylglycerols (TAGs) under optimized conditions were 92.92% and 86.62%, and OPO contents in the final products were 32.34% and 40.23% in the solvent and solvent-free system respectively. Special emphasis was given to test the reusability of the two immobilized lipases, results showed that Lipozyme TL IM was almost non-reusable, while Lipozyme RM IM could keep its activity for at least 15 times (about 60 h). These results provide a guide for the industrial production of high purity OPO by facile method.