Enzymatic synthesis of 1,3-oleic-2-medium chain triacylglycerols and strategy of controlling acyl migration: insights from experiment and molecular dynamics simulation

Abstract

ABSTRACT Medium- and long-chain triacylglycerols (MLCTs) with high 1,3-oleic-2-medium chain (OMO) triacylglycerols content were synthesized by the acidolysis reaction between Cinnamomum camphora seed oil (CCSO) and oleic acid, catalyzed by lipozyme RM IM. In addition, the simultaneous rate of acyl migration (RAM) was investigated during the esterification process. The maximal yield of OMO-structured triacylglycerols (YST) was up to 64.45% under the optimum condition: the molar ratio of CCSO to oleic acid, 1:4; enzyme dosage, 10 wt%; temperature, 60°C; and reaction time, 24 h. RAM was 28.66% at same time. It is shown that YST positively related to RAM at single experiments of the molar ratio (r2 = 0.999, P< .01), enzyme dosage (r2 = 0.988, P< .01), below 60°C of temperature (r2 = 0.923, P< .05) and within 24 h of reaction time (r2 = 0.940, P< .05). However, YST was negatively correlated with RAM at a temperature higher than 60°C (r2 = −0.682, P> .05) or a reaction time longer than 24 h (r2 = −0.594, P> .05). The effect of temperature on the reaction could be verified by molecular dynamics simulation, opened enzyme lids were increased with temperature elevated, and helped substrates invade into catalytic triad. When temperature rose to higher than 333 K (60°C), rearrangement of the catalytic triad was promoted, which resulted in both decreasing enzyme catalytic activity and irritating acyl migration. This study could help understand the trigger cause of acyl migration at high temperature, and conclusively reaction temperature was a vital factor to balance YST and RAM in a solvent-free system. OMO-structured triacylglycerols might possess a potential application as a new type of nutritional lipids for daily diet.