Effect of ionic liquids on enzymatic preparation of lipophilic feruloylated structured lipids using distearin as feruloylated acceptor and kinetic analysis

Feruloylated acylglycerols (FAGs) are lipophilic structured lipids of ferulic acid (FA), which have antioxidant activities and UV-absorbing properties. In the paper, FAGs were prepared by the enzymatic transesterification of ethyl ferulate (EF) with distearin using ionic liquids (ILs) as the reaction media. The effects of ILs on the enzymatic transesterification and the selective formation of lipophilic FAGs or hydrophilic glyceryl ferulates (FGs) were investigated. The effect of reaction variables on the transesterification was optimized using response surface method (RSM), and kinetic analysis in the IL was also evaluated. Among the tested ILs, excellent FAGs selectivity (~0.63) was achieved using [Emim]TF2N as the reaction solvent. Moreover, [Emim]TF2N also showed protective effect on the enzyme stability at high temperature (110 °C). High EF conversion (99.7 ± 0.3%) and FAGs yield (68.7 ± 1.0%) were also obtained at the optimized conditions (reaction temperature of 95 °C, reaction time of 28 h, and enzyme load of 15% (w/w, relative to the weight of substrates)). The activation energies (Ea) of EF conversion, FGs and FAGs formation were 44.4, 41.4, 59.9 kJ/mol, respectively. KmA, KmB and Vmax were 0.02, 0.12 mol/L, and 4.54 mmol/(L·h), respectively. The kinetics of transesterification of EF with distearin in [Emim]TF2N agreed with the Ping-Pong Bi-Bi mechanism without substrates inhibition.