Microwave-assisted biosynthesis of glycerol monolaurate in reverse microemulsion system: key parameters and mechanism

This study highlights the microwave-assisted biosynthesis of glycerol monolaurate catalyzed by Novozym 435 in reverse microemulsion system dispersed by Aerosol-OT. Optimization of key parameters including catalyst/surfactant loading and temperature showed that under microwave irradiation, 125.9 mol L⁻¹ (36 wt%) of glycerol monolaurate was achieved within 30 min, which had improved 150% compared with that of water bath under the same conditions (60 °C, 1 wt% enzyme, 5 wt% AOT). Also, a synergistic effect of microwave irradiation and Aerosol-OT on reaction and a decline of optimum temperature (from 70 to 60 °C) were observed in comparison with traditional heating. More importantly, further comparative studies on morphology and chemicophysical profiles of reaction system heated by different thermal modes revealed the following: (1) due to the volumetric and selective heating character of molecular heating, superiorly larger interface of reaction system was formed under microwave irradiation, directly accelerating the reaction course investigated; and (2) microwave irradiation more favored a less compact state of enzyme. And faster mobilities of lid structure of enzyme were evident under microwave irradiation. This enhancement might facilitate the transition of conformational states, which is of key importance for the activation of bioactivity of Novozym 435. Moreover, the stepwise changes in steady-state fluorescent profiles demonstrated that the thermal-induced variation was not two-state transition but involves intermediate states, which was further supported by activity measurements reflected in glycerol monolaurate yield.