A novel and efficient method for the immobilization of thermolysin using sodium chloride salting-in and consecutive microwave irradiation

► Salting-in and microwave irradiation were combined to immobilize thermolysin. ► The maximum immobilized enzyme activity was 4.5-fold of that using normal method. ► Both the thermal stability and stability against organic solvents were enhanced. Sodium chloride salting-in and microwave irradiation were combined to drive thermolysin molecules into mesoporous support to obtain efficiently immobilized enzyme. When the concentration of sodium chloride was 3M and microwave power was 40W, 93.2% of the enzyme was coupled to the support by 3min, and the maximum specific activity of the immobilized enzyme was 17,925.1Umg−1. This was a 4.5-fold increase in activity versus enzyme immobilized using conventional techniques, and a 1.6-fold increase versus free enzyme. Additionally, the thermal stability of the immobilized thermolysin was significantly improved. When incubated at 70°C, there was no reduction in activity by 3.5h, whereas free thermolysin lost most of its activity by 3h. Immobilization also protected the thermolysin against organic solvent denaturation. The microwave-assisted immobilization technique, combined with sodium chloride salting-in, could be applied to other sparsely soluble enzymes immobilization because of its simplicity and high efficiency.