Preparation and Properties of Sodium Alginate-Immobilized Rhizopus delemar Lipase

The immobilization of Rhizopus delemar lipase in sodium alginate gel spheres was studied.Enzyme powder and sodium alginate were dissolved in an HAc-NaAc buffer at pH 5.0,and then the mixture was added dropwise into a 0.05 mol/L CaCl_2 solution.After solidification in the solution for 45 min followed by filtration,rinsing and drying,immobilized enzyme beads were gained with a 34.1% activity recovery of the total enzyme added.The thermal stability of the immobilized enzyme was tested.There was only 36.2% loss of enzyme activity when the immobilized lipase was heated at 100 ℃ for 1 h,while the free enzyme lost all its activity when heated at 60 ℃ for 1 h.After incubation at 100 ℃ for 6 h,the immobilized enzyme still kept 46.8% of the(original) activity.The optimal reaction temperature of the immobilized enzyme for the olive oil hydrolysis was(90 ℃) compared to 40 ℃ of the free lipase.The Michaelis constant of the immobilized lipase was 8.1 mg/ml,and that of the free lipase was 13.8 mg/ml.The immobilized lipase was employed to catalyze the esterification in a non-aqueous solution,and it maintained 95% of the activity after consecutive use 6 times.