Sucrose hydrolysis by thermostable immobilized inulinases from Aspergillusficuum

The possibility of using thermostable inulinases from Aspergillus ficuum in place of invertase for sucrose hydrolysis was explored. The commercial inu linases preparation was immobilized onto porous glass beads by covalent cou pling using activation by a silane reagent and glutaraldehyde before adding the enzyme. The immobilization steps H ere optimized resulting in 3 suppor t with 5,410 IU/g of support (sucrose hydrolysis) that is 77% of the activi ty of the free enzyme. Enzymatic properties of the immobilized inulinases w ere similar to those of the free enzymes with optimum FH near pH 5.0, Howev er, temperature where the activity was maximal was shifted of 10 degreesC c lue to better thermal stability after immobilization with similar activatio n energies. The curve of the effect of sucrose concentration on activity wa s bi-phasic. The first part. for sucrose concentrations lower than 0.3 M fo llowed Michaelis-Menten kinetics with apparent E;,, and Vm only slightly af fected by immobilization. Substrate inhibition was observed at values from 0.3 to 2 M sucrose. Complete sucrose hydrolysis was obtained for batch reac tors with 0.3 and 1 M sucrose solutions. In continuous packed-bed reactor 1 00% (for 0.3 M sucrose), 90% (1 M sucrose) or 80% sucrose conversion were o bserved at space velocities of 0.06-0.25 h(-1). The operational half-life o f the immobilized inulinases at 50 degreesC with 2 M sucrose was 350 days. (C) 2001 Elsevier Science inc. All rights reserved.