Polyvinyl formal (PVF) resin plate was used as a support for forming organic-inorganic hybrid sol-gel polymer within its pores. Candida cylindracea lipase immobilized by entrapment in such hybrid sol-gel polymers made from tetramethoxysilane (TMOS) and propyltrimethoxysilane (PTMS) could efficiently catalyze direct esterification reaction between geraniol and acetic acid in anhydrous hexane for synthesis of the flavor ester geranyl acetate. The Optimum formulation of the sol-gel solution for enzyme activity should be made with PVF plate with 250 mum mean pore diameter, PTMS molar percentage = 80%, enzyme loading at 60 mg lipase/g gel, water to silane molar ratio = 25, and 4 ml PVA solution (4% w/w). The specific activity of the immobilized enzyme is 7.4 times that of the free enzyme with a protein immobilizing efficiency of 93%. The substrate inhibition by acetic acid was alleviated with the optimum acetic acid concentration, which gives the highest enzyme activity, increasing from 15 to 35 mM after enzyme immobilization. Excellent thermal stability was found for the immobilized enzyme, where full retention of enzyme activity was found after incubated at 90degreesC for 2 h. When stored at room temperature, the immobilized enzyme did not show any activity loss for up to I month. The operational stability also increased 51-fold after entrapment in sol-gel polymer. (C) 2003 Elsevier Inc. All rights reserved.
