Synthesis of geranyl acetate by esterification with lipase entrapped in hybrid sol-gel formed within nonwoven fabric

Candida cylindracea lipase was entrapped in organic-inorganic hybrid sol-gel polymers made from tetramethoxysilane (TMOS) and alkyltrimethoxysilanes. By forming the gels within the pores of a nonwoven polyester fabric, a novel immobilized biocatalyst in sheet configuration based on sol-gel entrapment of the enzyme was obtained. Lipases immobilized in sol-gel matrices efficiently catalyzed the direct esterification reaction of geraniol and acetic acid in anhydrous hexane to produce geranyl acetate. The optimal formulation of the sol-gel solution for enzyme immobilization was at a 20:1 molar ratio of water to total silane; a 4:1 molar ratio of propyltrimethoxysilane to TMOS; hydrolysis time at 30 min; and enzyme loading of 200 mg lipase/g gel. Under these conditions, protein immobilization efficiency was 91%, and the specific activity of the immobilized enzyme was 2.6 times that of the free enzyme. Excellent thermal stability was found for the immobilized enzyme in dry form or in hexane solution in the presence of acetic acid, in which case severe inactivation of free enzyme was observed. The immobilized enzyme retained its activity after heating at 70°C for 2 h, whereas the free enzyme lost 80% of its activity.