Influence of the drying technique of silica gels on the enzymatic activityof encapsulated lipase

Recent studies by Reetz ct al. (Reetz, M.T., Zonta, A. and Simpelkamp, J. ( 1996a) Biotechnology and Bioengineering, 49, 527-534) have shown that the c atalytic activity of lipase encapsulated in sol-gel materials, in esterific ation reactions, depends on many parameters such as the presence of hydroph obic groups grafted on the gel network and of an organic component in the g el network. in the present study, we have examined the effect of the gel po re texture which can be modified by varying the drying technique, for a giv en silica precursor composition and hydrolysis-condensation procedure, For a given mixture of two silane precursors, propyltrimethoxysilane and tetram ethoxysilane, we compared the effects of the presence or absence of an orga nic component such as polyvinyl alcohol, in combination with drying either by evaporation which leads to the formation of xerogels, or by supercritica l drying in CO2 which leads to the formation of aerogels. For this last tec hnique, the exchange of liquid is also an important step and its effect on the enzyme activity has been examined. The gel pore texture was characteriz ed by nitrogen absorption according to the Brunauer Emmett and Teller metho d. The catalytic activities of the materials were compared in the esterific ation of lauric acid by l-octanol.