Influence of the Drying Technique of Silica Gels on the Enzymatic Activity of Encapsulated Lipase

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Abstract
Recent studies by Reetz et al. (Reetz, M.T., Zonta, A. and Simpelkamp, J. (1996a) Biotechnology and Bioengineering, 49, 527-534) have shown that the catalytic activity of lipase encapsulated in sol-gel materials, in esterification reactions, depends on many parameters such as the presence of hydrophobic groups grafted on the gel network and of an organic component in the gel network. In the present study, we have examined the effect of the gel pore texture which can be modified by varying the drying technique, for a given silica precursor composition and hydrolysis-condensation procedure. For a given mixture of two silane precursors, propyltri-methoxysilane and tetramethoxysilane, we compared the effects of the presence or absence of an organic component such as polyvinyl alcohol, in combination with drying either by evaporation which leads to the formation of xerogels, or by supercritical drying in CO2 which leads to the formation of aerogels. For this last technique, the exchange of liquid is also an important step and its effect on the enzyme activity has been examined. The gel pore texture was characterized by nitrogen absorption according to the Brunauer Emmett and Teller method. The catalytic activities of the materials were compared in the esterification of lauric acid by 1-octanol.