Bioactivity of Lipase Encapsulated in Aluminosilicate Gels

Pseudomonas cepacia lipases were encapsulated in a series of aluminosilicate gels made in different conditions in terms of pH, ratio r(w) of hydrolysis water per cation, ratio of r(Si/Al) of Si to Al cations, nature of the silica precursor and drying technique. The effect of these parameters on the catalytic activity of lipase in the esterification of 1-octanol by lauric acid were compared and related to different drying mechanisms around the enzymes inside the gel networks. In particular, the gel texture and structure were studied by nitrogen adsorption according to the Brunauer, Emmett and Teller (BET) method, Fourier Transform Infrared spectroscopy (FTIR), Infrared absorbance after absorption of pyridine and Al-27 Nuclear Magnetic Resonance (NMR). This study showed that the gel structure could accelerate the enzyme activity by providing local water sinks, dispersed in the gel, to capture the water produced during esterification. The net effect is that the esterification reaction is displaced in a favorable direction. Aluminosilicate gels with such sinks due to the Al atoms could be used as good encapsulating media, without needing hydrophobic functions on the silica network.