A specified amount of lipase PS (optimally 1 g) was
measured into a flask and 10ml of water was added.
The mixture was stirred at 150 rpm using a magnetic stir-
rer for about 5min. To this mixture, 1ml of a 1M NaF
solution and the silica precursors were added. Upon the
addition of the precursors, the reaction occurred almost
immediately and the gel was formed in 2min. The flask
was removed from the stirrer and left sealed at room
temperature for 24 h. The flask was then uncapped and
was incubated in a water bath at 33C for about 24 h.
The ceramic polymer was then broken up and grounded
in a mortar. The powder was washed with 100ml of dis-
tilled water in a 250ml flask for 1 h at a mixing speed of
500 rpm. The mixture was then filtered. About 90ml of
supernatant was collected. This supernatant was further
examined for its residual activity (see the section on the
Degree of immobilization tests). The wet paste was dried
again at 33C for 24 h. The immobilized lipase was then
crushed in a mortar to yield the final product. The fine
powder was stored at 4C until use. About 6 g of the
sol–gel material was resulted in this procedure. Based
on the degree of immobilization tests, about 95% of
the enzyme was immobilized in this procedure. The ac-
tual enzyme loading was determined at 475mg of lipase
PS per 3 g of gel.