Entrapment or encapsulation is to entrap the enzyme in a polymer
network (gel lattice), such as an organic polymer, a silica
sol-gel, or a membrane device such as a hollow fiber or a microcapsule.
Additional covalent attachment is required. Entrapment
requires the synthesis of a polymeric network in the presence of
the enzyme. Typically, alginic acid-based microencapsulation
forms an insoluble polymeric matrix for enzyme entrapment.
In fact, alginate microbeads or microspheres have been used in
the enzymatic reactor process. But, due to their mechanical stability,
their utilization is limited to only a few applications [23].
In addition, a novel polymer-incarceration methodology for immobilizing
enzymes has been reported recently. Polystyrenewith
pendant hydrophilic tetraethylene glycol and glycidol moieties
and dichloromethane can cause coacervation with an enzyme
after adding 1-hexane, leading to a precipitate containing the
enzyme in the polymer phase. In water, organic chemicals are
not uniformly dispersed but may be separated out into layers or
droplets. If the droplets formed contain a colloid, rich in organic
compounds and surrounded by a tight skin of water molecules,
then they are known as coacervates [24]. Of course, entrapment
of enzyme in polymer network can protect enzymes by preventing
direct contact with the environment, thereby minimizing the
effects of gas bubbles, mechanical sheer, and hydrophobic solvents,
but has the drawback ofmass transfer limitations and low
enzyme loading.