Immobilized enzymes offer many advantages over the free counterparts. These advantages include, but not limited to, easy separation, reuse ability, induced stabilities and the potential of continuous operation. However, the immobilization process at the same time causes some drawbacks including lost of catalytic activity of the immobilized enzymes. Many interpretations have been given to explain the reasons behind such drawback. Some of them related to the enzymes themselves, such as deactivation of enzymes and miss-orientation. Others refer to the diffusion limitation of substrates and/or to inhibitory effects of the products. Substrate diffusion limitation presents the serious one.
In this review, mainly, strategies for overcoming this drawback namely; Immobilization of the enzymes on soluble-insoluble matrices, Immobilization of the enzymes on thermally reversible hydrogels, Immobilization of the enzymes on pressure-sensitive gels, Processing the enzymic reaction under non-isothermal conditions, and finally, Immobilization of enzyme on carriers' surface are presented and discussed.