In literature, only few papers are available on the cellulases immobilization. This is due to the fact that cellulose is not soluble and some immobilization techniques, such as enzymes entrapment, impede the interaction enzyme-substrate. Immobilization of cellulases via covalent bonds appears to be the most suitable technique. Besides the enzyme stabilization, the covalent-immobilization allows the use of supported enzymes for several cycles of reactions (Brady & Joordan, 2009; Li et al., 2007; Mateo et al., 2007; Dourado et al., 2002; Yuan et al., 1999).

In 1999, Yuan and coworkers, immobilized cellulases onto acrylamide grafted acrylonitrile copolymer membranes (PAN) by means of glutaraldehyde. They showed that the enzyme stability was increased after the immobilization process. Also, the activity of the immobilized cellulases was higher than the free cellulases at pH 3 — 5 and at temperatures above 45 °C (Yuan et al., 1999).

In 2002, cellulases from T. reesei were immobilized on Eudragit L-100 by researchers of the University of Minho (Portugal). They used the commercial mixture Celluclast® 1.5L supplied by Novozymes (Denmark). This method allowed to improve the stability of the enzymes without significant loss of its specific activity. The adsorption of cellulases on Eudragit lowered the enthalpy of denaturation, but affected only slightly the denaturation temperature (Dourado et al., 2002).

In 2006, Li and coworkers, immobilized cellulase enzymes by means of liposomes. These are phospholipid vesicle, ranging in size from 25 nm to 1pm. In this method, glutaraldehyde — activated liposome bound to the enzyme thus forming the liposome-cellulase complex. Following this step, the complex was immobilized on chitosan-gel. The immobilized enzyme by the liposome molecules showed efficiency higher by 10% compared to the enzyme immobilized in chitosan-gel without liposome. The immobilized cellulase-liposome complex showed a loss of activity of 20% with respect to the original value after six cycles of reaction. Therefore, liposome-binding cellulase appeared to prevent or limit the enzyme deactivation (Li et al., 2007).

In recent investigations, two commercial cellulase enzymes (Celluclast 1.5 and Novozym 188) were immobilized on epoxy Sepabeads® support (Resindion s. rl.). The preliminary data showed that 60% of loaded Celluclast proteins were adsorbed by the support and that more than 90% of these proteins remained stably linked even after repeated washings (Verardi et al., 2011).