Enzymatic hydrolysis of cellulose : physico-chemi-cal properties of cellulose and their effects on hydrolysis kinetics and mechanisms

Abstract

As a part of our research endeavor to develop alternate energy and chemical resources from biomass, fundamental studies on the structural properties of cellulose and their effects on cellulase hydrolysis kinetics have been undertaken. The structural properties of cellulose are significantly changed not only during the reaction but also when the cellulosic materials are subjected to physicochemical pretreatment. The effects of pretreatment on the susceptibility of cellulose, the changes in such properties of cellulose as crystallinity, degree of polymerization, accessibility of water to cellulose surface, and surface area and the effect of these changes due to pretreatment on the kinetics of enzymatic hydrolysis have been studied. Among those physical studied, the crystallinity of cellulose was found to be most significant effect on the hydrolysis kinetics. Based on the experimental results, a two-phase kinetic model which takes into consideration of simultaneous enzymatic hydrolysis of both the crystalline and amorphous cellulose was developed. In order to further our understanding of the effect of cellulose structure on the enzymatic hydrolysis, the changes in structural parameters of cellulose during the course of hydrolysis have been studied. Some attempts were made to elucidate the relationships between the changes in the hydrolysis rate and adsorption pattern of enzyme and the changes in structural parameters of cellulosic substrates as the reaction proceeds. It was found that the hydrolysis rate or breaking of $\beta$-1,4-glycosidic bond in the cellulose is mainly governed by the crystallinity and that the two-phase hydrolysis concept was valid. The surface area appears to have some effect on the adsorption of cellulase, although the extent of this effect is not so significant as the crystallinity when the reaction proceeds. The changes in the degree of polymerization are dependent on the pore size of cellulose or the accessibility of enzyme molecule to t...