Kinetic studies on enzymatic hydrolysis of celluloses for evaluation of amorphous structures

Abstract

Enzymatic hydrolysis of never-dried, freeze-dried, and oven-dried amorphous celluloses, and crystalline cellulose was studied for evaluation of amorphous structures of cellulosic materials. Hydrolysis rate constants at the initial stage were indirectly measured using a glucose sensor, and Km and V max values were obtained from the v o /[ S] o versus [ S] o plots. The decreasing order of 1/ Km values was as follows: never-dried amorphous cellulose ⪢ solvent-exchanged amorphous cellulose ≥ freeze-dried amorphous cellulose > oven-dried amorphous cellulose ≥ microcrystalline cellulose powder. On the other hand, the decreasing order of V max was as follows: never-dried amorphous cellulose ≥ solvent-exchanged amorphous cellulose > freeze-dried amorphous cellulose = microcrystalline cellulose powder > oven-dried amorphous cellulose. These observations indicated that 1/ Km and V max values reflected subtle differences in amorphous structure. Almost no relationship was observed between those values and either crystallinity or specific surface area determined by the nitrogen adsorption method. Thus, kinetic studies of enzymatic hydrolysis of cellulose samples may be applicable for the characterization of non-crystalline regions of cellulose.