Crystallinity and Enzymatic Hydrolysis of Cryomilled Rice Hull Cellulose

Abstract

Rice hulls have good potential as a new carbohydrate resource. However, the polysaccharides contained in rice hull are desired to be hydrolyzed to sugars and appropriate pretreatments are essential in order to enhance their susceptibility to the enzyme, because cellulose, xylan, lignin and silicate are firmly bound in the rice hull as structural supports. The effects of cryomilling of rice hull was the reduction of its bulk so that the volume was reduced to about one fourth of its original volume and no crystalline form of the treated cellulose was observed from X-ray diffractogram. The cryomilling of rice hull cellulose increased enzymatic hydrolysis rates and yields of glucose over 10 times but not completely. This means that it is not able to disrupt completely the physical structure of the components such as lignin, which causes steric hindrance of enzyme action to cellulose, surrounding the cellulose fiber by physical treatment. However, the cryomilled cellulose extracted by cellulose solvent or treated with lignin solvent was almost completely saccharified by only Cx-glucanase of Asperigillus niger without using C1-enzyme of Trichoderma viride. On the other hand, hemicellulose and silicate did not disturb enzyme reaction to cellulose.