The inhibitory effect of xylan on enzymatic hydrolysis of cellulose is dependent on cellulose ultrastructure

The inhibitory effect of xylan on enzymatic hydrolysis of cellulose with different ultrastructure is not clear. In this work, cellulose II, cellulose III, and amorphous cellulose were prepared from cellulose I by NaOH, ethylenediamine, and ball-milling treatment, respectively. Their crystalline structure and enzymatic hydrolyzability were systematically characterized and compared with cellulose I. Furthermore, the inhibitory effect of xylan on cellulose with different ultrastructure was investigated in detail. Results suggested that the enzymatic hydrolyzability of different cellulose increased in sequence from cellulose I (25.4%), cellulose III (41.7%), cellulose II (56.2%) to amorphous cellulose (77.4%) at enzyme loadings of 5.56 mg protein/g substrate. The enzymatic hydrolyzability of allomorphic cellulose was strongly inhibited by xylan, while a little inhibition was observed for amorphous cellulose. It was found that cellobiose released from different cellulose was decreased after the addition of xylan. At the initial hydrolysis stage, the inhibition degree was obviously increased for all of different cellulose, and then, the inhibition degree of cellulose I and cellulose II gradually decreased as enzymatic hydrolysis proceeded, while the inhibition degree of cellulose III and amorphous cellulose had changed a little. In addition, at a longer time of hydrolysis, the inhibition degree was decreased with the increase of cellulase dosage except for cellulose III, which remained approximately unchanged. Overall, this study demonstrated that the inhibitory effect of xylan on cellulose hydrolysis was substantially affected by the ultrastructure of cellulose, and thus it provides new insights for relieving the inhibitory effect of xylan by altering the ultrastructure of cellulose.