Quartz crystal microbalance study on enzymatic degradation behavior of hemicellulose in the thin films of lignocellulosic nanofibrils

The effects of hemicellulose on the enzymatic degradation of lignocellulose were investigated using quartz crystal microbalance (QCM). It was found that the frequency changes in initial enzymatic degradation stage of lignocelluloses were different from the typical change for pure cellulose. In general, the frequency decreases due to the mass increase by the enzyme adsorption. In the case of lignocelluloses, however, the frequency was slightly increased in initial degradation stage and then decreased before increasing again. To study more deeply about this unique frequency changes, the effect of hemicellulose degradation was investigated. Thin films for QCM were prepared from two lignocellulosic nanofibers from hardwood and softwood (eucalyptus and hinoki), and pure hemicelluloses (xylan and mannan), and crude enzyme mixture and purified hemicellulases (xylanase and mannanase) were used as enzymes. The degradation of pure hemicelluloses by purified hemicellulases showed that the frequencies were rapidly increased without showing any decrease in the initial enzyme adsorption stage. The results suggest that hemicelluloses will also be degraded after hemicellulase adsorption, nevertheless the frequency increase due to of hemicellulose degradation is superior to the frequency decrease by hemicellulase adsorption. In addition, typical initial frequency decrease due to cellulase adsorption was detected after removing hemicelluloses in lignocellulosic nanofibers by hemicellulases. It can be suggested that the initial frequency increase detected during enzymatic degradation of lignocellulosic nanofibers by enzyme mixture is due to the hemicellulose degradation by hemicellulase in enzyme mixture. After removal of hemicelluloses, cellulase can adsorb on the increased cellulose surface, resulting in the frequency decrease.