Evaluation of the effect of hot-compressed water treatment on enzymatic hydrolysis of lignocellulosic nanofibrils with different lignin content using a quartz crystal microbalance.

Hot-compressed water (HCW) treatment is known to not only improve enzymatic hydrolysis efficiency of lignocellulosic biomass but to also generate insoluble lignin droplets, which retard enzymatic hydrolysis. In this study, the inhibitory effect of the lignin droplets was evaluated by monitoring the initial enzyme adsorption and degradation of lignocellulosic nanofibrils (LCNFs) using a quartz crystal microbalance (QCM). Lignin content was adjusted by the sodium chlorite-acetic acid method and divided into samples with high (24.9 wt%) and low (5.6 wt%) lignin content, which were then subjected to HCW treatment at various temperatures. The changes in lignin content were small with increasing HCW temperature, whereas hemicellulose content decreased, regardless of the initial lignin content. The formation of lignin droplets and pseudo-lignin-like products was confirmed in both LCNFs by atomic force microscopy (AFM) and was predominant in LCNFs with high lignin content treated at 200°C. QCM data showed that the enzyme adsorption amount in both LCNFs after HCW treatment was increased and was greater in LCNFs with low lignin content. Initial enzymatic degradation was substantially slowed in LCNFs with high lignin content, particularly after HCW treatment at temperatures higher than 180°C. These QCM results suggest that the steric hindrance of the deposited lignin is the primary mechanism by which the initial enzymatic hydrolysis is delayed. Biotechnol. Bioeng. 2016;113: 1441-1447.