Donglin Xin

α-l-Arabinofuranosidase (ARA), a debranching enzyme that can remove arabinose substituents from arabinoxylan and arabinoxylooligomers (AXOS), promotes the hydrolysis of the arabinoxylan fraction of biomass; however, the impact of ARA on the overall digestibility of cellulose is controversial. In this study, we investigated the effects of the addition of ARA on cellulase hydrolytic action. We found that approximately 15% of the xylan was converted into AXOS during the hydrolysis of aqueous ammonia-pretreated corn stover and that this AXOS fraction was approximately 12% substituted with arabinose. The addition of ARA removes a portion of the arabinose decoration, but the resulting less-substituted AXOS inhibited cellulase action much more effectively; showing an increase of 45.7%. Kinetic experiments revealed that AXOS with a lower degree of arabinose substitution showed stronger affinity for the active site of cellobiohydrolase, which could be the mechanism of increased inhibition. Our findings strongly suggest that the ratio of ARA and other xylanases should be carefully selected to avoid the strong inhibition caused by the less-substituted AXOS during the hydrolysis of arabinoxylan-containing biomass. This study advances our understanding of the inhibitory mechanism of xylooligomers and provides critical new insights into the relationship of ARA addition and cellulose digestibility.

During the conversion of lignocellulosic biomass to biochemical products, the end-products in the hydrolysate significantly inhibit cellulase efficiency and result in a low conversion yield. Our groups recently reported that cellobiohydrolase I (CBH I), the major enzyme in the cellulase mixture secreted by Trichoderma reesei, is susceptible to inhibition by xylan oligomers. In this work, effects of mannan with different structural properties, xylan and xylo-oligosaccharides (XOS) with different chain lengths on the hydrolytic action of CBHII, another key protein in commercial cellulase preparation, were investigated. Mannan and xylan oligomers blocked the adsorption of CBHII onto the cellulose surface and decreased the hydrolytic efficiency of CBHII. The ability of mannan in hindering the interaction of CBHII with cellulose varied with the physical properties of mannan. Mannan with high viscosity and galactose side units showed a stronger inhibitory effect on the efficiency of CBHII as compared with those with low viscosity and galactose side units. The inhibitory effect of XOS on the CBHII action decreased with the reduction of XOS chain length. Aside from CBHII, synergism between CBHI and CBHII was strongly inhibited by xylan and XOS. The results thus indicated the necessity of producing highly active CBHs that could minimize the product inhibition of cellulase in cellulose conversion to sugars.

During conversion of bamboo into biofuels and chemicals, it is necessary to efficiently predict the chemical composition and digestibility of biomass. However, traditional methods for determination of lignocellulosic biomass composition are expensive and time consuming. In this work, a novel and fast method for quantitative and qualitative analysis of chemical composition and enzymatic digestibilities of juvenile bamboo and mature bamboo fractions (bamboo green, bamboo timber, bamboo yellow, bamboo node, and bamboo branch) using visible–near infrared spectra was evaluated. The developed partial least squares models yielded coefficients of determination in calibration of 0.88, 0.94, and 0.96, for cellulose, xylan, and lignin of bamboo fractions in raw spectra, respectively. After visible–near infrared spectra being pretreated, the corresponding coefficients of determination in calibration yielded by the developed partial least squares models are 0.994, 0.990, and 0.996, respectively. The score plots of principal component analysis of mature bamboo, juvenile bamboo, and different fractions of mature bamboo were obviously distinguished in raw spectra. Based on partial least squares discriminant analysis, the classification accuracies of mature bamboo, juvenile bamboo, and different fractions of bamboo (bamboo green, bamboo timber, bamboo yellow, and bamboo branch) all reached 100 %. In addition, high accuracies of evaluation of the enzymatic digestibilities of bamboo fractions after pretreatment with aqueous ammonia were also observed. The results showed the potential of visible–near infrared spectroscopy in combination with multivariate analysis in efficiently analyzing the chemical composition and hydrolysabilities of lignocellulosic biomass, such as bamboo fractions.