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Abstract
BackgroundWoody plants with high glucose content are alternative bioresources for the production of biofuels and biochemicals. Various pretreatment methods may be used to reduce the effects of retardation factors such as lignin interference and cellulose structural recalcitrance on the degradation of the lignocellulose material of woody plants.ResultsA hydrogen peroxide-acetic acid (HPAC) pretreatment was used to reduce the lignin content of several types of woody plants, and the effect of the cellulose structural recalcitrance on the enzymatic hydrolysis was analyzed. The cellulose structural recalcitrance and the degradation patterns of the wood fibers in the xylem tissues of Quercus acutissima (hardwood) resulted in greater retardation in the enzymatic saccharification than those in the tracheids of Pinus densiflora (softwood). In addition to the HPAC pretreatment, the application of supplementary enzymes (7.5 FPU cellulase for 24 h) further increased the hydrolysis rate of P. densiflora from 61.42 to 91.94% whereas the same effect was not observed for Q. acutissima. It was also observed that endoxylanase synergism significantly affected the hydrolysis of P. densiflora. However, this synergistic effect was lower for other supplementary enzymes. The maximum concentration of the reducing sugars produced from 10% softwood was 89.17 g L−1 after 36 h of hydrolysis with 15 FPU cellulase and other supplementary enzymes. Approximately 80 mg mL−1 of reducing sugars was produced with the addition of 7.5 FPU cellulase and other supplementary enzymes after 36 h, achieving rapid saccharification.ConclusionHPAC pretreatment removed the interference of lignin, reduced structural recalcitrance of cellulose in the P. densiflora, and enabled rapid saccharification of the woody plants including a high concentration of insoluble substrates with only low amounts of cellulase. HPAC pretreatment may be a viable alternative for the cost-efficient production of biofuels or biochemicals from softwood plant tissues.
Highlights
Woody plants with high glucose content are alternative bioresources for the production of biofuels and biochemicals
Various pretreatment methods involving the usage of dilute acids, steam, organosolv, or sodium sulfite have been developed in the past to improve the efficiency of enzymatic saccharification for lignocellulose degradation
Organosolv and sulfite pretreatments have been reported to achieve high conversion rates for both hardwoods and softwoods [1, 16]. These results suggest that each pretreatment method is suitable for a particular type of lignocellulosic biomass in terms of reducing the lignin interference and the structural recalcitrance of cellulose
Summary
Woody plants with high glucose content are alternative bioresources for the production of biofuels and biochemicals. Woody plants are regarded as economically less feasible than agricultural residues (e.g., rice, wheat, and rapeseed straw) or biological waste materials (e.g., fruit peels, vegetables, and food ingredients) for bioenergy, Lee et al Biotechnol Biofuels (2021) 14:37 production due to degradation difficulties associated with the structural and chemical properties of plant cell walls Despite these difficulties, woody biomass may still be considered an attractive and renewable feedstock due to its high glucan content and abundance in nature [1]. Lignin is connected to hemicellulose, and coats microfibril units (ranging from 10 to 35 nm in diameter) including several elementary fibril groups comprised of β-1,4-glucose chain bundles [2,3,4] These microfibrils aggregate to form macrofibril structures (whose sizes range, e.g., between 0.5 and 2 μm for softwood kraft pulp), which in turn assemble to form primary and secondary tracheid cell walls and wood fibers in the xylem tissues of softwood or hardwood [4]. Various pretreatment methods involving the usage of dilute acids, steam, organosolv, or sodium sulfite have been developed in the past to improve the efficiency of enzymatic saccharification for lignocellulose degradation
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