Abstract
BackgroundConversion of plant cell walls to bioethanol and bio-based chemicals requires pretreatment as a necessary step to reduce recalcitrance of cell walls to enzymatic and microbial deconstruction. In this study, the sweet sorghum stems were subjected to various hydrothermal pretreatment processes (110°C to 230°C, 0.5 to 2.0 h), and the focus of this work is to systematically evaluate the degraded products of polysaccharides and lignins in the liquor phase obtained during the pretreatment process.ResultsThe maximum yield of xylooligosaccharides (52.25%) with a relatively low level of xylose and other degraded products was achieved at a relatively high pretreatment temperature (170°C) for a short reaction time (0.5 h). Higher temperature (>170°C) and/or longer reaction time (>0.5 h at 170°C) resulted in a decreasing yield of xylooligosaccharides, but increased the concentration of arabinose and galactose. The xylooligosaccharides obtained are composed of xylopyranosyl residues, together with lower amounts of 4-O-Me-α-D-GlcpA units. Meanwhile, the concentrations of the degraded products (especially furfural) increased as a function of pretreatment temperature and time. Molecular weights of the water-soluble polysaccharides and lignins indicated that the degradation of the polysaccharides and lignins occurred during the conditions of harsh hydrothermal pretreatment. In addition, the water-soluble polysaccharides (rich in xylan) and water-soluble lignins (rich in β-O-4 linkages) were obtained at 170°C for 1.0 h.ConclusionsThe present study demonstrated that the hydrothermal pretreatment condition had a remarkable impact on the compositions and the chemical structures of the degraded products. An extensive understanding of the degraded products from polysaccharides and lignins during the hydrothermal pretreatment will be beneficial to value-added applications of multiple chemicals in the biorefinery for bioethanol industry.
Highlights
Conversion of plant cell walls to bioethanol and bio-based chemicals requires pretreatment as a necessary step to reduce recalcitrance of cell walls to enzymatic and microbial deconstruction
The liquor pH The pH of the initial liquor before heating was 6.80, and it decreased to 3.13 with the increasing hydrothermal pretreatment (HTP) temperature and time (Table 1). This is expected that the hydronium ions released by the water during the HTP cause depolymerization of hemicelluloses by selective hydrolysis
Of glycosidic linkages, liberating O-acetyl group and other acid moieties to form various acids. The release of these acids is thought to catalyze the hydrolysis of hemicelluloses and oligosaccharides, resulting in more hemicelluloses that were degraded and solubilized in the liquor as the pretreatment temperature and time increased [14]
Summary
Conversion of plant cell walls to bioethanol and bio-based chemicals requires pretreatment as a necessary step to reduce recalcitrance of cell walls to enzymatic and microbial deconstruction. Sweet sorghum is considered as one of the potential renewable sources of energy for economic development and environmental sustainability, owing to its wide adaptability and high concentration of soluble sugars [3]. This plant could be effectively used as a source. HTP can result in structural changes of lignins and cellulose as well as solubilization of hemicelluloses, which in turn contribute to the improved enzyme accessibility in pretreated biomass [10]. It is necessary to characterize the degraded products in the liquors recovered during the HTP, which will enhance biorefinery viability in the future
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