Hydrolysis Patterns of Xylem Tissues of Hardwood Pretreated With Acetic Acid and Hydrogen Peroxide

Abstract

The structural recalcitrance of lignocellulose limits its enzymatic hydrolysis, which leads to inefficient enzyme usage and inhibition of saccharification, depending on the pretreatment method. Research on the structural properties of xylem tissues of hardwood and their effect on enzymatic saccharification is necessary to achieve cost-effective biofuel production via improved enzyme cocktail preparation. Oak wood (Quercus acutissima) was pretreated and delignified with a hydrogen peroxide-acetic acid (HPAC) solution. Cellulose was found to undergo significant swelling in the lumen of the wood fiber, and it was sorted into readily hydrolysable (72.9%), mid-hydrolysable (8.2%), and hardly hydrolysable (18.9%) cellulose forms. Oak wood has been shown to be strongly retarded among the various types of hardwoods. The recalcitrance of the xylem tissues, such as wood fibers, tracheids, vessel elements, and ray parenchyma cells, was determined through analysis of the hydrolysis rates. It was found to increase in the following order: ray parenchyma cells < tracheids < wood fibers or vessel elements < tracheids < wood fibers. The wood fibers were almost enzymatically fragmented into pieces ∼90 µm in length at crack sites in 6 h. The wood fibers were digested faster in the S 3 or S 2 wall than in the primary wall. The result indicated that the primary wall may be a structural retardation factor in the hardwood as sorted to the hardly hydrolysable cellulose. In presence of 10% substrate supplemented with enzymes to reduce the structural recalcitrance (xylanase and lytic polysaccharide monoxygenase) and end-product inhibitions (beta-glucosidase), the hydrolysis rate was increased by 55.21%. Ethanol fermentation exhibited a higher efficiency when a single substrate (Q. acutissima) rather than a mixture of various hardwoods was used. Of all the xylem tissues of hardwood that were delignified by HPAC pretreatment, wood fiber was found to be a structural retardation factor owing to the recalcitrance its primary wall. Thus, enzyme preparation can enable the rapid and efficient hydrolysis for the commercialization of bioethanol from hardwood.

Hydrolysis pattern analysis of xylem tissues of woody plants pretreated with hydrogen peroxide and acetic acid: rapid saccharification of softwood for economical bioconversion

“…The structural modification of the crystalline form from cellulose I α to cellulose III 1 induced greater adsorption of Cel7A in the cellulose hydrophobic region, and accelerated the hydrolysis of the crystalline cellulose [ 22 ]. Morphology change of wood fiber of hardwood by HPAC pretreatment was observed as more cellulase-friendly cellulose (cellulose II or III) causing remarkable cellulose swelling in the lumen site of the wood fiber compared to acidified sodium chlorite (ASC) pretreatment, which was sorted into readily hydrolysable (72.9%), mid-hydrolysable (8.2%), and hardly hydrolysable (18.9%) cellulose forms [ 23 ]. In Fig.…”

“…The shortened fibers remained intact during the prolonged 24-h incubation. The remaining fragments at the late stage included more recalcitrant cellulose fibers that were resisted cellulase action, implying that the primary wall or S 1 layer of wood fiber was responsible for this result [ 23 ]. These results may thus explain the retardation of Q. acutissima degradation compared to that of P. densiflora .…”

HPAC Pretreatment Facilitates Enzymatic Hydrolysis of Softwood

“…The shortened bers remained intact during the prolonged 24-h incubation. The remaining fragments at the late stage included more recalcitrant cellulose bers that were resisted cellulase action, implying that the primary wall or S 1 layer of wood ber was responsible for this result [18]. These results may thus explain the retardation of Q. acutissima degradation compared to that of P. densi ora.…”

“…Hydrolysis patterns of these substrates at the macromolecular level were also different from each other. Based on the results, P. densi ora was chosen to achieve rapid sacchari cation at a highly insoluble substrate, instead of Q. acutissima which showed greater recalcitrance during the late stage of hydrolysis [18].…”

Synergistic Treatment of Alkali Lignin via Fungal Coculture for Biofuel Production: Comparison of Physicochemical Properties and Adsorption of Enzymes Used As Catalysts

“…The hydrolysis efficiency of Avicel was evaluated by the yield of reducing sugar. The yield of reducing sugar was determined by the 3,5-dinitrosalicylic acid method (Lee et al, 2020).…”