网刊加载中。。。

使用Chrome浏览器效果最佳，继续浏览，你可能不会看到最佳的展示效果，

确定继续浏览么?

复制成功，请在其他浏览器进行阅读

Physicochemical and Morphological Variation of Bamboo Cell Wall During Hydrothermal Pretreatment

- ORCID：
Xiaojuan Yu ¹
✉
- ORCID：
Kai Fan ¹
- ORCID：
Xi Yao ²
- ORCID：
Meng Wang ³
- ORCID：
Kun Wang ¹
✉

1. MOE Engineering Research Center of Forestry Biomass Materials and Bioenergy, College of Materials Science and Technology, Beijing Forestry University, Beijing, 100083, China； 2. International Centre for Bamboo and Rattan, Beijing, 100102, China； 3. China National Pulp and Paper Research Institute Co., Ltd., Beijing, 100102, China

Updated：2022-01-20

DOI：10.1213/j.issn.2096-2355.2022.01.001

OUTLINE

Abstract

Pretreatment is important for achieving high-value utilization of biomass. This study is conducted to evaluate the destruction of the Moso bamboo cell wall via hydrothermal pretreatment at different temperatures and pH values. Compositional and morphological analyses and subsequent enzymatic hydrolysis of the solid fractions indicate that the destruction of the cell wall, instead of the degradation or removal of hemicellulose and lignin, or the configuration transition of the cellulose crystal structure, is the most critical aspect for improving bioconversion efficiency. Although only an 8%-10% weight loss is incurred and similar crystalline indexes are achieved after mild hydrothermal treatments, the recovery of glucose is doubled, whereas the recovery of xylose from pretreated samples is approximately 35%.

Keywords

bamboo; morphological variation; pretreatment; enzymatic hydrolysis

1 Introduction

Biomass is defined as all living organic matter that can be grown, including all plants, microorganisms, and animals, and is an important resource of renewable energy. The efficient development and utilization of biomass energy will facilitate the alleviation of the energy crisis and ecological environmental problems. The gradual increase in global energy consumption, fossil fuel depletion, and concerns regarding climate change have necessitated the development of sustainable energy systems based on renewable resources ^[

1]. Lignocellulosic biomass, as a natural polymer

resource, is suitable for the production of bio-based materials, including biofuels and chemicals. The plant cell wall primarily comprises cellulose, hemicellulose, and lignin, which are tightly linked through covalent, intermolecular, and intramolecular hydrogen bonds to form a complex three-dimensional structure that prevents biotransformation degradation. Pretreatment processes are extensively employed to release the cellulose component embedded in the heterogeneous matrix of the plant cell wall, which exhibits a high contact surface and hydrophilicity ^[

2]. Enzymatic hydrolysis and yeast fermentation can convert cellulose into bioethanol, whereas other chemical modification processes can yield cellulose-based derivatives. Hemicelluloses, as heteronuclear polysaccharides, are biodegradable into sugars or directly used for producing biomaterials, whereas lignin can be applied in chemical products owing to its unique renewable polymer, which contains numerous aromatic rings. Therefore, the efficient fractionation and targeted utilization of lignocellulosic resources benefit the renewable industry.

Bamboo is an important sustainable and renewable non-timber forest resource in China; it offers the advantages of abundant reserves, fast growth, high strength and hardness, superior processing performance, and local availability. Bamboo is a promising perennial plant that is distributed worldwide; it exhibits specific growth characteristics and features required for the production of natural materials. Bamboo fibers exhibit good physicochemical and mechanical properties; hence, they are a potential alternative to conventional materials used in polymer composites ^[

3]. Currently, bamboo is universally used in the industrial production of various bamboo-based composites, such as plywood, laminate, oriented strand board, and plastic composites, which are widely used as construction materials ^{[Reference 4

Baidu Scholar}4]. However, the substantial increase in labor and production costs has reduced the overall profit of the bamboo industry recently. Insufficient basic research and original innovation in bamboo science hinder the rapid development of the bamboo industry significantly. Therefore, the high-value utilization of all components in bamboo is crucial for its subsequent processing and development.

In recent years, researchers have investigated the mechanisms of various pretreatment techniques to enable the biodegradation of the cell wall; in this regard, significant progress has been achieved. Hydrothermal treatment with or without a catalyst, as a low-cost and environmentally friendly process, can partially separate hemicellulose and lignin from cellulose, disrupt the intact structure of lignocellulose, and improve the enzymatic bioconversion efficiency of cellulosic substrates. In this study, the complexity and diversity of the bamboo cell wall, as well as the corresponding variation during mild hydrothermal pretreatment (with or without acidic or alkaline catalyst) and bioconversion were emphasized. It is envisioned that the dissociation of non-cellulosic components and ultrastructural changes in different morphological regions will be established, thereby providing a theoretical foundation for the fractionation mechanism of bamboo fibers.

2 Experimental

2.1　Materials

Moso bamboo was harvested in Anhui Province; subsequently, it was airdried and crushed into powder. Between 40 and 60 meshes were allocated for chemical analysis and pretreatment. The bamboo was cut into small pieces (1 cm × 1 cm) and sliced to a thickness of 20 μm using a slicer (Yamato REM710, Japan) after being softened in a 90℃ water bath for approximately 20 d. All samples were stored in a 4℃ refrigerator, and all chemicals used in this study were of analytical grade and used directly.

2.2　Fractionation of bamboo

The powder samples were fractionated in a sealed stainless-steel autoclave (volume 50 mL) lined with polytetrafluoroethylene (PTFE). Five grams of bamboo powder or 20 pieces of bamboo slices were mixed with deionized water, 0.1 wt% H₂SO₄, and 0.1 wt% NaOH (labeled as P, P_H, and P_OH), respectively, at a solid-liquid ratio of 1∶10, where the raw material was completely immersed in the liquid. After tightening the reactor, the mixture was heated to the desired temperature (100℃, 120℃, and 140℃) and maintained for 3 h. Subsequ⁃ently, the reactor was removed promptly from the oven and cooled gradually to room temperature. Finally, the solid cellulosic fractions were accumulated via filtration, washed thoroughly with distilled water until a neutral pH value was achieved, and then freeze dried. The detailed parameters in addition to the corresponding designations of the samples are listed in Table 1.

Table 1 Yields and compositional analysis of fractionated samples

Samples	Temperature/℃	Solvent	Yield/%	Chemical components (relative content)/wt%
Samples	Temperature/℃	Solvent	Yield/%	Glc	Xyl	AIL	ASL
Raw material	—	—	—	40.7	23.5	34.1	1.7
P₁	100	H₂O	93.1	46.6	20.1	33.4	1.8
P₂	120	H₂O	93.9	45.3	19.6	35.1	1.6
P₃	140	H₂O	94.5	45.5	19.4	35.1	1.8
P_H1	100	0.1 wt% H₂SO₄	90.7	48.2	18.9	32.9	1.6
P_H2	120	0.1 wt% H₂SO₄	83.7	48.8	17.6	35.6	1.3
P_H3	140	0.1 wt% H₂SO₄	82.3	49.3	16.4	36.2	1.4
P_OH1	100	0.1 wt% NaOH	90.6	46.8	18.8	34.4	2.0
P_OH2	120	0.1 wt% NaOH	88.7	46.3	18.0	35.7	2.0
P_OH3	140	0.1 wt% NaOH	90.0	45.9	18.6	35.6	1.9

2.3　Compositional analysis

The composition of structural carbohydrates in the samples was determined based on the National Renewable Energy Laboratory Protocol and analyzed via high-performance liquid chromatography (HPLC, Waters e2695, USA) on an Aminex HPX-87H analytical column (300 mm × 7.8 mm, Bio-Rad Laboratories, USA). The analysis involved a two-step acid hydrolysis to determine the carbohydrate content, a weighing process to measure the content of acid-insoluble lignin (AIL, i.e., Klason lignin), and a spectral process to determine the content of acid-soluble lignin (ASL). The powder samples were hydrolyzed with 72% H₂SO₄ (by weight) for 1 h at room temperature with intermittent stirring and then diluted with pure water to 4%, followed by a hydrothermal treatment at 105℃ for another 2 h. Finally, the hydrolysate was directly analyzed via HPLC after being filtered using filter paper. The solid residue was oven dried to a constant weight and then used to calculate the content of acid-insoluble lignin ^[

5]. The acid-soluble lignin content was calculated using Equation (1) based on the absorbance at 205 nm using an ultraviolet (UV) photometer (Techcomp UV2310 II, China)

B = (A / 110) \cdot D

(1)

where B is the lignin content in hydrolysis solution, g/L; A is the UV adsorption at 205 nm; D is dilution factor; 110 is the absorbance factor, L/(g·cm).

2.4　Physicochemical structure analysis

The Fourier transform infrared (FT-IR) spectra of the selected samples were recorded on an FT-IR spectrophotometer (Bruker Tensor II, Germany) using the KBr disc method at a ratio of 100∶1; subsequently, the samples were ground to 74 μm to form a flake. The spectra were recorded in the absorption mode in the 500-4000 cm^-1 range at a resolution of 4 cm^-1. The X-ray diffractograms of the selected samples were recorded on an X-ray diffractometer (XRD, Bruker D8 advance, Germany) and scanned between 2θ of 5° and 35° using a goniometer at a scanning speed of 5°/min. The relative crystallinity was calculated as the ratio between the diffracted fraction from the crystalline region of the sample and the total diffraction from the cellulosic sample, using the following equation ^[

6].

C r I = (I_{002} - I_{a m}) / I_{002} \times 100 %

(2)

where CrI is the relative crystallinity, I₀₀₂ the diffraction intensity of the 002 plane, and I_am the diffraction intensity of the amorphous region.

Morphological changes in the cell wall of Moso bamboo before and after pretreatment and bioconversion were compared using optical and electronic techniques. After washing the bamboo slices thoroughly using deionized water, they were clamped onto slides using forceps and then shielded with coverslips to ensure the integrity of the slices before being observed under an optical microscope (Cewei LW300-28LT, China). After being airdried and sputtered with gold-palladium in a sputter coater (Hitachi SU8010, Japan), the original and pretreated samples were observed via scanning electron microscopy (SEM, S3400N, Hitachi, Japan) at an accelerating voltage of 5 kV.

2.5　Enzymatic hydrolysis of fractionated samples

The initial substrate (fractionated samples) concentration was set to 10% (w/V) in 30 mL of sodium acetate buffer (pH value 4.8) in a 100 mL conical flask, where 35 FPU/g of substrate loaded with enzyme (Novozymes Biotechnology Ltd., China) was introduced to a constant-temperature water-bath bed shaken at a rotating speed of 150 r/min at 30℃ for 72 h. The supernatant was sampled periodically for the following measurements after it was inactivated in a boiling water bath for 5 min ^[

7]. Each sample was filtered through a 0.22 μm filter and precisely diluted 20 times with deionized water. Glucose (Glc) and xylose (Xyl) were analyzed quantitivatvely via HPLC using an Aminex HPX-87H analytical column (300 mm × 7.8 mm) at 65℃, where 4 mmol/L H₂SO₄ was used as the eluent at a flow rate of 0.6 mL/min. Enzymatic hydrolysis was calculated as follows.

B E (%) = M_{G} / M_{C} \times 100 %

(3)

where BE is the bioconversion efficiency, M_G the amount of Glc released; M_C the amount of cellulose in substrate.

3 Results and discussion

3.1　Fractionation efficiency of mild pretreatment

Fractionation efficiency is typically regarded as the primary target for the pretreatment process and entire utilization of bamboo. Three parallel experiments for each condition were performed, and the standard deviations obtained for all data were less than 5% (Table 1). After hydrothermal treatment under mild conditions (P_1-3), only 6%-7% mass loss was detected in the solid residue, which implies low fractionation efficiency. The relative content of cellulose increased significantly as the hemicelluloses degraded partially and was then removed, as shown by compositional analysis. The addition of an acidic catalyst further improved the efficiency of hemicellulose removal because the hemicellulosic polysaccharides can be easily hydrolyzed into oligomers or monosaccharides by the action of acid ^[

8-9]. Accordingly, the relative contents of cellulose and lignin in the P_H1-H3 samples increased gradually with the pretreatment temperature. Because the yields of the solid product decreased, the increased mass losses were obtained under acidic conditions by calculating the recovery efficiency of the main components. The alkaline catalyst dissociated the covalent linkages between the hemicelluloses and lignin, as well as the intermolecular and intramolecular hydrogen bonds in cellulose. However, the low dosage of NaOH and temperature (100℃-140℃) in the current investigation limited the level of bond dissociation. Consequently, fragments with a certain molecular weight that could not be dissolved and removed were generated. Therefore, the yield of the pretreated samples (P_OH1-OH3) and main components were maintained at the same level. In summary, no significant changes in yield and composition were observed under mild pretreatment conditions, further confirming the reported results obtained from the compositional analysis of biomass at temperatures below 140℃ ^{[Reference 10

Baidu Scholar}10]. Combined with data from enzymatic hydrolysis, it was discovered that the destruction of the cell wall, instead of the degradation or removal of hemicelluloses and lignin, or the configuration transition of the cellulose crystal structure, was the most critical aspect for improving the bioconversion efficiency.

3.2　Physicochemical analysis of fractionated samples

By comparing the positions of the diffraction peaks in the XRD curves (Fig. 1), it was discovered that the crystal structure of the obtained cellulosic fractions did not change significantly after hydrothermal pretreatment. The typical cellulose I structure, which is assigned to the characteristic diffraction peaks at 2 $θ$ =16° and 22° for the 101 and 002 planes ^[

11], respectively, was clearly observed in all the samples. This is likely due to the partial degradation of amorphous hemicellulose during hydrothermal pretreatment as well as the relative increment in cellulose, which slightly enhanced the CrI of all P samples (33.2%-33.5%) from raw material (31.6%). By contrast, the diffraction peak at 2

θ

=22°, which is ascribed to the crystalline region in cellulose, became sharper after treatment was performed under acidic and alkaline conditions, corresponding to the increased CrI of all P_H (35.3%-36.7%) and P_OH (34.2%-35.6%) samples. Acidic hydrolysis can degrade hemicelluloses and amorphous cellulose into monosaccharides, thereby improving the proportion of crystalline cellulose. However, the higher CrI of the P_OH samples may be due to the significant dissolution and removal of hemicelluloses and lignin under alkaline conditions, although the configurational transition of cellulose crystals I to II was observed as well ^{[Reference 12

Baidu Scholar}12].

Fig. 1 X-ray diffractograms of raw material and fractionated samples under mild conditions

The variation in the functional groups in the fractionated samples was further examined using FT-IR technology (Fig. 2). Typical FT-IR adsorptions of lignocellulosic material were observed. The peak between 3400 and 3600 cm^-1 primarily originated from the stretching vibrations of hydroxyl groups that were either free or participating in the formation of intermolecular hydrogen bonds. The peak at 2922 cm^-1 is assigned to the stretching vibrations of C—H single bonds ^[

13]; the adsorption at 1733 cm^-1 is caused by carbonyl stretching vibrations of hemicelluloses ^{[Reference 14

Baidu Scholar}14]; and the absorptions at 1600, 1509, and 1426 cm^-1 are due to the stretching vibrations of the benzene ring (which exhibits an aromatic hydrocarbon structure), which are also the characteristic peaks of lignin ^{[Reference 15

Baidu Scholar}15]. The characteristic peak for the C—H vibration of the sugar end group was observed from 1000 to 1200 cm^-1, in which the stretching vibration of the glycosidic bond and the characteristic β-glycosidic linkage between the sugar units were identified at 1165 and 897 cm^-1, respectively ^{[Reference 16

Baidu Scholar}16]. Generally, the mild pretreatment processes did not change the FT-IR curves of all the samples. However, slight differences were observed during close examinations. The relative intensity of the peak for the carbonyl group weakened after hydrothermal treatment (particularly under alkaline conditions), indicating that the deacetylation reactions occurred chaotically. Additionally, the absorption at 1045 cm^-1, which is assigned to the characteristic peak of xylose, sharpened; this is likely due to the release of hemicellulosic fragments of small molecules from the extensive hydrolysis of hemicelluloses.

Fig. 2 FT-IR spectra of raw material and fractionated samples under mild conditions

3.3　Hydrolysis efficiency of fractionated samples

The modification of physicochemical properties observed in the cellulosic substrates can affect the subsequent bioconversion process. As shown in Fig. 3, the enzymatic conversion of all pretreated samples was significantly higher than that of the raw material. A low bioconversion efficiency (approximately 30% yield) even after 72 h of enzymatic hydrolysis was recorded because of the limited accessibility and anti-biodegradation of the cell wall in raw bamboo. The pretreatment partially destroyed the intact structure of the cell wall, as discussed above, which caused the efficiency of glucose released from the bioconversion process to be doubled. By contrast, a slight difference was discovered in the final bioconversion efficiency between the different pretreatment processes. The addition of the acid or alkali increased the yield of released glucose, partly because of the increased content of cellulose in the substrate. Another reason might be that the by-products generated under acidic or alkaline conditions might result in the inhibition of enzymes ^[

17]. In terms of the recovery of xylan, no xylose was detected in the enzymatic hydrolysis of the untreated feedstock, which is likely due to the lack of xylanase in the cocktail of enzymes and the original macromolecule of the hemicellulosic component. Interestingly, the release of xylose was increased significantly after the hydrothermal pretreatment, for which the highest value recorded was 35.4% for the P_H3 sample without xylanase. This indicates that a certain amount of hemicellulosic fragments were generated and then further degraded into xylose under weak acidic conditions during the bioconversion process, although the acidic pretreatment was not sufficient to fragment the hemicellulosic macromolecule into small molecules and then dissolve them ^{[Reference 18

Baidu Scholar}18]. By contrast, the alkaline aqueous solution, which is known to be an excellent solution for dissociating the linkages in lignin-carbohydrate complexes and dissolving hemicellulose and lignin, did not exhibit a positive effect on the recovery of xylose. It is shown that the alkaline pretreatment efficiency was lower than the acidic pretreatment efficiency under the same mild conditions. In addition, the morphological variation of the cell wall contributed significantly to the improvement in bioconversion.

Fig. 3 Effect of pretreatment conditions on recovery of glucose (a) and xylose (b) from fractionated samples after enzymatic hydrolysis

3.4　Morphological variation of Moso bamboo cell wall during pretreatment and biodegradation

As discussed above, the compositional analysis, cellulose crystal configuration, and functional groups did not change significantly during the mild pretreatment processes. Therefore, the significantly improved enzymatic efficiency was primarily ascribed to the morphological variation of the bamboo cell wall. The surface and cross-section of the raw and pretreated samples were recorded and compared (Fig. 4). It was observed that the surface of raw bamboo exhibited a relatively flat and smooth pattern, and the textural structure supported by the cellulose chain with inlaid amorphous hemicellulose was clearly shown ^[

19]. It has been reported that flakes of wax, pectin, and other components were attached to the surface of raw lignocellulosic materials ^{[Reference 20-21}20-21]. After pretreatment at 100℃, morphological changes had already occurred, as indicated by unbroken fibers and a few cracks. As the temperature was increased and catalyst added, considerable damage to the fibers was clearly observed. The surface was gradually coated with grooves and ridges, and some spherical droplets caused by lignin softening and agglomeration were observed on the surface ^{[Reference 22-23}22-23]. The relatively dense structure of the raw material was destroyed because some of the major components were degraded, removed, or relocated. Meanwhile, the loose and uneven surface of bamboo fibers facilitated the adsorption of cellulose and subsequent enzymatic hydrolysis, as shown above.

Fig.4 Optical and SEM images of bamboo slices before (first and second columns) and after pretreatment (third column) and enzymatic biodegradation (fourth column)

The cross-sectional view shows that the variations in the cell wall and cell corner middle lamella were pronounced. The cell walls were intact and organized neatly; meanwhile, the cellulose and hemicellulose aggregated primarily in the primary and secondary walls, and lignin was assembled in the secondary walls. Clearly, the integrity and arrangement of the bamboo cell walls remained after hydrothermal treatment at 100℃. Increasing the temperature to 140℃ induced the softening and loosening of the stable structure, and further thinned the cell walls by the addition of acid. As mentioned above, the mild alkaline condition did not effectively degrade or remove the non-cellulosic matrix; however, the swelling of the cell walls was reflected in the images. The bamboo slices were more severely damaged by the enzyme compared with by the pretreatment, and some intervals and indicators of destruction were observed in the raw bamboo after biological degradation. Results pertaining to the recovery of monosaccharides are shown in Fig. 3; as shown, some of the cell walls were completely destroyed and disappeared because of the degradation of cellulose into glucose, which is the framework of the plant cell. Furthermore, most regions of the cell wall disappeared in sample P_OH3; however, its bioconversion efficiency was low. This might be due to the swelling of cellulose to a certain degree that is sufficient for the generation of cell wall fragments by dissociating the cellulose chain, but not for the full degradation of cellulose into soluble oligomers.

4 Conclusions

In this study, hydrothermal pretreatment with or without acidic or basic catalysts was performed to change the compact structure of the Moso bamboo cell wall considerably such that the bioconversion efficiency of bamboo can be increased significantly. The compositional, physical, and morphological characteristics, as well as the enzymatic digestibility of the solid fractions of Moso bamboo, were compared. The data indicated that the content of the main components and the crystal configuration of cellulose remained the same under mild hydrothermal conditions; however, the recovery of glucose improved significantly from 30.2% to 63.6%. A maximum of 35% hemicellulose (represented as xylose) was dissolved and detected in the hydrolysate. Based on the morphological variation of the cell walls, it was concluded that the destruction of compact cell walls was the most important aspect for increasing both the accessibility of cellulase to cellulose and the bioconversion efficiency for bioenergy applications.

Acknowledgements

This study was supported by a grant from the Natural Science Foundation of China (No. 31770622).

References

Agbor V B, Cicek N, Sparling R, Berlin A, Levin D B. Biomass pretreatment: fundamentals toward application. Biotechnology Advances: An International Review Journal, 2011, 29(6), 675-685. [Baidu Scholar]

Lynd L R, Weimer P J, Zyl W H, Pretorius I S. Microbial cellulose utilization: fundamentals and biotechnology. Microbio⁃logy and Molecular Biology Reviews, 2002, 66(3), 506-577. [Baidu Scholar]

Divya D, Indran S, Bharath K N. Bamboo: A Potential Natural Material for Bio-composites. Berlin: Springer, 2020. [Baidu Scholar]

Gao J, Qu L, Qian J, Wang Z, He Z. Effects of combined acid-alkali and heat treatment on the physiochemical structure of Moso bamboo. Scientific Reports, 2020, DOI: 10.1038/s41598-020-63907-7. [Baidu Scholar]

Wang K, Xu F, Sun R. Molecular characteristics of Kraft-AQ pulping lignin fractionated by sequential organic solvent extraction. International Journal of Molecular Sciences, 2010, 11(8), 2988-3001. [Baidu Scholar]

Lin J, Ndlovu L M, Singh S, Pillay B. Purification and biochemical characteristics of β -D-xylanase from a thermophilic fungus Thermomyces lanuginosus. Biotechnology & Applied Biochemistry, 1999, 30(1), 81-87. [Baidu Scholar]

Yamashita Y, Shono M, Sasaki C, Nakamura Y. Alkaline peroxide pretreatment for efficient enzymatic saccharification of bamboo. Carbohydrate Polymers, 2010, 79(4), 914-920. [Baidu Scholar]

Yang H, Chen Q, Wang K, Sun R C. Correlation between hemicelluloses-removal-induced hydrophilicity variation and the bioconversion efficiency of lignocelluloses. Bioresource Technology, 2013, 147, 539-544. [Baidu Scholar]

Qin L, Liu Z H, Li B Z, Dale B E, Yuan Y J. Mass balance and transformation of corn stover by pretreatment with different dilute organic acids. Bioresource Technology, 2012, 112(1), 319-326. [Baidu Scholar]

Wang K, Yang H, Yao X, Feng X, Sun R C. Structural transformation of hemicelluloses and lignin from triploid poplar during acid-pretreatment based biorefinery process. Bioresource Technology, 2012, 116(4), 99-106. [Baidu Scholar]

Dong H L, Zhang A L, Lou R, Lou R, Xia C T. Effects of chemical pretreatment on the thermal-conversion properties of Moso bamboo. Paper and Paper Making, 2014, 33(11), 38-41. [Baidu Scholar]

Chen Q, Chen J, Wang K, Jiang J, Sun R. Research progress on the hydrothermal pretreatment of lignocellulosic biomass and its bioconversion. Scientia Silvae Sinicae, 2017, 53(9), 97-104. [Baidu Scholar]

Hayakawa K, Maruyama N, Fukasawa M. Capsule compri⁃sing low-substituted cellulose ether and method for preparing the same: US Patent, US20148784883 B2. 2014-07-22. [Baidu Scholar]

Gierlinger N, Goswami L, Schmidt M, Burgert I. In situ FT-IR microscopic study on enzymatic treatment of poplar wood cross-sections. Biomacromolecules, 2008, 9(8), 2194-2201. [Baidu Scholar]

Herrera R, Erdocia X, Llano-Ponte R, Labidi J. Characterization of hydrothermally treated wood in relation to changes on its chemical composition and physical properties. Journal of Analytical & Applied Pyrolysis, 2014, 107(5), 256-266. [Baidu Scholar]

Sun S, Sun S, Cao X, Sun R. The role of pretreatment in improving the enzymatic hydrolysis of lignocellulosic materials. Bioresource Technology, 2016, 199, 49-58. [Baidu Scholar]

Tang S, Xu C, Vu L, Liu S, Ye P, Li L, Wu Y, Chen M, Xiao Y, Wu Y. Enhanced enzymatic hydrolysis of Pennisetum alopecuroides by dilute acid, alkaline and ferric chloride pretreatments. Molecules, 2019, DOI: 10.3390/molecules24091715. [Baidu Scholar]

Huang L, Yang Z, Li M, Liu Z, Yao S. Effect of pre-corrected pH on the carbohydrate hydrolysis of bamboo during hydrothermal pretreatment. Polymers, 2020, DOI: 10.3390/polym12030612. [Baidu Scholar]

Hao S, Sun Y, Zhang D, Huang C, Ma X. Effects of hydrothermal pretreatment of different corn stalks for fermentable sugar production. Journal of Hebei University of Technology, 2016, 45(3), 85-92. [Baidu Scholar]

Song X, Jiang Y, Rong X, Wei W, Wang S, Nie S. Surface characterization and chemical analysis of bamboo substrates pretreated by alkali hydrogen peroxide. Bioresource Technology, 2016, 216, 1098-1101. [Baidu Scholar]

Wang K, Feng X, Sun R, Gwynn J L. Influence of incubation time on the physicochemical properties of the isolated hemicelluloses from steam-exploded lespedeza stalks. Industrial & Engineering Chemistry Research, 2010, 49(18), 8797-8804. [Baidu Scholar]

Kristensen J B, Thygesen L G, Felby J E. Cell-wall structural changes in wheat straw pretreated for bioethanol production. Biotechnology for Biofuels, 2008, DOI: 10.1186/1754-6834-1-5. [Baidu Scholar]

Li M F, Fan Y M, Xu F, Zhang X L. Cold sodium hydroxide/urea based pretreatment of bamboo for bioethanol production: Characterization of the cellulose-rich fraction. Industrial Crops and Products, 2010, 32(3), 551-559. PBM [Baidu Scholar]

Physicochemical and Morphological Variation of Bamboo Cell Wall During Hydrothermal Pretreatment

Abstract

Keywords

1 Introduction

2 Experimental

2.1 Materials

2.2 Fractionation of bamboo

2.3 Compositional analysis

2.4 Physicochemical structure analysis

2.5 Enzymatic hydrolysis of fractionated samples