假木质素沉积及对纤维素酶解的影响研究进展

doi:10.11707/j.1001-7488.20200314

Abstract

Abstract:

Lignocellulosic biomass is one of the most abundant renewable resources on earth. In order to improve the conversion rate of lignocellulosic biomass, increase the enzymatic hydrolysis efficiency of cellulose and the yield of fermentable sugars and to reduce the usage of cellulase and the conversion cost of biomass, it is essential to obtain the pretreated lignocellulosic biomass. However, the natural barrier between lignin, cellulose and hemicellulose limits the availability of cellulase to the cellulose components encapsulated inside. The main pretreatment methods of lignocellulose covered physical method, chemical method, physical chemical method and biological method. At present, the more adopted pretreatment methods include the dilute acid(hydrochloric acid, sulfuric acid, nitric acid, etc.)with the mass fraction less than 4% at the temperature of 120-210℃, high temperature hot water method, steam explosion method and liquid hydrothermal method. The dissolution and removal of lignin or most of the hemicellulose by various pretreatment methods is beneficial to improve cellulase accessibility. At present, a large number of studies have shown that lignin can significantly inhibit the enzymatic hydrolysis of cellulose, pretreatment can reduce lignin content and improve the efficiency of cellulose hydrolysis. In recent years, studies have shown that the relative content of Klason lignin would increase after the pretreatment of lignocellulose under severe conditions by using dilute acid and high temperature water. During the pretreatment processes of lignocellulosic biomass, lignin droplets may be deposited on the surface of the cellulose in the form of pseudo-lignin, so that it can inhibit cellulase hydrolysis more than natural lignin. However, no relevant review paper was found in the published articles. In this paper, the formation processes of lignin droplets and pseudo-lignin during the pretreatment of biomass were described. The possible mechanisms of pseudo-lignin production were put forward, and its composition and properties were reviewed. On this basis, the effects of lignin droplets and pseudo-lignin on the enzymatic hydrolysis of lignocellulose were summarized. Finally, the effects of lignin droplet and pseudo-lignin on the enzymatic hydrolysis of cellulose were discussed, and then the regulation strategy of pseudo-lignin formation was summarized. The authors believe that it is of great significance to study the mechanisms, structure characteristics, regulation mechanisms of the production of pseudo-lignin in the process of biorefinery. The formation of pseudo-lignin is a heterogeneous reaction process. At the same time, the formation mechanisms of pseudo-lignin can be studied from the mesoscale behavior due to the influence of mass transfer(molecular level)and the flow(macroscopic statistical level), and at the same time, the related models and theories should be established to realize their scientific quantitative descriptions and regulation. Moreover, it is beneficial to the development of lignocellulosic biomass refining processes and also it is conducive to promote the formation and development of an interdisciplinary scale of science.

Key words: lignocellulose, pseudo-lignin, cellulase, biomass

CLC Number:

TQ35

Ruyi Sha,Shasha Zhang,Zhan Yu,Fuquan Zhao,Chenggang Cai,Zhuqian Xiao,Jianwei Mao. Advances in Pseudo-Lignin Deposition and Its Effects on Enzymatic Hydrolysis of Cellulose[J]. Scientia Silvae Sinicae, 2020, 56(3): 127-143.

Figures/Tables 5

Table 1

Lignin droplets of different raw materials under different pretreatment conditions"

样品 Sample	预处理条件 Pretreatment conditions	分析和表征方法 Analysis and characterization methods	主要现象或观点 Main phenomena or viewpoints	参考文献 Reference
玉米秸秆 Maize stover	0.8% H₂SO₄(W/W)，150 ℃，20 min	SEM、TEM、FTIR、NMR、抗体标记、细胞化学染色 SEM，TEM，FTIR，NMR，antibody labeling, cytochemical staining	温度达到木质素相转变温度引起木质素凝聚成较大的熔融体，在细胞壁内外迁移，并沉积于细胞壁表面 Thermochemical pretreatments reaching temperatures above the range for lignin phase transition cause lignins to coalesce into larger molten bodies that migrate within and out of the cell wall, and can redeposit on the surface of plant cell walls	Donohoe et al., 2008
甘蔗渣 Sugarcane bagasse	1% H₂SO₄(V/V)， 120 ℃，20 min +0.25%~4% NaOH(W/V)，120 ℃，40 min	共聚焦激光扫描显微镜(CLSM)、荧光寿命成像显微术(FLIM) Confocal laser scanning microscopy (CLSM)， fluorescence lifetime imaging microscopy (FLIM)	酸预处理使得木质素分布于细胞壁外边缘，排列紊乱；碱处理有利于清除蔗渣纤维中间的木质素；木质素荧光衰减时间与其在细胞壁内的分布量具有强相关性 The acid pretreatment caused a disorder in the arrangement of lignin and its accumulation in the external border of the cell wall. The alkali pretreatment efficiently removed lignin from the middle of the bagasse fibers. A strong correlation between the decay times of the lignin fluorescence and its distribution within the cell wall	Coletta et al., 2013
玉米茎 Maize stems	2%H₂SO₄(W/W)， 150 ℃，20 min	SEM、原子力显微镜(AFM) SEM, atomic force microscopy (AFM)	在中性和酸性条件下，＞130 ℃时产生木质素液滴，主要含有木质素和木质素碳水化合物复合物 Droplets are produced from corn stover during pretreatment under neutral and acidic pH at and above 130 ℃, composed of lignins and lignin carbohydrate complexes	Selig et al.， 2007
竹子 Bamboo	170 ℃，20 min，油浴Oil bath	FTIR，XPS	竹片水解过程中，竹片内部木质素类物质会迁移至竹片表层和表面 The interior lignin would gradually migrate to the bamboo surface during the pre-hydrolysis	林玲等，2014
柳枝稷 Panicum virgatum	1% H₂SO₄，25 ℃，4 h；1% H₂SO₄，160 ℃，30 min(6 ℃·min^-1)	小角度中子散射(SANS) Smallangle neutron scattering (SANS)	稀酸预处理增加结晶纤维素纤维的横截面半径，形成平均半径135 Å的木质素共聚物 Dilute acid pretreatment increases the cross-sectional radius of the crystalline cellulose fibril. This change is accompanied by the formation of R_g~135 Å lignin aggregates	Pingali et al., 2010
小麦秸秆 Wheat straw	180~200 ℃，10~20 min，料水比Ratio of material and water 1:10	荧光显微镜 Fluorescence microscope	高温预处理导致样品次生壁大量断裂，可能为木质素进入细胞腔提供通道 Pretreated at high temperature also exhibited numerous fractures in the secondary walls that might have served as passages for lignin into the cell lumen	Holopainen-Mantila et al., 2013
小麦秸秆 Wheat straw	80 ℃浸泡6 min，195 ℃蒸汽中保持6 min Soak in 80 ℃ for 6 min, and keep in 195 ℃ steam for 6 min	SEM，AFM，ATR-FTIR	高温预处理使得木质素液滴重新分布，从而增加纤维素的可利用度 High temperature pretreatment makes lignin droplets redistributed, thus increasing the availability of cellulose	Kristensenet al.,(2008)
杨木 Poplar wood	180 ℃，11~70 min，5%(W/V)	单克隆抗体免疫标记、凝胶层析 Monoclonal antibodies，gel chromatography	糖组学分析结果表明可以监控木质素碳水化合物的复合物，如木质素-果胶/阿拉伯聚糖/木聚糖等，即便是最温和的水热预处理也可以打乱其结构 Glycome profiling studies monitor the structure of lignin carbohydrate complex，such as lignin-pectins and arabinogalactans/xylan, even under mild hydrothermal pretreatment conditions	et al.,(2011)
杨木 Poplar wood	200 ℃，15 min，10%(W/W)	SEM、湿化学分析、NMR SEM，wet chemical analysis，NMR	在共热预处理过程中，源于杨木的木质素液滴能够迁移到纤维素Avicel的表面，明显阻滞纤维素的水解 Lignin droplets from poplar wood relocated onto the Avicel surface by hydrothermal pretreatment, significantly impeded cellulose hydrolysis	Liet al.,(2014a)
松木 Pine wood	175 ℃，8.5×10⁵~10.0×10⁵ Pa，85 min	CP/MAS¹³C NMR，FTIR	自水解预处理后酸不溶性木质素含量从32.06%增加至46.11%，可能与半纤维素损失和木质素液滴形成有关 The acid insoluble lignin increased from 32.06% to 46.11% by autohydrolysis pretreatment, which can be attributed to the hemicellulose loss and the formation of pseudo-lignin during autohydrolysis process	Haoet al.,,(2017)
挪威云杉 Picea abies	260 ℃，8 min	FTIR，NMR，Py-GC/MS	经预处理(260 ℃，8 min)后，木质素含量由27.9%增加至30.4%，很可能与半纤维素参与形成新的木质素有关 After pretreatment (260 ℃, 8 min), the content of lignin increased from 27.9% to 30.4%, which may be related to the participation of hemicellulose in the formation of new lignin	Normark et al., 2016

Table 1

Table 2

Changes of lignin content of different raw materials after pretreatment"

样品 Sample	预处理条件 Pretreatment conditions	预处理前 Before pretreatment		预处理后 After pretreatment		主要现象或观点 Main phenomena or viewpoints	参考文献 Reference
样品 Sample	预处理条件 Pretreatment conditions	总纤维 Total fiber (%)	木质素 Lignin (%)	总纤维 Total fiber (%)	木质素 Lignin (%)	主要现象或观点 Main phenomena or viewpoints	参考文献 Reference
毛果杨 Populus trichocarpa	0.5% H₂SO₄，170 ℃， 0.3~26.8 min，5%(W/W)	75.4	24.6	68~75	~25	稀酸预处理并没有去除木质素，显著降低半纤维素的含量 Dilute acid pretreatment did not remove lignin and significantly reduced the content of hemicellulose	Caoet al.,(2012)
玉米秸秆 Maize straw	0.5% H₂SO₄，160 ℃， 20 min	36.0	17.2	59.2	26.8	预处理后半纤维素含量明显下降，木质素含量增加 After pretreatment, hemicellulose content decreased and lignin content increased	Maoet al.,(2010)
柳枝稷 Panicum virgatum	0.1 mol·L^-1 H₂SO₄， 160 ℃，2.5 min	~42	~30	~42	~48	稀酸预处理并没有去除木质素，假木质素的产生可能使得木质素含量测定值增大 Dilute acid pretreatment did not remove lignin, and the production of pseudo-lignin may increase the measurement value of lignin content	Fostonet al.,(2010)
柳枝稷 Panicum virgatum	0.1 mol·L^-1 H₂SO₄， 160 ℃，60 min	~42	~30	~25	~75
杨木 Poplar wood	0.1 mol·L^-1 H₂SO₄， 160 ℃，2.5 min	~50	~28	~60	~35
杨木 Poplar wood	0.1 mol·L^-1 H₂SO₄， 160 ℃，60 min	~50	~28	~52	~44
柳枝稷 Panicum virgatum	190 ℃，0.05 g H₂SO₄g^-1生物质，1 min，25%固含量190 ℃， 0.05 g H₂SO₄g^-1 biomass，1 min，25% solid content	76.4	22.7	62.8	32.1	预处理后，非木质素类原料有助于Klason木质素含量的增加 After pretreatment, non lignin materials contribute to the increase of Klason lignin content	Samuelet al.,(2010)
甘蔗渣 Sugarcane bagasse	110 ℃，30 min，自水解 110 ℃，30 min，autohydrolysis	56.3	31.9	63.6	30.9	剧烈的自水解预处理后木质素含量增加可能是因为大量半纤维素的去除而保留了大部分木质素 The increase of lignin content after autohydrolysis pretreatment may be due to the removal of large amount of hemicellulose and the retention of most of lignin	Hashmiet al.,(2017)
	190 ℃，10 min，自水解 190 ℃，10 min，autohydrolysis	56.3	31.9	55.9	41.8
	205 ℃，6 min，自水解 205 ℃，6 min，autohydrolysis	56.3	31.9	55.0	39.4
松木 Pine wood	175 ℃，8.5×10⁵~10.0×10⁵ Pa，85 min	58.5	49.7	32.1	46.1	酸不溶性木质素含量增加可能源自半纤维素的损失或者假木质素的形成 The increase of acid insoluble lignin content may result from the loss of hemicellulose or the formation of pseudo-lignin	Haoet al.,(2017)
玉米秸秆 Maize straw	1.5 MPa，8 min，5%氨水 1.5 MPa，8 min，5% ammonia	61.4	6.83	45.7	11.3	氨化汽爆处理对纤维素含量改变不大，却使木质素增加，这可能是由于汽爆过程中产生“假木素” Steam-explosion of ammoniation has little effect on cellulose content, but increases lignin content, which may be due to the production of “pseudo-lignin” in the process of steam explosion	杨雪霞等, 2001
玉米秸秆 Maize straw	1.5 MPa，8 min，15%氨水 1.5 MPa，8 min，15% ammonia	61.4	6.83	44.1	12.4		杨雪霞等, 2001
玉米秸秆 Maize straw	160 ℃，20 min， 0.5% H₂SO₄	28.6	17.2	69.2	22.2	SEM表明预处理样品表面有木质素液滴的沉积 SEM showed that there was a deposition of lignin droplets on the surface of the pretreated samples	Singh et al., 2015
挪威云杉 Picea abies	260 ℃，8 min	60.6	27.9	64.2	30.4	Klason木质素含量增加源自于碳水化合物，而不是木质素，可能形成了假木质素 The increase in Klason lignin content is due to carbohydrates, not lignin, which may form pseudo-lignin	Normark et al., 2016
挪威云杉 Picea abies	310 ℃，25 min	60.6	27.9	1.9	93.0
杨木综纤维素 Hybrid poplar holocellulose	0.1 mol·L^-1 H₂SO₄， 170 ℃，40 min	89.0	8.2	64.8	31.8	预处理后产生大量的假木质素，完全来自于碳水化合物 A large number of pseudo-lignin was produced after pretreatment, which are completely derived from carbohydrates	Sannigrahi et al., 2011

Table 2

Fig.1

Table 3

Pseudo-lignin formation after pretreatment with different raw materials"

样品 Sample	预处理条件 Pretreatment conditions	假木质素表征 Characterization of pseudo-lignin	假木质素结构信息 Pseudo-lignin structural information	主要现象或观点 Main phenomena or viewpoints	参考文献 Reference
挪威云杉 Picea abies	310 ℃，25 min	FTIR，NMR， Py-GC/MS	假木质素有助于色谱中C信号增强，而不是木质素苯丙烷基单元相关的G、S和H信号 Pseudo-lignin contributes to the enhancement of C signal in chromatography, rather than the G, S and H signals related to the phenylpropyl units of lignin	最剧烈的烘焙条件下(310 ℃，25 min)产生了假木质素，离子液体[C₄C₁im][MeCO₂]能够溶解假木质素，打乱结构，有利于酶解 The most severe torrefaction conditions (310 ℃, 25 min) resulted in increase of the Klason lignin value, pretreatment using ionic liquid [C₄C₁im][MeCO₂] a way forward for dissolving the pseudo-lignin, disrupting the structure, is conducive to enzymatic hydrolysis	Normark et al., 2016
硬木 Hardwood	180~210 ℃， 5~15 min	SEM，FTIR，TG	含有甲氧基和脂肪族羟基，T_g(170~180 ℃) Containing methoxy group and aliphatichydroxyl groups，T_g(170~180 ℃)	在预处理后木材表面和内部观察到球形木质素或假木质素 Spherical lignin or pseudo-lignin were observed on the surface and inside of wood after pretreatment	Ko et al., 2015
赤桉 Eucalyptus camaldulensis	0.02 mol·L^-1 AlCl₃， 140~180 ℃	SEM，2D-HSQC NMR，FTIR，XRD	浓缩S型木质素单体大约出现于δ_C/δ_H 105.3/6.45，确切的结构信息不明确 The condensed S-type lignin unit was presented around δ_C/δ_H 105.3/6.45.The exact structural information is not clear	木质素回收率超过100%，部分Klason木质素为假木质素，呈球形分布 The lignin recovery in the pretreated substrates was over 100%, suggesting that partial Klason lignin actually was pseudo-lignin, distributing as spheres	Shen et al., 2016
玉米皮 Maize stem rind	120~200 ℃， 2~4 ℃·min^-1	FTIR，SEM	游离微球表面含有大量CC和CO键等木质素类结构 Many CC and CO bonds similar to the functional groups of lignin were identified on the surface of the free microspheres	假木质素呈游离态和吸附态微球，180 ℃时游离态含量最高，微球的形状随预处理温度改变而变化，吸附型形成的温度范围较广 The pseudo-lignin is free and adsorbed microsphere. The content of the free state is the highest at 180 ℃. The shape of the microspheres changes with the pretreatment temperature, and the temperature range of the formation of the adsorption type is wide	Yang et al., 2015
小麦秸秆 Wheat straw	蒸汽自水解，170~ 200 ℃，lg R₀= 3.1~4.4 Autohydrolysis， 170~200 ℃，lg R₀=3.1~4.4	SEM	假木质素的形成降低了木质素的比表面积 The formation of pseudo-lignin reduces the specific surfacearea of lignin	球状假木质素在较剧烈的条件下(lg R₀≥4.10)较易沉积 Globular pseudo-lignin is easy to deposit under the higherseverities(lg R₀≥4.10)	Sipponen et al., 2014a
北美鹅掌楸 Liriodendron tulipifera	高压热水(200 ℃， 15 min)，过氧乙酸 (90 mmol·L^-1， 60 ℃，6 h) Hot compressed water(200 ℃， 15 min)，peracetic acid(90 mmol·L^-1， 60 ℃，6 h)	XRD，FTIR，SEM	形成的假木质素液滴尺寸＜2 μm Droplet size of formed pseudo-lignin＜2 μm	生物质表面形成球状假木质素液滴，可以被过氧乙酸清除掉 Spherical pseudo-lignin droplets formed on the surface of biomass can be removed by peracetic acid	Lee et al., 2017
桉树 Eucalyptus	170~210 ℃， 0.5 h，then 2% NaOH，80 ℃，2 h	2D-HSQC NMR、 31P NMR、共焦显微拉曼光谱、SEM 2D-HSQC NMR， 31P NMR，confocal Raman microscopies, SEM	木质素组分M_w 3 640~4 610 g·mol^-1，M_n 2 760~3 640 g·mol^-1。 Lignin components M_w 3 640~ 4 610 g·mol^-1，M_n 2 760~3 640 g·mol^-1	温度增加到210 ℃，木质素含量降低可能与碳水化合物和木质素降解产物相结合形成假木质素有关 When the temperature increased to 210 ℃, the decrease of lignin content may be related to the combination of carbohydrate and lignin degradation products to form pseudo-lignin	Wanget al.,(2017)
欧洲山杨 Populus tremula	蒸汽爆破，185~220 ℃，5~15 minSteam explosion，185~220 ℃，5~15 min	2D HSQC	源于碳水化合物中的假木质素的信号，不干扰侧链木质素信号 The signal derived from the pseudo-lignin in carbohydrate does not interfere with the signal of side chain lignin	形成的假木质素可能源于碳水化合物，可溶于二氧六环水溶液，含量占原料总质量的5%~8% The pseudo-lignin can be derived from carbohydrate and soluble in dioxane-water solution, accounting for 5%-8% of the total mass of raw materials	Li et al., 2007
综纤维素 Holocellulose	180 ℃，0.1~0.2 mol·L^-1 H₂SO₄， 40~60 min	GPC，FTIR， ¹³C NMR	假木质素M_w ~5 000 g·mol^-1，M_w~1 000 g·mol^-1，含有羰基、羧基、甲氧基和芳香基 Pseudo-lignin(M_w~5 000 g·mol^-1，M_w~1 000 g·mol^-1，containing carbonyl, carboxyl, methoxy and aromatic groups	假木质素含有的羰基、羧基、芳香族和脂肪族结构单元源于纤维素和半纤维素 The structural units of carbonyl, carboxyl, aromatic and aliphatic in pseudo-lignin are derived from cellulose and hemicellulose	Hu et al., 2012
脱木质素杂交杨木 Hybrid poplar	0.1 ~0.2 mol·L^-1 H₂SO₄，160~180 ℃，5~60 min	FTIR，NMR，SEM	含有芳香基，甲氧基和糖基功能团 Contains aromatic, methoxy and glycosyl functional groups	假木质素可由生物质中的酸催化碳水化合物脱水转变而成，而木质素的贡献率不明显 Pseudo-lignin can be formed by dehydration of carbohydrate catalyzed by acid in biomass, but the contribution rate of lignin is not obvious	Sannigrahi et al., 2011
欧美杨 Populus euramericana	170 ℃，1 h，液体热水 170 ℃，1 h，liquid hot-water	SEM	冷却诱导假木质素含有降解的木质素、糠醛和羟甲基糠醛 Cooling induced pseudo-lignin contains degraded lignin, furfural and HMF	预处理冷却过程中，溶解于水解液中的非糖类有机物沉积于预处理木材表面形成冷却诱导假木质素 During the cooling process of pretreatment, the non carbohydrate organic matter dissolved in the hydrolysate deposited on the surface of pretreatment wood to form cooling induced pseudo-lignin	Zhuanget al.,(2017)
杨木 Poplar wood	蒸汽爆破，190~205 ℃，0~10 minSteam explosion，190~205 ℃，0~10 min	数学模型模拟 Mathematical model simulation	/	假木质素形成模型为酸水解中木聚糖解聚和醋酸中木质素溶解、浓缩2个一级反应动力学模型的结合，模型中引入糠醛和木质素聚合2个旁路反应 The model of pseudo-lignin formation is a combination of two first-order reaction kinetic models, i.e. the depolymerization of xylan in acid hydrolysis and the dissolution and concentration of lignin in acetic acid. An additional reaction pathway including the furfural and lignin polymerization is introduced to form a new model	Sui et al., 2009

Table 3

Table 4

Structural components and characteristics of pseudo-lignin with different biomass materials"

类别 Category	生物质 Biomass	原料的化学组成 Chemical composition of raw materials			原料的构造特点 Structural characteristics of raw materials	假木质素特征 Characteristics of pseudo-lignin	参考文献 Reference
类别 Category	生物质 Biomass	纤维素 Cellulose (wt%)	半纤维素 Hemicellulose (wt%)	木质素 Lignin (wt%)	原料的构造特点 Structural characteristics of raw materials	假木质素特征 Characteristics of pseudo-lignin	参考文献 Reference
阔叶材 Hardwood	赤桉 Eucalyptus camaldulensis	43.5	17.1	26.3	甘露糖(0.8%)、葡萄糖(43.5%)、木糖(15.7%)、半乳糖(0.6%)、木质素(26.3%)和乙酰基团(3.94%)等，结晶指数(CrI)32.1% Mannose (0.8%), glucose (43.5%), xylose (15.7%), galactose (0.6%), lignin (26.3%) and acetyl group (3.94%), crystal index (CrI) 32.1%	预处理后(140~180 ℃)，克拉森木质素含量由32.4%增加至51.6%，可能部分为假木质素，SEM结果表明假木质素以球形液滴的形式分布于预处理后的赤桉表面 After pretreatment (140-180 ℃), the content of Klason lignin increased from 32.4% to 51.6%, which may be partially pseudo-lignin. SEM results showed that pseudo-lignin distributed on the surface of Eucalyptus camaldulensis in the form of spherical droplets	Shen et al., 2016
	北美鹅掌楸 Liriodendron tulipifera	39.0	18.8	21.7	阿拉伯糖(1.9%)、甘露糖(2.0%)、半乳糖(4.9%)和酸可溶性木质素(5.6%)等，结晶指数(CrI)60.8% Arabinose (1.9%), mannose (2.0%), galactose (4.9%) and acid soluble lignin (5.6%), etc. the crystal index (CrI) was 60.8%	水热预处理后，在表面形成不同直径(＜2 mm)的球形液滴——假木质素 After hydrothermal pretreatment, pseudo-lignin with different diameter (< 2 mm) was formed on the surface of hardwood	Lee et al., 2017
	桉树 Eucalyptus	39.5	21.5	29.5	含25.5%酸不溶性木质素和4.0%的酸可溶性木质素，分离得到的木质素M_w为3 630，M_n为2 760，M_w/M_n为1.32 It contains 25.5% acid insoluble lignin and 4.0% acid soluble lignin. The isolated lignin was M_w 3 630, M_n 2 760 and M_w/M_n 1.32	温度增至210 ℃，木质素组分的得率下降至2.7%，可能与假木质素形成有关，此时分离得到的木质素M_w为3 630，M_n为2 780，M_w/M_n为1.31 When the temperature increased to 210 ℃, the yield of lignin component decreased to 2.7%, which may be related to the formation of psondo-lignin. At this time, the separated lignin was M_w 3 630, M_n 2 780, and M_w/M_n 1.31	Wanget al.,(2017)
	欧洲山杨 Aspen wood	/	/	20.1	2D HSQC NMR表明杨木磨木木质素中的β-O-4′结构数值为54%，非常接近于桦树(60%) 2D HSQC NMR showed that the value of β-O-4′ structure was 54%, very close to that of birch (60%)	经蒸汽预处理后，产生5%~8%的假木质素，可溶解于二氧六环/水(9:1)中；二维核磁脉冲HSQC揭示源于碳水化合物的假木质素信号 After steam pretreatment, about 5%-8% of the pseudo-lignin are produced, which can be dissolved in dioxane/water (9:1); two dimensional NMR pulse HSQC reveals the signal of pseudo-lignin from carbohydrates	Li et al., 2007
	脱木质素杂交杨木 Hybrid poplar	67.2	21.8	8.2	综纤维素原料，含有1.6%克拉森木质素和6.6%的酸可溶性木质素 The raw material of holocellulose contains 1.6% Klason lignin and 6.6% acid soluble lignin	酸预处理后(CS=3.27)，假木质素以液滴状或球状覆盖在生物质表面；HMF和呋喃可能会与葡萄糖、木糖或降解产物成键而形成假木质素；假木质素形成量为25%~94% After acid pretreatment (CS=3.27), pseudo-lignin was covered on the surface of biomass in droplets or spheres; HMF and furan may form bonds with glucose, xylose or degradation products to form pseudo-lignin; the amount of pseudo-lignin formation was about 25%-94%	Sannigrahi et al., 2011
	欧美杨 Populus euramericana	/	/	/	木片厚度5 mm Wood chip thickness 5 mm	液体热水预处理的冷却阶段，假木质素形成量为19.6 mg·g^-1原料，冷却诱导的假木质素含有木质素寡聚物(71.46%)、呋喃(9.44%)、羟基苯甲酸(5.19%)、HMF(1.18%)、香草醛(1.42%)、丁香醛(1.89%)、愈创木酚(0.47%)等 In the cooling stage of liquid hot water pretreatment, the amount of pseudo-lignin formation was 19.6 mg· g^-1 raw material. The induced pseudo-lignin contained lignin oligomer (71.46%), furan (9.44%), hydroxybenzoic acid (5.19%), HMF (1.18%), vanillin (1.42%), butanal (1.89%) and guaiacol (0.47%)	Zhuanget al.,(2017)
	杨木 Poplar wood	/	15.8	27.0	含有的木质素约为27%，木聚糖约为16% Contains about 27% lignin and 16% xylan	蒸汽爆破预处理过程中，假木质素形成模型为木聚糖解聚和醋酸中木质素溶解、浓缩2个一级反应动力学模型的结合，模型里还需要引入糠醛和木质素聚合2个旁路反应 In the process of steam explosion pretreatment, the formation model of pseudo-lignin is the combination of two first-order reaction kinetic models, namely, depolymerization of xylan and dissolution and concentration of lignin in acetic acid. Two bypass reactions, furfural and lignin polymerization, need to be introduced into the model	Sui et al., 2009
针叶材 Softwood	挪威云杉 Picea abies	42.7	18.6	27.9	阿拉伯糖(1.1%)、甘露糖(1.7%)、葡萄糖(42.7%)、木糖(4.3%)、半乳糖(11.6%)和木质素(27.9%)等 Arabinose (1.1%), mannose (1.7%), glucose (42.7%), xylose (4.3%), galactose (11.6%) and lignin (27.9%)	经预处理(260 ℃，8 min)后，假木质素含量增加至30.4% After pretreatment (260 ℃, 8 min), the content of pseudo-lignin increased to 30.4%	Normark et al., 2016
针叶材 Softwood	松木 Pine wood	39.88	18.63	32.06	阿拉伯糖(1.1%)、甘露糖(2.11%)、葡萄糖(39.88%)、木糖(5.71%)、半乳糖(9.71%)和木质素(32.06%)等 Arabinose (1.1%), mannose (2.11%), glucose (39.88%), xylose (5.71%), galactose (9.71%) and lignin (32.06%)	自水解预处理后酸不溶性木质素(假木质素)含量增加至46.11% The content of acid insoluble lignin (pseudo-lignin) increased to 46.11% after autohydrolysis pretreatment	Haoet al.,(2017)
禾本科植物 Gramineae	玉米皮 Maize stem rind	41.3(120 ℃预处理后) 41.3(after 120 ℃ pretr-eatment)	26.2(120 ℃预处理后) 26.2(after 120 ℃ pretr-eatment)	22.7(120 ℃预处理后) 22.7(after 120 ℃ pretr-eatment)	经120 ℃预处理后的原料中含葡萄糖(41.3%)、木聚糖(23.1%)、阿拉伯糖(3.1%)和克拉森木质素(22.7%) The raw materials pretreated at 120 ℃ contained glucose (41.3%), xylan (23.1%), arabinose (3.1%) and Klason lignin (22.7%)	高压热水预处理后形成游离和吸附假木质素微球，游离型假木质素微球产量为1.7 mg·g^-1(140 ℃)~13.8 mg·g^-1(180 ℃)，尺寸分布为：50 nm~0.8μm(140 ℃)，100~500 nm(160 ℃)，1 μm~100 nm(180 ℃)；对于吸附性微球，特征如下：均匀球形，约100 nm(120 ℃)，400 nm(140 ℃)，200~300 nm(160 ℃)，几纳米~1 μm(180 ℃) After high pressure hot water pretreatment, free and adsorbed pseudo-lignin microspheres were formed. The yield of free pseudo-lignin microspheres was about 1.7 mg·g^-1(140 ℃)-13.8 mg·g^-1(180 ℃), and the size distribution was 50 nm-0.8 μm(140 ℃)，100-500 nm(160 ℃)，1 μm-100 nm(180 ℃). For adsorbed microspheres, the characteristics were as follows: uniform sphere, about 100 nm (120 ℃), 400 nm (140 ℃) ℃), 200-300 nm (160 ℃), several nm ~ 1 μ m (180 ℃)	Yang et al., 2015
	小麦秸秆 Wheat straw	39.0	26.1	21.8	含葡萄糖(39.0%)、木聚糖(23.7%)、阿拉伯糖(1.6%)、半乳糖(0.8%)、乙酰基团(1.9%)、克拉森木质素(21.8%)、灰分(4.2%)等，木质素M_w为4 690 g·mol^-1 It contains glucose (39.0%), xylan (23.7%), arabinose (1.6%), galactose (0.8%), acetyl group (1.9%), Klason lignin (21.8%), ash (4.2%), etc. the M_w of lignin is 4 690 g·mol^-1	假木质素比木质素更容易溶解于液氨，形成的假木质素分子质量M_w分布范围为5 450~1 700 g·mol^-1 Compared with lignin, pseudo-lignin is more easily dissolved in liquid ammonia, and the M_w distribution of the formed pseudo-lignin is in the range of 5 450~1 700 g·mol^-1	Sipponen et al., 2014
竹子 Bamboo	综纤维素 Holocellulose	/	/	~1.0	170 ℃, H₂O, 30 min预处理，克拉森木质素含量1.5% 170 ℃, H₂O, 30 min pretreatment, Klason lignin content 1.5%	生成痕量假木质素 Generation of trace pseudo-lignin	Maet al.,(2015)
					170 ℃, H₂O, 90 min预处理，克拉森木质素含量2.0% 170 ℃, H₂O, 90 min pretreatment, Klason lignin content 2.0%	生成痕量假木质素 Generation of trace pseudo-lignin
					170 ℃, H₂O, 150 min预处理，克拉森木质素含量3.1% 170 ℃, H₂O, 150 min pretreatment, Klason lignin content 3.1%	假木质素得率为58.2%，M_w为3 410 g·mol^-1，M_n为1 200 g·mol^-1，PDI为2.84 The yield of pseudo-lignin is 58.2%, M_w 3 410 g·mol^-1，M_n 1 200 g·mol^-1，PDI 2.84
					170 ℃, H₂O, 240 min预处理，克拉森木质素含量6.2% 170 ℃, H₂O, 240 min pretreatment, Klason lignin content 6.2%	假木质素得率为54.1%，M_w为5 430 g·mol^-1，M_n为3 320 g·mol^-1，PDI为2.84 The yield of pseudo-lignin is 54.1%, M_w 5 430 g·mol^-1，M_n 3 320 g·mol^-1，PDI 2.84

Table 4

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Advances in Pseudo-Lignin Deposition and Its Effects on Enzymatic Hydrolysis of Cellulose

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