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1.
Bioresour Technol ; 299: 122685, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31918970

RESUMO

Different pretreatments strategies have been developed over the years mainly to enhance enzymatic cellulose degradation. In the new biorefinery era, a more holistic view on pretreatment is required to secure optimal use of the whole biomass. Hydrothermal pretreatment technology is regarded as very promising for lignocellulose biomass fractionation biorefinery and to be implemented at the industrial scale for biorefineries of second generation and circular bioeconomy, since it does not require no chemical inputs other than liquid water or steam and heat. This review focuses on the fundamentals of hydrothermal pretreatment, structure changes of biomass during this pretreatment, multiproduct strategies in terms of biorefinery, reactor technology and engineering aspects from batch to continuous operation. The treatise includes a case study of hydrothermal biomass pretreatment at pilot plant scale and integrated process design.


Assuntos
Lignina , Vapor , Biomassa , Celulose , Fracionamento Químico , Engenharia , Hidrólise
2.
Bioresour Technol ; 297: 122471, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31787511

RESUMO

Hereon, tobacco stalk was deconstructed by lyophilization, ball-milling, ultrasound-assisted alkali extraction, hydrothermal pretreatment (HTP), and alkali presoaking, respectively, followed by dilute alkali cooking to both improve its enzymatic digestibility and isolate the hemicellulosic streams. It was found that a maximum cellulose saccharification rate of 93.5% was achieved from the integrated substrate by ball-milling and dilute alkali cooking, which was 4.4-fold higher than that from the raw material. Interestingly, in this case, 76.9% of hemicelluloses were simultaneously recovered during the integrated treatment. Structural determination indicated that the hemicelluloses released from tobacco stalk by dilute alkali cooking were mixed polysaccharides, and the (1 â†’ 4)-linked ß-D-Xylp backbone branched with L-Araf units at O-2/O-3 and 4-O-Me-α-D-GlcpA units at O-2 of the xylose residues was the main structure. In comparison, ultrasound-assisted alkali extraction, ball-milling, and HTP favored the extraction of hemicelluloses with less branched structure and lower molecular weights in the following alkali cooking.


Assuntos
Celulose , Tabaco , Hidrólise , Peso Molecular , Polissacarídeos
3.
Bioresour Technol ; 243: 1105-1111, 2017 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-28764117

RESUMO

A biphasic pretreatment was adopted to disturb the recalcitrant structure of bamboo for further enzymatic hydrolysis and to obtain easily valorized lignin by-product. The biphasic system consisted of biomass-derived chemicals-2-methyltetrahydrofuran and oxalic acid as well as water, and the reactions were conducted at 120-180°C for 20min. The treatment resulted in notable removal of hemicelluloses and lignin. After the pretreatment, the cellulose conversion rate during enzymatic hydrolysis was enhanced by 6.7-fold as compared to the unpretreated raw material. Comprehensive analysis of the lignin product indicated that it exhibited representative structure (such as ß-O-4, ß-ß linkages) as compared to native lignin, contained a very low amount of contaminated sugars (0.67-2.39%), and had a relatively medium molecular weight (Mw 2240-3730g/mol) and good solubility in many organic solvents. This indicated that the lignin showed great potential application in conversion into materials and liquid fuels.


Assuntos
Furanos , Lignina , Ácido Oxálico , Celulose , Hidrólise , Água
4.
Bioresour Technol ; 222: 175-181, 2016 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-27718400

RESUMO

An integrated process based on ionic liquids ([Bmim]Cl and [Bmim]OAc) pretreatment and successive alkali post-treatments (0.5, 2.0, and 4.0% NaOH at 90°C for 2h) was performed to isolate lignins from Eucalyptus. The structural features and spatial distribution of lignin in the Eucalyptus cell wall were investigated thoroughly. Results revealed that the ionic liquids pretreatment promoted the isolation of alkaline lignin from the pretreated samples without obvious structural changes. Additionally, the integrated process resulted in syringyl-rich lignin macromolecules with more ß-O-4' linkages and less phenolic hydroxyl groups. Confocal Raman microscopy analysis showed that the dissolution behavior of lignin was varied in the morphologically distinct regions during the successive alkali treatments, and lignin dissolved was mainly stemmed from the secondary wall regions. These results provided some useful information for understanding the mechanisms of delignification during the integrated process and enhancing the potential utilizations of lignin in future biorefineries.


Assuntos
Parede Celular/química , Eucalyptus/química , Lignina/isolamento & purificação , Álcalis/análise , Líquidos Iônicos/química , Caules de Planta/química
5.
Biotechnol Biofuels ; 9: 166, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27499809

RESUMO

BACKGROUND: The biomass recalcitrance resulting from its chemical compositions and physical structures impedes the conversion of biomass into fermentable sugars. Pretreatment is a necessary procedure to increase the cellulase accessibility for bioconversion of lignocelluloses into bioethanol. Alternatively, ionic liquids, a series of promising solvents, provide unique opportunities for pretreating a wide range of lignocellulosic materials. In this study, a two-step treatment including ionic liquids pretreatment and successive alkali fractionations was performed on Eucalyptus to achieve a high enzymatic digestibility. The compositional and structural changes of Eucalyptus cell walls and their possible effect on saccharification ratio were comprehensively investigated. RESULTS: After the ionic liquids pretreatment, the cell walls became loose and even swelled, accompanying with the decrease of cellulose crystallinity. As compared to the simplex ionic liquids pretreatment, the integrated process resulted in the significant removal of hemicelluloses and lignin, enhancing the disruption of the cell walls and increasing the exposure of cellulose, which led to a higher conversion of cellulose to glucose. The glucose yield of Eucalyptus underwent the combination of [Bmim]OAc and alkali treatments reached the maximum (90.53 %), which was 6.6 times higher than that of the untreated Eucalyptus. The combination of chemical compositions and physical structure of Eucalyptus affected the efficiency of cellulose enzymatic hydrolysis. Especially, the changes of cellulose crystallinity played a major role in enhancing the enzymatic digestibility of Eucalyptus in this study. CONCLUSIONS: The two-step treatment with ionic liquids pretreatment and successive alkali fractionation can be considered as a promising method to improve the conversion of cellulose to glucose. The detailed information obtained about chemical and anatomical changes was helpful to understand the underlying mechanism of the integrated treatment process acting on Eucalyptus for enhancing enzymatic digestibility.

6.
Carbohydr Polym ; 123: 17-26, 2015 Jun 05.
Artigo em Inglês | MEDLINE | ID: mdl-25843830

RESUMO

Eucalyptus was sequentially extracted with 70% ethanol containing 0.4, 1.0, 2.0, 3.0, and 5.0% NaOH for 2h at 80°C. The chemical composition and structural features of the hemicellulosic fractions obtained were comparatively characterized by the combination of high-performance anion-exchange chromatography, gel permeation chromatography, Fourier transform infrared, and nuclear magnetic resonance spectroscopies. Furthermore, the main component distribution and their changes in cell wall were investigated by confocal Raman microscopy. Based on the Fourier transform infrared and nuclear magnetic resonance analyses, the hemicelluloses extracted from Eucalyptus mainly have a linear backbone of (1→4)-linked-ß-d-xylopyranosyl residues decorated with branch at O-2 of 4-O-methyl-α-glucuronic acid unit. Raman analysis revealed that the dissolution of hemicelluloses was different in the morphological regions, and the hemicelluloses released mainly originated from the secondary wall. The information obtained from the study conducted by combining chemical characterization with ultrastructure provides important basis for studying the mechanism of the alkali treatment.


Assuntos
Etanol/química , Eucalyptus/química , Polissacarídeos/química , Hidróxido de Sódio/química , Parede Celular/química , Espectroscopia de Ressonância Magnética , Peso Molecular , Solubilidade , Espectroscopia de Infravermelho com Transformada de Fourier , Análise Espectral Raman , Madeira/química
7.
Bioresour Technol ; 176: 296-9, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25435069

RESUMO

In this work, the structural features of the lignin isolated with 2% NaOH at 90°C for 2.5h from the hydrothermally pretreated eucalyptus fibers at different temperatures (100-200°C) for different times (15-60min) were thoroughly investigated. Results showed that the hydrothermal pretreatment facilitated the separation of alkali lignin from the pretreated fibers. It was found that the linkages of ß-O-4, ß-ß, and ß-5 decreased gradually with the increase of hydrothermal severity. Furthermore, decreased molecular weights (1630-510g/mol), associated carbohydrates contents (1.99-0.05%) and aliphatic OH contents (3.37-0.65mmol/g), and increased phenolic OH contents (0.71-2.98mmol/g) and thermal stability of the alkali lignins were observed with the increase of the hydrothermal severity.


Assuntos
Eucalyptus/química , Lignina/química , Temperatura , Álcalis/química , Fracionamento Químico , Cromatografia em Gel , Estrutura Molecular , Ressonância Magnética Nuclear Biomolecular , Espectroscopia de Infravermelho com Transformada de Fourier , Termogravimetria
8.
Bioresour Technol ; 175: 473-9, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25459857

RESUMO

In this study, sweet sorghum stem was subjected to hydrothermal pretreatment (HTP) and alkaline post-treatment to enhance its saccharification ratio by reducing its recalcitrance. The results showed that the HTP (110-210°C, 0.5-2.0h) significantly degraded hemicelluloses, and the pretreatment at the temperature higher than 190°C led to the partial degradation of the cellulose. As compared to the sole HTP, the integrated process removed most of lignin and hemicelluloses, which incurred a higher cellulose saccharification ratio. Under an optimum condition evaluated (HTP at 170°C for 0.5h and subsequent 2% NaOH treatment), 77.5% saccharification ratio was achieved, which was 1.8, 2.0 and 5.5 times as compared to the only HTP pretreated substrates, alkaline treated substrates alone and the raw material without pretreatment, respectively. Clearly, the integrated process can be considered as a promising approach to achieve an efficient conversion of lignocellulose to fermentable glucose.


Assuntos
Antiácidos/farmacologia , Metabolismo dos Carboidratos , Celulase/metabolismo , Caules de Planta/metabolismo , Sorghum/metabolismo , Temperatura , Reatores Biológicos , Metabolismo dos Carboidratos/efeitos dos fármacos , Celulose/metabolismo , Fermentação/efeitos dos fármacos , Glucose/metabolismo , Hidrólise/efeitos dos fármacos , Lignina/metabolismo , Polissacarídeos/metabolismo , Água/farmacologia
9.
J Agric Food Chem ; 62(25): 5939-47, 2014 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-24927101

RESUMO

An environmentally friendly steam explosion process of bamboo, followed by alkali and alkaline ethanol delignification, was developed to fractionate lignins. Results showed that after steam explosion the lignins isolated showed relatively low carbohydrate contents (0.55-1.76%) and molecular weights (780-1050 g/mol). For each steam-exploded sample, alkali-extracted lignins presented higher phenolic OH values (1.41-1.82 mmol/g), p-coumaric acid to ferulic acid ratios (pCA/FA ratios 4.5-14.1), and syringyl to guaiacyl ratios (S/G ratios 5.0-8.5) than those from alkaline ethanol-extracted lignins (phenolic OH 0.85-1.35 mmol/g, pCA/FA ratios 1.6-5.2, and S/G ratios 3.5-4.8). The lignins obtained consisted mainly of ß-O-4' linkages combined with small amounts of ß-ß', ß-5', and α-O-4/ß-O-4 linkages. Antioxidant activities of the lignins obtained were tested by the 2,2-diphenyl-1-picrylhydrazyl, 2,2'-azobis(3-ethylbenzothiazoline-6-sulfonic acid), and ferric reducing activity power methods. It was found that alkali-extracted lignins obtained during the initial extraction process had higher antioxidant activities than alkaline ethanol-extracted lignins obtained during the second extraction process.


Assuntos
Antioxidantes/química , Lignina/química , Extratos Vegetais/química , Poaceae/química , Antioxidantes/isolamento & purificação , Biotecnologia , Lignina/isolamento & purificação , Estrutura Molecular , Peso Molecular , Extratos Vegetais/isolamento & purificação , Espectroscopia de Infravermelho com Transformada de Fourier , Vapor
10.
Bioresour Technol ; 163: 377-80, 2014 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-24830378

RESUMO

In this study, cellulose-rich fractions from bamboo were prepared with steam explosion pretreatment (SEP) followed by a successive alkaline delignification to improve the enzymatic digestibility for an efficient bioethanol production. The cellulose-rich fractions obtained were characterized by FT-IR, XRD, CP/MAS (13)C NMR, SEM, and BET surface area. It was found that the SEP alone significantly removed partial hemicelluloses, while the synergistic treatment by SEP and alkaline delignification removed most hemicelluloses and lignin. Results from enzymatic hydrolysis showed that SEP alone improved the enzymatic hydrolysis rate by 7.9-33.1%, while the synergistic treatment by SEP and alkaline delignification enhanced the rate by 45.7-63.9%. The synergistic treatment by SEP at 2.0 MPa for 5 min with water impregnation followed by a successive alkaline delignification with 0.5% NaOH and 70% ethanol containing 1.5% NaOH resulted in a maximum enzymatic hydrolysis rate of 70.6%.


Assuntos
Álcalis/metabolismo , Bambusa/metabolismo , Celulase/metabolismo , Celulose/metabolismo , beta-Glucosidase/metabolismo , Hidrólise
11.
Int J Biol Macromol ; 69: 158-64, 2014 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-24867208

RESUMO

In this study, an environmental-friendly hydrothermal pretreatment of Eucalyptus fiber followed with alkali post-treatment was developed to produce bioethanol efficiently. This biorefinery process allowed all major components of biomass being converted into high value-added products. The chemical and structural features of the residual hemicelluloses isolated with alkali from the hydrothermal pretreated Eucalyptus fiber, were comparatively investigated. Sugar and spectral analyses indicated that the hemicelluloses were mainly composed of glucuronoxylans, and especially hemicelluloses prepared at higher temperature (180°C) contained higher contents of glucomannans and α-glucan. Hydrothermal pretreatment resulted in a significant hydrolysis of the glycosidic linkages in xylan backbone, and thus the molecular weight of the hemicelluloses was significantly reduced from 56,520 to 7780g/mol with the increase of temperature. This suggested that a combination of hydrothermal pretreatment at low temperatures (100-140°C) and alkali post-treatment was an effective technique for isolating of hemicelluloses from Eucalyptus fiber.


Assuntos
Eucalyptus/química , Polissacarídeos/química , Temperatura , Água/química , Fenômenos Químicos , Química Verde , Peso Molecular , Oligossacarídeos/química
12.
Carbohydr Polym ; 101: 1191-7, 2014 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-24299891

RESUMO

An environmentally friendly pretreatment process was developed to fractionate hemicelluloses from dried and water-immersed Phyllostachys pubescens chips by steam explosion followed with alkali and alkali/ethanol extractions. The detailed chemical and structural features of the isolated hemicellulosic fractions were comparatively investigated by HPAEC, GPC, FT-IR, (13)C NMR spectroscopies, and TGA analysis. It was found that the xylose/arabinose ratios of hemicelluloses obtained from alkali and alkali/ethanol extractions were 21.5-34.4 and 7.7-9.9, respectively, suggesting that hemicelluloses extracted with alkali had relatively lower degree of branches than those extracted with alkali/ethanol. Hemicellulosic fractions isolated from the water-immersed samples were obtained in high yields and exhibited similar compositions, which can be used as raw materials for production of value-added products. Furthermore, the hemicelluloses extracted with alkali had relatively higher molecular weight than those extracted with alkali/ethanol. In addition, an increment of incubation time resulted in a decreased thermal stability of hemicelluloses obtained from water-immersed sample.


Assuntos
Poaceae/química , Polissacarídeos/química , Vapor , Concentração de Íons de Hidrogênio , Peso Molecular , Temperatura , Ácidos Urônicos/análise
13.
Bioresour Technol ; 150: 278-86, 2013 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-24184648

RESUMO

Bamboo (Phyllostachys pubescens) was successfully fractionated using a three-step integrated process: (1) autohydrolysis pretreatment facilitating xylooligosaccharide (XOS) production (2) organosolv delignification with organic acids to obtain high-purity lignin, and (3) extended delignification with alkaline hydrogen peroxide (AHP) to produce purified pulp. The integrated process was comprehensively evaluated by component analysis, SEM, XRD, and CP-MAS NMR techniques. Emphatically, the fundamental chemistry of the lignin fragments obtained from the integrated process was thoroughly investigated by gel permeation chromatography and solution-state NMR techniques (quantitative (13)C, 2D-HSQC, and (31)P-NMR spectroscopies). It is believed that the integrated process facilitate the production of XOS, high-purity lignin, and purified pulp. Moreover, the enhanced understanding of structural features and chemical reactivity of lignin polymers will maximize their utilizations in a future biorefinery industry.


Assuntos
Bambusa/química , Fracionamento Químico/métodos , Lignina/química , Lignina/isolamento & purificação , Compostos Orgânicos/farmacologia , Caules de Planta/química , Solventes/farmacologia , Bambusa/efeitos dos fármacos , Hidrólise , Espectroscopia de Ressonância Magnética , Peso Molecular , Caules de Planta/efeitos dos fármacos , Difração de Raios X
14.
J Agric Food Chem ; 60(44): 11120-7, 2012 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-23057617

RESUMO

Pretreatment is the key to unlock the recalcitrance of lignocellulosic biomass for the productions of biofuels. Ionic liquid pretreatment has drawn increased attention because of its numerous advantages over conventional methods. In this study, corncob was submitted to pretreatments with 1-ethyl-3-methylimadazolium acetate (EMIMAc) and/or H(2)O/dimethyl sulfoxide (DMSO) followed by alkaline extraction to isolate hemicelluloses. The hemicellulosic fractions obtained were comprehensively characterized with a series of chemical and spectroscopic technologies, including gel permeation chromatography (GPC), thermogravimetric analysis (TGA), high-performance anion-exchange chromatography (HPAEC), Fourier transform infrared (FTIR) spectroscopy, and one- and two-dimensional nuclear magnetic resonance (NMR). The results showed that the fractions prepared with ionic liquid pretreatments exhibited relatively higher average molecular weights (196,230-349,480 g/mol) than the fraction prepared without pretreatment (M(w), 96,260 g/mol). Furthermore, the pretreated fractions demonstrated higher thermal stability compared to the fractions without pretreatment. Structural characterization indicated that all of the fractions had similar structures, which are composed of a (1 → 4)-linked ß-D-xylopyranosyl backbone substituted with arabinofuranosyls attached to O-2 and O-3 and with 4-O-methyl-α-D-glucuronic acid also linked to O-2.


Assuntos
Líquidos Iônicos/química , Polissacarídeos/química , Zea mays/química , Configuração de Carboidratos , Cromatografia em Gel , Cromatografia Líquida de Alta Pressão , Cromatografia por Troca Iônica , Espectroscopia de Ressonância Magnética , Peso Molecular , Espectroscopia de Infravermelho com Transformada de Fourier , Termogravimetria
15.
J Agric Food Chem ; 60(7): 1703-12, 2012 Feb 22.
Artigo em Inglês | MEDLINE | ID: mdl-22283627

RESUMO

Fractionation of lignocellulosic material into its constitutive components is of vital importance for the production of biofuels as well as other value-added chemicals. The conventional acetosolv processes are mainly focused on the production of pulp from woody lignocelluloses. In this study, a mild acetosolv process was developed to fractionate bamboo under atmospheric pressure to obtain cellulosic pulp, water-soluble fraction, and acetic acid lignin. The structural features of the lignins obtained under various conditions were characterized with elemental analysis, sugar analysis, alkaline nitrobenzene oxidation, gel permeation chromatography (GPC), (1)H nuclear magnetic resonance ((1)H NMR), and heteronuclear single-quantum coherence (HSQC) spectroscopy. As compared to milled wood lignin (MWL) of bamboo, acetic acid lignins had low impurities (carbohydrates 2.48-4.56%) mainly due to the cleavage of linkages between lignin and carbohydrates. In addition, acetic acid lignins showed a low proportion of syringyl (S) units. Due to the cleavage of linkages between lignin units, acetic acid lignins had weight-average molecular weights ranging from 4870 to 5210 g/mol, less than half that of MWL (13000 g/mol). In addition, acetic acid lignins showed stronger antioxidant activity mainly due to the significant increase of free phenolic hydroxyls. The lignins obtained with such low impurities, high free phenolic hydroxyls, and medium molecular weights are promising feedstocks to replace petroleum chemicals.


Assuntos
Ácido Acético , Antioxidantes/farmacologia , Lignina/química , Lignina/farmacologia , Poaceae/química , Fracionamento Químico , Lignina/análise , Espectroscopia de Ressonância Magnética , Estrutura Molecular , Peso Molecular , Soluções
16.
Ultrason Sonochem ; 19(2): 243-9, 2012 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-21784690

RESUMO

Bamboo was submitted to ultrasound-assisted extraction in aqueous ethanol to evaluate the effect of ultrasonic irradiation on the dissolution of lignin. In this case, the dewaxed bamboo culms were subjected to ball milling for 48 h, and then were suspended in 95% ethanol followed by ultrasonic irradiations for varied times at 20 °C to obtain ethanol-soluble fractions. The structural and thermal properties of the ethanol-soluble fractions were comparatively investigated by chemical analysis including alkaline nitrobenzene oxidation, bound carbohydrate determination, FT-IR spectra, HSQC spectra, TG, and DTA. The results showed that the yields of the ethanol-soluble fractions were between 4.29% and 4.76% for the fractions prepared with ultrasonic irradiation time ranging from 5 to 55 min, as compared to 4.02% for the fraction prepared without ultrasonic irradiation. It was found that the lignin content of the fraction increased with the increase of the ultrasonic irradiation time. There was a slight increase of the molecular weight of the lignin with the increase of the ultrasonic irradiation time. Alkaline nitrobenzene oxidation coupled with HSQC analysis indicated that the lignin in the fractions was mainly composed of GSH type units as well as minor amounts of ferulic acids. In addition, the fraction prepared with ultrasonic irradiation exhibited a slightly higher thermal stability as compared to the fraction prepared without ultrasonic irradiation.


Assuntos
Fracionamento Químico/métodos , Etanol/química , Lignina/química , Lignina/isolamento & purificação , Poaceae/química , Ultrassom , Solubilidade , Espectroscopia de Infravermelho com Transformada de Fourier , Temperatura , Fatores de Tempo
17.
Food Chem ; 134(3): 1392-8, 2012 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-25005958

RESUMO

Microwave-assisted extraction in organic acid aqueous solution (formic acid/acetic acid/water, 3/5/2, v/v/v) was applied to isolate lignin from bamboo. Additionally, the structural features of the extracted lignins were thoroughly investigated in terms of C9 formula, molecular weight distribution, FT-IR, (1)H NMR and HSQC spectroscopy. It was found that with an increase in the severity of microwave-assisted extraction, there was an increase of phenolic hydroxyl content in the lignin. In addition, an increase of the severity resulted in a decrease of the bound carbohydrate content as well as molecular weight of the lignin. Antioxidant activity investigation indicated that the radical scavenging index of the extracted lignins (0.35-1.15) was higher than that of BHT (0.29) but lower than that of BHA (3.85). The results suggested that microwave-assisted organic acid extraction provides a promising way to prepare lignin from bamboo with good antioxidant activity for potential application in the food industry.


Assuntos
Antioxidantes/química , Antioxidantes/farmacologia , Lignina/química , Lignina/farmacologia , Micro-Ondas , Poaceae/química , Ácido Acético/química , Antioxidantes/isolamento & purificação , Fracionamento Químico/métodos , Formiatos/química , Lignina/isolamento & purificação , Espectroscopia de Ressonância Magnética , Estrutura Molecular , Oxirredução , Extratos Vegetais/química , Extratos Vegetais/isolamento & purificação , Extratos Vegetais/farmacologia , Espectroscopia de Infravermelho com Transformada de Fourier
18.
J Agric Food Chem ; 59(19): 10604-14, 2011 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-21879769

RESUMO

To characterize the lignin structures and lignin-carbohydrate complex (LCC) linkages, milled wood lignin (MWL) and mild acidolysis lignin (MAL) with a high content of associated carbohydrates were sequentially isolated from ball-milled poplar wood. Quantification of their structural features has been achieved by using a combination of quantitative (13)C and 2D HSQC NMR techniques. The results showed that acetylated 4-O-methylgluconoxylan is the main carbohydrate associated with lignins, and acetyl groups frequently acylate the C2 and C3 positions. MWL and MAL exhibited similar structural features. The main substructures were ß-O-4' aryl ether, resinol, and phenylcoumaran, and their abundances per 100 Ar units changed from 41.5 to 43.3, from 14.6 to 12.7, and from 3.7 to 4.0, respectively. The S/G ratios were estimated to be 1.57 and 1.62 for MWL and MAL, respectively. Phenyl glycoside and benzyl ether LCC linkages were clearly quantified, whereas the amount of γ-ester LCC linkages was ambiguous for quantification.


Assuntos
Carboidratos/química , Lignina/química , Acilação , Configuração de Carboidratos , Espectroscopia de Ressonância Magnética , Estrutura Molecular , Peso Molecular , Madeira/química
19.
J Agric Food Chem ; 59(12): 6605-15, 2011 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-21568341

RESUMO

To improve yields while minimizing the extent of mechanical action (just 2 h of planetary ball-milling), the residual wood meal obtained from extraction of milled wood lignin (MWL) was sequentially treated with cellulolytic enzyme and alkali, and the yields of MWL, cellulolytic enzyme lignin (CEL), and alkaline lignin (AL) were 5.4, 23.2, and 16.3%, respectively. The chemical structures of the lignin fractions obtained were characterized by carbohydrate analysis, gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectroscopy, and various advanced NMR spectroscopic techniques. The results showed that the lignin isolated as MWL during the early part of ball milling may originate mainly from the middle lamella. This lignin fraction was less degradable and contained more linear hemicelluloses and more C═O in unconjugated groups as well as more phenolic OH groups. Both 1D and 2D NMR spectra analyses confirmed that the lignin in triploid of Populus tomentosa Carr. is GSH-type and partially acylated at the γ-carbon of the side chain. Two-dimensional heteronuclear single-quantum coherence (¹³C-¹H) NMR of MWL, CEL, and AL showed a predominance of ß-O-4' aryl ether linkages (81.1-84.5% of total side chains), followed by ß-ß' resinol-type linkages (12.2-16.4%), and lower amounts of ß-5' phenylcoumaran (2.1-2.6%) and ß-1' spirodienone-type (0.4-1.4%) linkages. The syringyl (S)/guaiacyl (G) ratios were estimated to be 1.43, 2.29, and 2.83 for MWL, CEL, and AL, respectively.


Assuntos
Lignina/química , Populus/química , Triploidia , Espectroscopia de Ressonância Magnética , Estrutura Molecular , Populus/genética , Espectroscopia de Infravermelho com Transformada de Fourier
20.
Carbohydr Res ; 346(1): 111-20, 2011 Jan 03.
Artigo em Inglês | MEDLINE | ID: mdl-21109235

RESUMO

The physicochemical properties and structural characteristics of seven alkali-soluble hemicellulosic preparations were determined. These were extracted from bamboo (Bambusa rigida) with 1M NaOH, KOH, LiOH, NH(3)·H(2)O, (CH(3)CH(2))(3)N, Ca(OH)(2), Ba(OH)(2), respectively, at 50°C for 3h, were comparatively studied. Sugar analysis showed that these hemicelluloses contained d-xylose as the major constituent, along with d-glucose and l-arabinose in noticeable amounts. Uronic acids, principally 4-O-methyl-d-glucuronic acid, occurred in a small amount. Furthermore, based on the sugar analysis and FTIR and NMR spectroscopy, it can be concluded that the hemicelluloses consist of a backbone of ß-(1→4)-linked d-xylopyranosyl units having branches of arabinose and 4-O-methyl-d-glucuronic acid. Nitrobenzene oxidation revealed that the hemicelluloses obtained are mostly free of bound lignins. Moreover, it is noteworthy that hemicelluloses isolated with the different alkaline solutions presented different chemical compositions and slightly dissimilar structural features, indicating that alkalinity played an important role in cleaving the chemical linkages between the hemicelluloses and the lignins.


Assuntos
Álcalis/química , Bambusa/química , Polissacarídeos/química , Espectroscopia de Ressonância Magnética , Polissacarídeos/isolamento & purificação , Solubilidade , Espectroscopia de Infravermelho com Transformada de Fourier
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