RESUMEN
Papyri belong to the oldest writing grounds in history. Their conservation is of the highest importance in preserving our cultural heritage, which is best achieved based on an extensive knowledge of the materials' constituents to choose a tailored conservation approach. Thermogravimetric Analysis (TGA) has been widely employed to quantify cellulose and lignin in papyrus sheets, yielding reported lignin contents of 25% to 40%. In this work, the TGA method conventionally used for papyrus samples was repeated and compared to other lignin determination approaches (Klason-lignin and acetyl bromide-soluble lignin). TGA can lead to a large overestimation of the lignin content of commercial papyrus sheets (~27%) compared to the other methods (~5%). A similar overestimation of the lignin content was found for the pith and rind of the native papyrus plant. We concluded that the TGA method should, therefore, not be used for lignin quantification.
Asunto(s)
Lignina/análisis , Extractos VegetalesRESUMEN
Lignins from different tree barks, including Norway spruce (Picea abies), eucalyptus (Eucalyptus globulus), mimosa (Acacia dealbata) and blackwood acacia (A. melanoxylon), are thoroughly characterized. The lignin from E.â globulus bark is found to be enriched in syringyl (S) units, with lower amounts of guaiacyl (G) and p-hydroxyphenyl (H) units (H/G/S ratio of 1:26:73), which produces a lignin that is highly enriched in ß-ether linkages (83 %), whereas those from the two Acacia barks have similar compositions (H/G/S ratio of ≈5:50:45), with a predominance of ß-ethers (73-75 %) and lower amounts of condensed carbon-carbon linkages; the lignin from A.â dealbata bark also includes some resorcinol-related compounds, that appear to be incorporated or intimately associated to the polymer. The lignin from P.â abies bark is enriched in G units, with lower amounts of H units (H/G ratio of 14:86); this lignin is thus depleted in ß-O-4' alkyl-aryl ether linkages (44 %) and enriched in condensed linkages. Interestingly, this lignin contains large amounts of hydroxystilbene glucosides that seem to be integrally incorporated into the lignin structure. This study indicates that lignins from tree barks can be seen as an interesting source of valuable phenolic compounds. Moreover, this study is useful for tailoring conversion technologies for bark deconstruction and valorization.
Asunto(s)
Lignina/química , Corteza de la Planta/química , Extractos Vegetales/química , Éteres/química , Eucalyptus/química , Cromatografía de Gases y Espectrometría de Masas , Glucósidos/química , Estructura Molecular , Fenol/química , Picea/química , Solventes/química , Estilbestroles/químicaRESUMEN
The structure of the lignin from brewer's spent grain (BSG) has been studied in detail. Three different lignin preparations, the so-called "milled-wood" lignin (MWL), dioxane lignin (DL), and cellulolytic lignin (CEL), were isolated from BSG and then thoroughly characterized by pyrolysis GC/MS, 2D-NMR, and derivatization followed by reductive cleavage (DFRC). The data indicated that BSG lignin presents a predominance of guaiacyl units (syringyl/guaiacyl ratio of 0.4-0.5) with significant amounts of associated p-coumarates and ferulates. The flavone tricin was also present in the lignin from BSG, as also occurred in other grasses. 2D-NMR (HSQC) revealed that the main substructures present are ß-O-4' alkyl-aryl ethers (77-79%) followed by ß-5' phenylcoumarans (11-13%) and lower amounts of ß-ß' resinols (5-6%) and 5-5' dibenzodioxocins (3-5%). The results from 2D-NMR (HMBC) and DFRC indicated that p-coumarates are acylating the γ-carbon of lignin side chains and are mostly involved in condensed structures. DFRC analyses also indicated a minor degree of γ-acylation with acetate groups, which takes place preferentially on S lignin (6% of S units are acetylated) over G lignin (only 1% of G units are acetylated).
Asunto(s)
Grano Comestible/química , Lignina/química , Lignina/aislamiento & purificación , Extractos Vegetales/química , Extractos Vegetales/aislamiento & purificación , Residuos/análisis , Madera/química , Acilación , Biocatálisis , Celulasa/química , Dioxanos/química , Dioxanos/aislamiento & purificación , Cromatografía de Gases y Espectrometría de Masas , Espectroscopía de Resonancia Magnética , Estructura MolecularRESUMEN
The effects and mechanism of pulp delignification by laccases in the presence of redox mediators have been investigated on unbleached eucalyptus kraft pulp treated with laccases from Pycnoporus cinnabarinus (PcL) and Myceliophthora thermophila (MtL) and 1-hydroxybenzotriazole (HBT) and methyl syringate (MeS) as mediators, respectively. Determination of the corrected κ number in eucalyptus pulps after the enzymatic treatments revealed that the PcL-HBT system exhibited a more remarkable delignification effect than the MtL-MeS system. To obtain further insight, lignin-carbohydrate complexes were fractionated and subsequently characterized by nuclear magnetic resonance, thioacidolysis (followed by gas chromatography and size exclusion chromatography), and pyrolysis-gas chromatography-mass spectrometry (pyrolysis-GC-MS) analyses before and after the enzymatic treatments and their controls. We can conclude that the laccase-mediator treatments altered the lignin structures in such a way that more lignin was recovered in the xylan-lignin fractions, as shown by Klason lignin estimation, with smaller amounts of both syringyl (S) and guaiacyl (G) uncondensed units, as shown by thioacidolysis and gas chromatography, especially after the PcL-HBT treatment. The laccase-mediator treatment produced oxidation at Cα and cleavage of Cα and Cß bonds in pulp lignin, as shown by pyrolysis-GC-MS. The general mechanism of residual lignin degradation in the pulp by laccase-mediator treatments is discussed in light of the results obtained.
Asunto(s)
Lacasa/química , Lignina/química , Xilanos/química , Ascomicetos/enzimología , Biocatálisis , Conformación de Carbohidratos , Eucalyptus/química , Proteínas Fúngicas/química , Lignina/aislamiento & purificación , Preparaciones de Plantas/química , Pycnoporus/enzimología , Xilanos/aislamiento & purificaciónRESUMEN
The chemical composition of the lipids in wheat straw was studied in detail by gas chromatography and mass spectrometry. Important discrepancies with the data reported in previous papers were found. The predominant lipids identified were series of long-chain free fatty acids (25% of total extract), followed by series of free fatty alcohols (ca. 20%). High molecular weight esters of long chain fatty acids esterified to long chain fatty alcohols were also found (11%), together with lower amounts of other aliphatic series, such as n-alkanes, n-aldehydes, and glycerides (mono-, di-, and triglycerides). Relatively high amounts of ß-diketones (10%), particularly 14,16-hentriacontanedione, which is the second most abundant single compound among the lipids in wheat straw, were also identified. Finally, steroid compounds (steroid hydrocarbons, steroid ketones, free sterols, sterol esters, and sterol glycosides) were also found, with sterols accounting for nearly 14% of all identified compounds.
Asunto(s)
Lípidos/química , Extractos Vegetales/química , Tallos de la Planta/química , Triticum/química , Ácidos Grasos/química , Cromatografía de Gases y Espectrometría de MasasRESUMEN
The structure of the isolated milled "wood" lignin from coconut coir has been characterized using different analytical methods, including Py-GC/MS, 2D NMR, DFRC, and thioacidolysis. The analyses demonstrated that it is a p-hydroxyphenyl-guaiacyl-syringyl (H-G-S) lignin, with a predominance of G units (S/G ratio 0.23) and considerable amounts of associated p-hydroxybenzoates. Two-dimensional NMR indicated that the main substructures present in this lignin include ß-O-4' alkyl aryl ethers followed by phenylcoumarans and resinols. Two-dimensional NMR spectra also indicated that coir lignin is partially acylated at the γ-carbon of the side chain with p-hydroxybenzoates and acetates. DFRC analysis showed that acetates preferentially acylate the γ-OH in S rather than in G units. Despite coir lignin's being highly enriched in G-units, thioacidolysis indicated that ß-ß' resinol structures are mostly derived from sinapyl alcohol. Finally, we find evidence that the flavone tricin is incorporated into the coconut coir lignin, as has been recently noted for various grasses.
Asunto(s)
Cocos/química , Lignina/análogos & derivados , Extractos Vegetales/química , Lignina/química , Lignina/aislamiento & purificación , Espectroscopía de Resonancia Magnética , Estructura Molecular , Extractos Vegetales/aislamiento & purificaciónRESUMEN
The composition of lipophilic extractives in the cortex and pith of elephant grass ( Pennisetum purpureum Schumach.) stems was thoroughly studied by gas chromatography-mass spectrometry. The predominant compounds were fatty acids followed by sterols (in free and conjugated forms as esters and glycosides). Other steroid compounds, as steroid hydrocarbons and ketones, were also present. Additionally, important amounts of mono-, di-, and triglycerides were identified. Other aliphatic series such as n-alkanes, n-fatty alcohols, and n-alkyl ferulates, together with tocopherols and a series of high molecular weight esters, were also found, although in minor amounts. The analyses also revealed the presence of a ß-diketone (12,14-tritriacontanedione), which was particularly abundant in the cortex. Finally, two lignans, matairesinol and syringaresinol, were also detected. In general terms, the abundances of the different classes of compounds were higher in the pith, except for the series of n-fatty alcohols, n-alkyl ferulates, ß-diketones, and lignans, which were more prominent in the cortex.
Asunto(s)
Pennisetum/química , Extractos Vegetales/análisis , Tallos de la Planta/química , Alcanos/análisis , Alcanos/aislamiento & purificación , Ácidos Grasos/análisis , Ácidos Grasos/aislamiento & purificación , Cromatografía de Gases y Espectrometría de Masas , Extractos Vegetales/aislamiento & purificación , Esteroles/análisis , Esteroles/aislamiento & purificaciónRESUMEN
The ability of Trametes villosa laccase, in conjuction with 1-hydroxybenzotriazole (HBT) as mediator and alkaline extraction, to remove lignin was demonstrated during treatment of wood (Eucalyptus globulus) and non-wood (Pennisetum purpureum) feedstocks. At 50 Ug(-1) laccase and 2.5% HBT concentration, 48% and 32% of the Eucalyptus and Pennisetum lignin were removed, respectively. Two-dimensional nuclear magnetic resonance of the feedstocks, swollen in dimethylsulfoxide-d(6), revealed the removal of p-hydroxyphenyl, guaiacyl and syringyl lignin units and aliphatic (mainly ß-O-4'-linked) side-chains of lignin, and a moderate removal of p-coumaric acid (present in Pennisetum) without a substantial change in polysaccharide cross-signals. The enzymatic pretreatment (at 25 Ug(-1)) of Eucalyptus and Pennisetum feedstocks increased the glucose (by 61% and 12% in 72 h) and ethanol (by 4 and 2 g L(-1) in 17 h) yields from both lignocellulosic materials, respectively, as compared to those without enzyme treatment.
Asunto(s)
Eucalyptus/química , Lacasa/química , Lignina/aislamiento & purificación , Pennisetum/química , Extractos Vegetales/química , Madera/química , HidrólisisRESUMEN
The ability of two natural phenols to act as mediators of the recombinant Myceliophthora thermophila laccase (MtL) in eucalypt-pulp delignification was investigated. After alkaline peroxide extraction, the properties of the enzymatically-treated pulps improved with respect to the control. The pulp brightness increased (3.1 points) after the enzymatic treatment with MtL alone, but the highest improvements were obtained after the MtL treatment using syringaldehyde (4.7 points) and especially methyl syringate (8.3 points) as mediators. Likewise, a decrease in kappa number up to 2.7 points was obtained after the MtL-methyl syringate treatment, followed by decreases of 1.4 and 0.9 points after the treatments with MtL-syringaldehyde and MtL alone, respectively. On the other hand, removal of the main lipophilic extractives present in eucalypt pulp was observed after the above laccase-mediator treatments. Finally, the doses of both MtL and methyl syringate were reduced, and results compatible with industrial implementation were obtained.
Asunto(s)
Reactores Biológicos , Lacasa/metabolismo , Lignina/metabolismo , Papel , Sordariales/enzimología , Eliminación de Residuos Líquidos/métodos , Benzaldehídos/metabolismo , Eucalyptus/química , Ácido Gálico/análogos & derivados , Ácido Gálico/metabolismo , Cromatografía de Gases y Espectrometría de Masas , Lignina/análisis , PolisorbatosRESUMEN
The fate of lipophilic extractives from several nonwoody species (flax, hemp, sisal and abaca) used for the manufacturing of cellulose pulps, was studied during soda/anthraquinone (AQ) pulping and totally chorine free (TCF) and elemental chlorine free (ECF) bleaching. With this purpose, the lipophilic extracts from the raw materials and their unbleached and bleached industrial pulps, were analyzed by gas chromatography-mass spectrometry. Aldehydes, hydroxyfatty acids and esterified compounds such as ester waxes, sterol esters and alkylferulates strongly decreased after soda/AQ pulping while alkanes, alcohols, free sterols and sterol glycosides survived the cooking process. Among the lipophilic extractives that remained in the unbleached pulps, some amounts of free sterols were still present in the TCF pulps whereas they were practically absent in the ECF pulps. Sterol glycosides were also removed after both TCF and ECF bleaching. By contrast, saturated fatty acids, fatty alcohols and alkanes were still present in both bleached pulps.
Asunto(s)
Álcalis/química , Antraquinonas/química , Compuestos de Calcio/química , Lignina/química , Lignina/aislamiento & purificación , Óxidos/química , Extractos Vegetales/química , Extractos Vegetales/aislamiento & purificación , Hidróxido de Sodio/química , Fraccionamiento Químico/métodos , Cloro/química , MaderaRESUMEN
The structure of lignins isolated from the herbaceous plants sisal ( Agave sisalana), kenaf ( Hibiscus cannabinus), abaca ( Musa textilis) and curaua ( Ananas erectifolius) has been studied upon spectroscopic (2D-NMR) and chemical degradative (derivatization followed by reductive cleavage) methods. The analyses demonstrate that the structure of the lignins from these plants is highly remarkable, being extensively acylated at the gamma-carbon of the lignin side chain (up to 80% acylation) with acetate and/or p-coumarate groups and preferentially over syringyl units. Whereas the lignins from sisal and kenaf are gamma-acylated exclusively with acetate groups, the lignins from abaca and curaua are esterified with acetate and p-coumarate groups. The structures of all these highly acylated lignins are characterized by a very high syringyl/guaiacyl ratio, a large predominance of beta- O-4' linkages (up to 94% of all linkages), and a strikingly low proportion of traditional beta-beta' linkages, which indeed are completely absent in the lignins from abaca and curaua. The occurrence of beta-beta' homocoupling and cross-coupling products of sinapyl acetate in the lignins from sisal and kenaf indicates that sinapyl alcohol is acetylated at the monomer stage and that, therefore, sinapyl acetate should be considered as a real monolignol involved in the lignification reactions.
Asunto(s)
Lignina/química , Magnoliopsida/química , Plantas Medicinales/química , Acetilación , Espectroscopía de Resonancia MagnéticaRESUMEN
In this paper, we show for the first time that lignin-derived phenols can act as laccase mediators for the removal of lipophilic compounds from paper pulp. These natural mediators represent an alternative to synthetic mediators, such as 1-hydroxybenzotriazole (HBT), that cause some economic and environmental concerns. Unbleached kraft pulp from eucalypt wood, which contained free and conjugated sterols responsible for pitch deposition in the manufacture of totally chlorine free paper, was treated with a fungal laccase in the presence of syringaldehyde, acetosyringone, and p-coumaric acid as mediators. The composition of lipophilic extractives in the pulps after the enzymatic treatment followed by a hydrogen peroxide stage was analyzed by gas chromatography and gas chromatography/mass spectrometry. The enzymatic treatment using syringaldehyde as laccase mediator caused the highest removal (over 90%) of free and conjugated sitosterol, similar to that attained with HBT, followed by acetosyringone (over 60% removal), whereas p-coumaric acid was barely effective. Moreover, recalcitrant oxidized steroids surviving laccase-HBT treatment could be removed when using these natural mediators. Pulp brightness was also improved (from 57% to 66% ISO brightness) by the laccase treatment in the presence of the above phenols followed by the peroxide stage due to the simultaneous removal of lignin.
Asunto(s)
Residuos Industriales , Lacasa/química , Lignina/química , Papel , Fenoles/química , Administración de Residuos/métodos , Acetofenonas/química , Benzaldehídos/química , Ácidos Cumáricos/química , Eucalyptus/química , Extractos Vegetales/química , Extractos Vegetales/aislamiento & purificación , Propionatos , Madera/químicaRESUMEN
A series of phenylphenalenone type compounds, known to play a role as phytoalexins in plants of the Musaceae family, have been identified for the first time in the leaf fibers of abaca (Musa textilis). Among the phenylphenalenone type compounds identified, the structure of a novel compound, (1R)-2,3-dihydro-4,9-dihydroxy-8-methoxy-1-phenylphenalene, has also been described in abaca fibers. Its structure was elucidated by analysis of one- and two-dimensional NMR (correlation spectroscopy, heteronuclear single quantum correlation, and heteronuclear multiple bond correlation) spectroscopic data.
Asunto(s)
Musa/química , Fenalenos/aislamiento & purificación , Cromatografía de Gases y Espectrometría de Masas , Estructura Molecular , Resonancia Magnética Nuclear Biomolecular , Fenalenos/química , Extractos Vegetales/química , Extractos Vegetales/aislamiento & purificación , Hojas de la Planta/químicaRESUMEN
A series of non-wood plant fibers, namely kenaf, jute, sisal and abaca, have been analyzed upon pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) of the whole material. The pyrolysis products mainly arise from the carbohydrate and lignin moieties of the fibers. The lignin-derived phenols belonged to the p-hydroxyphenylpropanoid (H), guaiacylpropanoid (G) and syringylpropanoid (S) structures, and showed a high S/G ratio of between 2.0 and 5.4, the highest corresponding to kenaf. Among the lignin-derived phenols released, small amounts of sinapyl and coniferyl acetates (in both cis- and trans-forms) were identified for the first time upon Py-GC/MS of lignocellulosic materials. Acetylation of the sinapyl and coniferyl alcohols was at the gamma-position of the side chain. The release of these alcohols derived from intact acetylated lignin units upon pyrolysis seems to indicate that the native lignin in the fibers selected for this study is at least partially acetylated. Sinapyl (and coniferyl) acetates have recently been suggested to be authentic lignin precursors involved in the polymerization of lignin along with the normal sinapyl and coniferyl alcohols. Py-GC/MS will offer a convenient and rapid tool for analyzing naturally acetylated lignins, as well as to screen plant materials for the presence of acetylated units in lignin.