Alkali-soluble Lignin Research Articles

Genetic control of wood physicochemical properties, growth, and phenology in hybrid aspen clones

To better understand the genetic control of wood chemical and fibre properties in hybrid aspen, genetic relationship of these with growth and phenological traits were examined. In all, 18 hybrid aspen clones were sampled in the 13- and 14-year-old clone trials in Sweden. Strong clone within family effects were present for growth and wood properties. The repeatability estimates across two sites were 0.85, 0.65, 0.56, 0.54, and 0.65 for alkali soluble lignin content, arithmetic average fibre length, coarseness, diameter, and height, respectively. Genetic correlations generally exceeded the corresponding phenotypic correlations. The phenotypic and genetic correlations were negative between fibre count and height growth (–0.64 and –0.65, respectively) and between fibre count and length of growth period. The result suggests that the length of the growth period could be a good predictor of clone differences in fibre count. The estimated correlations were unfavourable, in the sense that clonal selection directed at increasing the fibre count is expected to produce an indirect genetic decline in growth. Intersite genetic correlations indicated that wood characters were more stable than growth traits.

Steam-explosion of olive stones: hemicellulose solubilization and enhancement of enzymatic hydrolysis of cellulose

Olive stones (whole stones and seed husks in fragments) were processed by steam-explosion under different experimental conditions of temperature and time, 200–236°C for 2–4 min, with or without previous acid impregnation with 0.1% H 2SO 4 (w/w). This paper examines the solubilization of hemicelluloses and their molecular weight distribution. The subsequent enzymatic hydrolysis of the solid residue, using a preparation of cellulase, was also studied. The maximum yield of the pentosan recovered in the water solution was 63% pentose in the starting material for seed husk treated at 200°C for 2 min (log R 0 3.24) prior to acid-impregnation, or at 215°C for 2 min (log R 0 3.69) without acid, compared to 39% of the potential yield for whole stones pre-impregnated with acid under more severe conditions (at log R 0=4.07). This indicates that the autohydrolysis of hemicellulose in seed husks when compared to whole stones is enhanced. The molecular weight distribution of profile sugars showed that the depolymerization of hemicelluloses is a function of the severity of the treatment. Steam-explosion improved the accessibility of the cellulose and increased the enzymatic hydrolysis yield after steam-explosion with respect to material without steam explosion (ball-milled material), although little increase in the extent of saccharification occurred when the alkali-soluble lignin was removed. Only when the substrate was post-treated with Na-chlorite was the enzymatic hydrolysis improved, the water-insoluble residue being almost completely hydrolyzed in 8 h of incubation.

Physicochemical characterization of lignins from rice straw by hydrogen peroxide treatment

Extraction of the dewaxed rice straw with 1% NaOH at 55°C for 2 h and following treatment without and with 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0% hydrogen peroxide (H2O2) at 45°C for 12 h at pH 11.5 resulted in a dissolution of 68.3, 85.4, 89.4, 92.3, 92.3, 94.3, and 95.1% of the original lignin, respectively. Meanwhile, the two-stage treatment together solubilized 67.2, 77.2, 78.7, 83.7, 85.5, 87.3, and 88.5% of the original hemicelluloses and degraded 2.5, 9.8, 11.8, 12.1, 15.6, 16.4, and 17.8% of the original cellulose under the conditions given, respectively. Analyses of these lignins revealed that alkali-soluble lignin fractions did not suffer sever oxidation, but nearly 60% of the original lignin was dissolved out during the first stage of alkali treatment. In the second stage of alkaline peroxide treatment, the residual lignins were substantially released and enriched in oxidized carbonyl and carboxyl groups. In comparison, the isolated eight pure lignin samples were further characterized by both destructive methods such as alkaline nitrobenzene oxidation and nondestructive techniques such as ultraviolet (UV), Fourier transform infrared (FTIR), and carbon-13 magnetic resonance spectroscopy (13C-NMR) as well as gel permeation chromatography (GPC), and the results are reported. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 719–732, 2001

Fractional isolation and physico-chemical characterization of alkali-soluble lignins from fast-growing poplar wood

This paper examines the physico-chemical properties and structural features of six alkali-soluble lignin preparations extracted with 5, 7.5, and 10% NaOH at 50°C for 4–12 h from fast-growing poplar wood. The pure lignin (PL) preparations were characterized using UV, FT-IR, 13C-NMR, GPC, and alkaline nitrobenzene oxidation methods. The results showed that all the PL fractions are relatively free of associated polysaccharides and are composed of large amounts of syringyl units together with noticeable quantities of guaiacyl and fewer p-hydroxyphenyl units. Their weight-average molecular weights ranged from 4520 to 6900 g mol −1. Noticeable amounts of esterified p-hydroxybenzoic acids, minor quantities of esterified p-coumaric acid, and traces of both ester and ether linked ferulic acids were identified in the isolated lignin preparations. The lignin fraction, extracted with 5% NaOH at 50°C for 12 h from the dewaxed fast-growing poplar wood, is composed mainly of β- O-4 ether bonds together with small amounts of β–β′ and β-5 carbon–carbon linkages between the lignin structural units.

Physicochemical characterization of lignins from rice straw by hydrogen peroxide treatment

Extraction of the dewaxed rice straw with 1% NaOH at 55°C for 2 h and following treatment without and with 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0% hydrogen peroxide (H2O2) at 45°C for 12 h at pH 11.5 resulted in a dissolution of 68.3, 85.4, 89.4, 92.3, 92.3, 94.3, and 95.1% of the original lignin, respectively. Meanwhile, the two-stage treatment together solubilized 67.2, 77.2, 78.7, 83.7, 85.5, 87.3, and 88.5% of the original hemicelluloses and degraded 2.5, 9.8, 11.8, 12.1, 15.6, 16.4, and 17.8% of the original cellulose under the conditions given, respectively. Analyses of these lignins revealed that alkali-soluble lignin fractions did not suffer sever oxidation, but nearly 60% of the original lignin was dissolved out during the first stage of alkali treatment. In the second stage of alkaline peroxide treatment, the residual lignins were substantially released and enriched in oxidized carbonyl and carboxyl groups. In comparison, the isolated eight pure lignin samples were further characterized by both destructive methods such as alkaline nitrobenzene oxidation and nondestructive techniques such as ultraviolet (UV), Fourier transform infrared (FTIR), and carbon-13 magnetic resonance spectroscopy (13C-NMR) as well as gel permeation chromatography (GPC), and the results are reported. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 719–732, 2001

Physicochemical and structural characterization of alkali soluble lignins from oil palm trunk and empty fruit-bunch fibers.

Six alkali soluble lignin fractions were extracted from the cell wall materials of oil palm trunk and empty fruit-bunch (EFB) fibers with 5% NaOH, 10% NaOH, and 24% KOH/2% H(3)BO(3). All of the lignin fractions contained rather low amounts of associated neutral sugars (0.8-1.2%) and uronic acids (1.1-2.0%). The lignin fractions isolated with 5% NaOH from the lignified palm trunk and EFB fibers gave a relatively higher degree of polymerization as shown by weight-average molecular weights ranging between 2620 and 2840, whereas the lignin fractions isolated with 10% NaOH and 24% KOH/2% H(3)BO(3) from the partially delignified palm trunk and EFB fibers showed a relatively lower degree of polymerization, as shown by weight-average molecular weights ranging between 1750 and 1980. The results obtained by alkaline nitrobenzene oxidation showed that all of the lignin preparations contained a high proportion of noncondensed syringyl units with small amounts of noncondensed guaiacyl and fewer p-hydroxyphenyl units. The lignin fraction extracted with 5% NaOH from the lignified EFB fiber was mainly composed of beta-O-4 ether-linked units. Small amounts of 5-5', beta-5, and beta-beta' carbon-carbon linkages were also found to be present between the lignin structural units. Further studies showed that uronic, p-hydroxybenzoic, and ferulic acids in the cell walls of palm fibers were esterified to lignin.

Physico-chemical and Structural Characterization of Alkali-soluble Lignins from Sugar Beet Pulp

Two alkali-soluble lignin fractions were extracted from wax, protein, and pectin free cell wall residues of sugar beet pulp with 10% KOH and 7.5% NaOH both at 15°C for 16 h. The physico-chemical properties and structural features of the two isolated pure lignin fractions (LA) were characterized by UV, FT-IR, and 13C-NMR spectroscopy. Both of the lignin fractions contain rather low amounts of neutral sugars (0.89-1.03%) and pectic substances (1.75-1.80%). Their molecular-average weights ranged between 1830-1920 Da. The results obtained by alkaline nitrobenzene oxidation showed that the two lignins contain large amounts of non-condensed guaiacyl units, together with only a few non-condensed syringyl and p-hydroxyphenyl units. The lignin fraction, isolated by 7.5% NaOH at 15°C for 16h, is mainly composed of β-O-4 ether bonds. The less common β-β, β-5, β-1, and 5-5′ carbon-carbon linkages are also found to be present between the lignin structural units. Further studies suggested that hydroxycinnamic acids, such as p-coumaric and ferulic acids, and galacturonic acid are tightly linked to lignin molecules.

Fractionation of Wheat Straw by Steam-Explosion Pretreatment and Alkali Delignification. Cellulose Pulp and Byproducts from Hemicellulose and Lignin

The fractionation of wheat straw was studied using a two-stage process based on an hydrolytic pretreatment followed by alkali delignification. The hydrolytic pretreatment was performed by steam explosion. Straw was steamed at temperatures comprised between 205 and 230°C for 2 min. The steamed straw was washed with hot water to yield a solution rich in hemicellulose-derived mono- and oligosaccharides. The washed fiber was delignified by alkali at 160°C for 60 min using a NaOH load of 20%. The alkali-soluble lignin was recovered by filtration after acidification of the black liquor. The delignified pulp was screened and bleached to produce viscose-grade cellulose. The optimization of the pretreatment conditions led to the following results at a pretreatment severity of log(R0) = 3.80: yield of viscose-grade cellulose = 70% of the potential; lignin recovery = 70% of the Klason lignin present in the untreated straw; hemicellulose sugars = 55% of the potential, recovered as molasses.

Physico-Chemical and Thermal Characterization of Alkali-Soluble Lignins from Wheat Straw

Four alkali-soluble lignin fractions were extracted from dewaxed wheat straw with 3% sodium hydroxide at 45°C for 2, 5, 12, and 15 h, respectively. The pure alkali-soluble lignin preparations LA were obtained by using a two step precipitation method instead of the traditional ether precipitation procedure. The physico-chemical properties and structural features of the isolated pure lignin fractions were characterized by UV, FT-IR, 13C NMR spectroscopy, and thermal analysis. The lignin in fraction LA-1 is mainly composed of β-O-4 ether bonds. The less common β-5 and β-β carbon-carbon linkages are also present in the lignin structural units. The results obtained showed that the lignin fractions appeared to be strongly associated to hydroxycinnamic acids such as p-coumaric and ferulic acids and glucuronic acid or 4-O-methylglucuronic acid.

Steam-assisted biomass fractionation. I. Process considerations and economic evaluation

A series of process design and economics models have been created which calculate the process cost for several scenarios in steam-explosion/fractionation of wood. Steam-explosion/fractionation technology offers the opportunity to produce chemicals and materials from such biomass resources as wood processing residues, agricultural crop residues and waste paper. The models comprise a series of modular computer simulations, where each module summarizes a particular group of unit operations with respect to mass balance, energy requirements, and process cost including utilities, capital, labor, and other related costs. These modules are compiled into three groups of scenarios: (1) unprocessed steam-exploded biomass, (2) water extracted steam-exploded biomass, and (3) water and aqueous solvent (alkali or ethanol) extracted steam-exploded biomass. For the base case evaluated, the cost of producing a 50% moisture content (based on total weight) steam-exploded fiber amounts to the raw material cost plus $0.077 kg −1, dry basis. A water washed steam-exploded biomass fiber along with water-soluble solids (WSS) can be produced for $0.165 kg −1, plus raw material, if the WSS are recovered by evaporative concentration. A more delignified, steam-exploded fiber with recovery of WSS and an aqueous alkali soluble lignin can be produced for between $0.222 and $0.246 kg −1 of raw material processed, dry basis, depending on the lignin recovery option employed (i.e. evaporative concentration; precipitation from alkaline solution; or spray drying).

Fractionation and Characterization of Alkali-Soluble Lignins from Wheat Straw

The chemical compositions of seven alkali-soluble lignin fractions isolated from partly dewaxed wheat straw with sodium hydroxide at successively increasing strength from 0.125 to 1.50 M are reported. The physico-chemical properties of the lignin fractions were characterized by using GPC-, UV-, IR-, 13C-NMR- spectroscopy and alkaline nitrobenzene oxidation. No significant difference in monomeric composition was found in the case of wheat straw lignin fractions. However, more condensed fractions were found to be LA 4-7 and less condensed fractions appeared between fractions LA-1 and LA-3. A method of two steps of precipitation was proposed in this study to obtain the lignin fractions relatively free of polysaccharides. The isolated lignin fractions contained rather low amount of polysaccharides (1.7–1.9%), and had low molecular-average weight between 1281 and 1796. It was found that p-coumaric acid is ester-linked to lignin at C-α and C-γ, while most of the ferulic acids are ether-linked to lignin at C-α and C-γ.

Fractional Isolation and Physico-Chemical Characterization of Alkali-Soluble Lignins from Wheat Straw

Six alkali-soluble lignin fractions were sequentially extracted from partially dewaxed wheat straw with sodium hydroxide at increasing strength from 0.25 to 2.00M, and the chemical compositions are reported. The physico-chemical properties of the lignin fractions were characterized by nitrobenzene oxidation, and UV-, IR-, and 13 C-NMR spectroscopy. A new method of two step precipitation was proposed in this study to obtain lignin fractions relatively free of polysaccharides. It was found that 60.8 %. wheat straw lignin was released during the above alkali treatments at 30°C. The isolated lignin fractions contained very small amounts of polysaccharides, 1.4-1.7%, and had low molecular-average weights between 1200 and 1560. They are more condensed than the typical hardwood or softwood lignins.

Effects of pretreatment temperature and alkali concentration on the composition of alkali‐soluble lignins from wheat straw

A new rapid method of two step precipitation for isolation of alkali-soluble lignins with relatively free of polysaccharides from wheat straw was proposed in this study. The isolated alkali-soluble lignin fractions LA contained rather low amounts of neutral sugars (0.7–1.0%) and had low average molecular weights (960–1440 Da). The isolated lignin fractions LA contained roughly equal amounts of guaiacyl (G) and syringly (S) units with relatively fewer p-hydroxyphenyl (H) units, and appeared to be closely associated to phenolic acids and glucuronic acid or 4-O-methylglucuronic acid. The chemical compositions in each of the fractions are reported. The physico-chemical properties and structure features of these lignin fractions LA were characterized by UV-, IR-, 13C-NMR-spectroscopy, and alkaline nitrobenzene oxidation. © 1996 John Wiley & Sons, Inc.

Changes in the Phenolic Composition of Maize Stovers after Blooming

The phenolic composition of 10 samples of maize stovers collected every 7 days after blooming was determined by high-performance liquid chromatography with electrochemical detection (HPLC-ED) and pyrolysis/gas chromatography/mass spectrometry (PY/GC/MS). An increase of the p-hydroxycinnamic acids (i.e., p-coumaric acid and ferulic acid) with maturation was observed by HPLC-ED of mild alkaline extracts. Likewise, vanillin and syringaldehyde, i.e., the typical aldehydes constituting lignin, showed an increase with maturation in the alkali-soluble lignin fraction, as determined by HPLC-ED after nitrobenzene oxidation. As to PY/GC/MS, a less marked variation in the typical lignin units was observed with ripening. The ratios between syringyl and guaiacyl lignin units as determined by both analytical techniques were higher, but of the same order, than those determined previously in a set of maize stovers sampled over a wider range of maturation. Keywords: Maize stover; phenolics; lignin; high-performance liquid...

Acid detergent dispersible lignin in tropical grasses

AbstractThe detergent system of analysis partitions lignin into two fractions: acid detergent lignin (ADL), usually equated with forage lignin, and ‘acid detergent dispersible lignin’ (ADDL), the existence of which has scarcely been recognized, but can be higher than ADL in tropical grasses. For nine species ADL and ADDL as percentage of original dry matter were, respectively: Aristides calcyna. 8.9 and 9.8; Astrebla squarrosa, 8.6 and 14.7; Chloris gayana, 3.9 and 6.7; Eragrostis sp, 4.3 and 8.8; Heteropogon eontorius, 3.9 and 10.4; Iseilema membranaceum 7.2 and 8.2; Panicum maximum, 1.8 and 5.7; Themeda triandra, 7.3 and 8.2; Sorghum sp, 3.4 and 13.8. Tropical legumes (four species) had much lower levels of ADDL. Azo‐stained fibre showed that most of the free phenolic functions and the alkali‐soluble lignin were in the ADDL fraction. The difference between grasses and legumes was so marked that azo‐staining may provide a method for distinguishing grass and legume particles in feed or faecal samples. The apparent discrepancies between grasses and legumes in the effect of lignin on digestibility may be explained by the grass lignin having been grossly underestimated as ADL. When Heteropogon contortus and Astrebla squarrosa were incubated in dacron bags in the rumen the ratio of ADDL to ADL in the residual fibre decreased markedly in the first 48 h, indicating a higher apparent digestibility for ADDL. From feeding experiments with sheep the apparent digestibility of ADL and ADDL were 18 and 38% for Astrebia squarrosa and 14 and 26% for Stylosanthes hamata. As isolated lignin corresponding to ADDL was inhibitory in vitro to a mixed rumen microbial population at a concentration of 0.12 mg ml−1. Measurement of ADDL could easily be included in fibre analysis by the sequential detergent method as it would require only UV absorbance measurement on the acid detergent filtrate. This would allow measurement of total lignin within the existing system.

Biological variability in lignification of maize: Expression of the brown midrib bm2 mutation

AbstractThe cell wall phenolic components in the internodes of three maize genotypes, namely normal, bm2 and bm3 maize, were determined. The bm2 and bm3 brown midrib mutations lowered the lignin content of the bottom, middle and top internodes to a similar extent. However, unlike bm3, the bm2 trait did not induce a sharp reduction of the level of ester‐bound p‐coumaric acid in maize internodes. The other main alkali labile phenolic acid, ferulic acid, reached similar levels in the three genotypes. The main difference between bm2 and bm3 mutations occurred in the alkyl aryl ether linked structures of the lignin component. In contrast to bm3 lignins, which are characterised by a low syringyl content, the bm2 lignin had a lower content of guaiacyl units than lignin of normal maize internode. Consequently, the syringyl/guaiacyl molar ratio of bm2 lignin gave higher values (2.7–3.2) than those from either normal (0.9–1.5) or bm3 lignins (0.3). The alkali solubility of lignin was also compared between the three genotypes. Incorporation of the bm3 trait in maize led to a high recovery of alkali soluble lignin whereas the bm2 lignin had a similar solubility to the normal one in 2 M NaOH. The monomeric composition of the alkali soluble lignins was consistent with the non‐condensed structures of the in‐situ polymer. Although the bm3 and bm2 mutations had different effects on lignification, the modification of the cell wall phenolic level was also found in the bm2 maize stem as previously studied.

カカオリグニン摂取が高血圧自然発症ラットの血圧および血しょう脂質に及ぼす影響

Lignin is a kind of insoluble dietary fiber. Cacao contains about 10% lignin, but effect of cacao lignin is not studied. We prepared cacao lignins from defatted cocoa powder by two methods Klason lignin (KL) was prepared by the Klason method with concentrated H2SO4 Alkali soluble lignin (ASL) was extracted with 1% NaOH solution. Their effects on blood pressure and lipid metabolism were studied in spontaneously hypertensive rats (SHR). Adult male SHR were kept on a diet of semipurified feed containing 1% NaCl and 2% KL, ASL, or cholestyramine (CL) for 19 days. The mean blood pressure of the control increased. The mean blood pressure of groups fed KL, ASL, or CL was significantly lower than that of the controls on days 10 and 15 of the diet. The plasma Na/K ratio of groups fed KL, ASL, or CL was lower than in the control group at day 15. There were no significant differences in the mineral balance of cations. Fecal excretion of Na was increased in groups fed KL, ASL, or CL compared with the control group, and fecal excretion of K was increased in the KL group compared with the control group. Fecal excretion of Ca and Mg did not increase in the KL, ASL, or CL groups compared with the control group. The plasma level of total cholesterol in the KL group was significantly lower than that of the control groups at days 7 and 15. The ability of lignins to adsorb bile acids depended on the pH in vitro, on the other hand the ability of CL to adsorb bile acids did not depend on the pH. These results suggest that cacao lignins may suppress lncreases in blood pressure and plasma levels of total cholesterol.

Lignocellulose degradation and subsequent metabolism of lignin fermentation products by the desert black Bedouin goat fed on wheat straw as a single-component diet.

Bedouin goats were fed on wheat straw as a single-component diet under two watering regimens, drinking once daily or once every 4 d, in order to clarify whether lignin-degradation products were absorbed, metabolized and excreted in urine. Acid-soluble lignin accounted for 220 g/kg total lignin, its digestibility was the highest (0.87) and was unaffected by water deprivation. Acid-insoluble lignin accounted for 780 g/kg total lignin and its digestibility increased during water deprivation from 0.21 to 0.41. Alkali-soluble lignin accounted for 320 g/kg total lignin and its digestibility increased during water deprivation from 0.44 to 0.53. Digestibility of structural carbohydrate was considerably higher than that observed in other domesticated ruminants fed on wheat straw. It responded positively to water deprivation, increasing from 0.63 to 0.73 with cellulose and from 0.61 to 0.68 with hemicellulose. The amount of urinary aromatic acids, mainly in the form of hippuric acid, considerably exceeded the potential contribution of any non-lignin component which might affect the excretion of aromatic acids. A considerable percentage (71-76) of the apparently digested lignin was not accounted for as soluble phenolic compounds in faeces or as aromatic acids in urine, and hence was apparently completely metabolized. Lignin is a key substrate which is extensively digested in goats fed on low-quality forage, with subsequent absorption of endproducts. This enhanced the availability of structural carbohydrates for fermentation and was associated with excretion of high-energy metabolites in the form of benzoic and hippuric acids.

Assessment of pretreatment conditions to obtain fast complete hydrolysis on high substrate concentrations

Steam-heating of aspen wood chips improved the enzymatic digestibility of the cellulose. Scaling up the reaction vessel from 2 to 60 L had virtually no influence on the chemical composition and the accessibility of the lignocellulosic substrate. Over 85% of the cellulose could be hydrolyzed to glucose when an 8% substrate concentration was used. The residual content of alkali-insoluble lignin appeared to control the digestibility of the cellulose. Increased delignification either by prolonged steaming, oxidative posttreatment, or SO2 catalysis improved the accessibility of the cellulose. The use of SO2 as a catalyst also increased the recovery yield of the wood after steam-heating, with more than 70% of the original xylan recovered as monomeric xylose. Conversion yields of above 90% were achieved at low levels of filter paper activity after a relatively short incubation time. Removal of alkali-soluble lignin did not influence digestibility when the enzyme concentration was based on the cellulose content of the substrates.

Disappearance of Hemicellulosic Monosaccharides and Alkali-Soluble Phenolic Compounds of Normal and Brown Midrib Sorghum × Sudangrass Silages Fed to Holstein Steers

Four ruminally cannulated Holstein steers fed ad libitum were used in a 4×4 Latin square design. Feeds were normal and brown midrib genotypes of Redlan×Piper and Redlan×Greenleaf sorghum-sudangrasses. An in situ trial was run in conjuction with the digestibility trial as part of the data collection for each period. Hemicellulosic monosaccharide and alkali-soluble lignin phenolic compound disappearances were quantitated. The xylose to arabinose ratio was higher in normal genotypes than in brown midribs.Normal genotypes had higher concentrations of alkali-soluble p-coumaric acid and lower vanillin, vanillic acid, and sinapic acid than did brown midrib mutants. Disappearance of p-coumaric acid was higher in steers consuming normal genotypes than in those consuming brown midribs. Neutral detergent fiber, acid detergent fiber, hemicellulose, cellulose, and acid detergent lignin showed no genotypic differences in rate of digestion, but extent of 72h digestion was higher for brown midrib mutants than for normal genotypes. Extent of digestion of the hemicellulosic monosaccharides, xylose, and uronic acids was higher in situ for brown midrib silages compared with normal genotypes. Differences in alkali-soluble phenolic compound and cell wall monosaccharide profiles between normal and brown midrib genotypes may help explain digestibility differences between the two genotypes.