Lignin Units Research Articles

Lignification in developing culms of bamboo Sinobambusa tootsik

Bamboos are among the largest woody grasses and grow very rapidly. Although lignin is a crucial factor for the utilization of bamboo biomass, the lignification mechanism of bamboo shoots is poorly understood. We studied lignification in the bamboo Sinobambusa tootsik during culm development. Elongation growth began in May and ended in late-June, when the lignin content was approximately half that in mature culms. Thioacidolysis analysis indicated that p-hydroxyphenyl units in lignin formed even at late stages of lignification. The syringyl/guaiacyl ratio varied during culm development. Various lignin precursors were detected in developing culms by liquid chromatography–mass spectrometry. The ferulic acid content decreased from May to June, indicating that ferulic acid was utilized in early stages of cell wall formation. Monolignol glucosides were detected at early stages of lignification, whereas the contents of monolignols, coniferaldehyde, sinapaldehyde, p-coumaric acid, and ferulic acid peaked at later stages of lignification. Therefore, lignin precursors may be supplied differentially during the lignification process. In August, the rate of lignification decreased, although the contents of various lignin precursors peaked, implying that the rate-limiting step in the cessation of lignification in bamboo is transport or polymerization of lignin precursors, rather than their biosynthesis.

SbCOMT (Bmr12) is involved in the biosynthesis of tricin-lignin in sorghum.

Lignin in plant biomass represents a target for engineering strategies towards the development of a sustainable bioeconomy. In addition to the conventional lignin monomers, namely p-coumaryl, coniferyl and sinapyl alcohols, tricin has been shown to be part of the native lignin polymer in certain monocot species. Because tricin is considered to initiate the polymerization of lignin chains, elucidating its biosynthesis and mechanism of export to the cell wall constitute novel challenges for the engineering of bioenergy crops. Late steps of tricin biosynthesis require two methylation reactions involving the pathway intermediate selgin. It has recently been demonstrated in rice and maize that caffeate O-methyltransferase (COMT) involved in the synthesis syringyl (S) lignin units derived from sinapyl alcohol also participates in the synthesis of tricin in planta. In this work, we validate in sorghum (Sorghum bicolor L.) that the O-methyltransferase responsible for the production of S lignin units (SbCOMT / Bmr12) is also involved in the synthesis of lignin-linked tricin. In particular, we show that biomass from the sorghum bmr12 mutant contains lower level of tricin incorporated into lignin, and that SbCOMT can methylate the tricin precursors luteolin and selgin. Our genetic and biochemical data point toward a general mechanism whereby COMT is involved in the synthesis of both tricin and S lignin units.

Products of hydrothermal treatment of lignin and the importance of ortho-directed repolymerization reactions

Alkaline hydrothermal treatment (HTT) of Protobind 1000 lignin was studied to improve the understanding of lignin conversion paths. HTT was performed at 300°C using NaOH as base catalyst. Product separation by acidification and solvent fractionation resulted in a liquid product of low molecular mass and narrow molecular mass distribution and two high molecular mass solid fractions. Twenty volatile compounds accounted for about 36wt% of the liquid product, however, the analysis by liquid injection GC–MS was estimated to detect only about 12wt% of the total products. Analytical pyrolysis was applied to investigate the pyrolyzable fraction of the liquid product and the high molecular mass fractions. The pyrolyzable mass accounted for 49wt% of the total products. The liquid product was quantitatively pyrolyzed at 500°C (91±10wt%) while less than half of the high molecular mass fractions were pyrolyzed. Several chemical features of the pyrolysates suggested that ortho-directed alkylation and condensation reactions of phenolate ions were important for the production of oligomeric and polymeric aromatic compounds during HTT. Increased abundancy of hydroxyphenyl and o-alkyl aromatic pyrolysates in the high molecular mass fractions suggested that the syringyl units of the raw lignin were less affected by repolymerization reactions than hydroxyphenyl and guaiacyl units. These results suggest that the monolignol composition of lignin is an important factor for the valorization of lignin by alkaline hydrothermal treatment.

Catalytic depolymerization of organosolv sugarcane bagasse lignin in cooperative ionic liquid pairs

Lignin has been considered as a promising sustainable feedstock for high value-added aromatic chemical production. Here, we propose a novel and efficient process for lignin depolymerization in the presence of cooperative ionic liquid pair, which affords excellent catalytic activity and char inhibition capability. Under the optimized reaction condition, 66.7% lignin conversion is achieved, yielding 14.5wt.% phenolic monomer, numerous volatile products (identified by GC–MS) and negligible char formation. The structural evolution of the sugarcane lignin was intensively investigated via comparative characterization of raw and regenerated lignin using HSQC, 1H NMR, FT-IR, GPC and elemental analysis. All three structural lignin units are degraded in this process, where, H-lignin is found to be the most susceptible. Satisfactory lignin depolymerization performance was found for the cooperative ionic liquid system, even after the fifth run, demonstrating a reasonable reusability.

Structural Characteristics of Bagasse Furfural Residue and Its Lignin Component. An NMR, Py-GC/MS, and FTIR Study

Commercial furfural, an important platform chemical, is produced from acid hydrolysis of lignocellulosic biomass. The manufacturing processes are inherently inefficient, and so it is necessary to value add to substantial amounts of residue obtained. The structural features of bagasse furfural residue and the lignins extracted from it by three NaOH treatments have been studied in order to understand the transformations that occurred by these treatments. 2D-NMR and Py-GC/MS of the furfural residue revealed that it contains mostly lignin and depolymerized cellulose moieties and the complete absence of xylans as a result of their hydrolysis during the furfural production process. In addition, the analyses revealed that the furfural residue contains 44% of H-type lignin units, in comparison to 11% for bagasse, and most of the lignin interunit linkages present in bagasse have disappeared. The pyrograms show that the furfural residue produced unusually high phenol content, which was attributed to the high levels...

Disrupting Flavone Synthase II Alters Lignin and Improves Biomass Digestibility.

Lignin, a ubiquitous phenylpropanoid polymer in vascular plant cell walls, is derived primarily from oxidative couplings of monolignols (p-hydroxycinnamyl alcohols). It was discovered recently that a wide range of grasses, including cereals, utilize a member of the flavonoids, tricin (3',5'-dimethoxyflavone), as a natural comonomer with monolignols for cell wall lignification. Previously, we established that cytochrome P450 93G1 is a flavone synthase II (OsFNSII) indispensable for the biosynthesis of soluble tricin-derived metabolites in rice (Oryza sativa). Here, our tricin-deficient fnsII mutant was analyzed further with an emphasis on its cell wall structure and properties. The mutant is similar in growth to wild-type control plants with normal vascular morphology. Chemical and nuclear magnetic resonance structural analyses demonstrated that the mutant lignin is completely devoid of tricin, indicating that FNSII activity is essential for the deposition of tricin-bound lignin in rice cell walls. The mutant also showed substantially reduced lignin content with decreased syringyl/guaiacyl lignin unit composition. Interestingly, the loss of tricin in the mutant lignin appears to be partially compensated by incorporating naringenin, which is a preferred substrate of OsFNSII. The fnsII mutant was further revealed to have enhanced enzymatic saccharification efficiency, suggesting that the cell wall recalcitrance of grass biomass may be reduced through the manipulation of the flavonoid monomer supply for lignification.

Lignification of Sheepgrass Internodes at Different Developmental Stages and Associated Alteration of Cell Wall Saccharification Efficiency.

Sheepgrass (Leymus chinensis) is a high-quality cool-season forage crop used as pasture and hay for livestock feeds. The presence of lignin in cell walls, however, impairs forage digestibility of such lignocellulosic feedstock. Here, the structural characterization and cell wall composition of sheepgrass internodes were studied, and a progressive increase in cell wall lignification was observed with internode maturation. Lignin composition analysis further revealed a gradual accumulation of guaiacyl and syringyl lignin units during internode development. Consistently, the transcript abundance of lignin-related genes was upregulated in mature internodes, suggesting their potential roles in lignin biosynthesis. Furthermore, the effects of cell wall composition and lignification extent on biomass saccharification efficiency were examined in sheepgrass. The results showed that lignin content, guaiacyl and syringyl lignin unit levels inversely correlated with cell wall digestibility, indicating that lignin is a crucial obstacle for utilizing sheepgrass feedstock. The baseline information obtained in this work will facilitate establishment, grazing management, harvesting and feedstock utilization of sheepgrass in future.

Litter quality control of decomposition of leaves, twigs, and sapwood by the white-rot fungus Trametes versicolor

Litter quality plays predominant roles in plant litter decomposition by modifying the activity of decomposer fungi, but little is known about the response of the decomposing activity of individual fungal strains to variations in litter quality. In the present study, the variability in the decomposing ability of a single fungal strain (Trametes versicolor IFO30340) was quantified under pure culture conditions to elucidate litter quality measures that control the decomposition. We used a total of 72 litters from 51 plant species, including leaves, twigs, sapwood, bark, heartwood, and petioles of broad-leaved trees, coniferous trees, and grass. Mass loss of litter caused by the fungus ranged from 0.9 to 59.8% of the original litter mass, was significantly higher in leaves, twigs, and petioles than in heartwood, and was significantly higher in broad-leaved than in coniferous litter. Tissue type (leaf, sapwood, or twig) and the relative amount of acid-unhydrolyzable residues to total nitrogen were selected as predictor variables of the mass loss of litters. Fourier transform infrared (FT-IR) spectroscopy showed that guaiacyl units of lignin negatively affected the fungal decomposition.

Characterization and enzymatic hydrolysis of wood from transgenic Pinus taeda engineered with syringyl lignin or reduced lignin content

Softwood is an abundant resource; however, currently its utilization for bioconversion to obtain platform sugars is limited. Pinus taeda trees which were genetically modified to either produce S lignin or to decrease lignin content were characterized with a suite of analytic techniques. Syringyl lignin was visualized in the secondary xylem of one genetic line with Maule staining. Solid-state nuclear magnetic resonance identified the S lignin units were coupled into the lignin through β-O-4 linkages, and thioacidolysis measured approximately 13% S lignin content in the same sample. Reductions of the lignin of as much as 33% were observed in the transgenics. To better understand how these modifications affect bioconversion, their amenability to hot water and dilute acid pretreatments and enzymatic hydrolysis was evaluated. Lignin reductions resulted in 1.9–3.2-fold increases in glucose release compared to the control. However, no apparent benefit was observed by S lignin incorporation at the concentrations reported in this study. These results highlight the potential for softwood cell wall properties to be improved for bioenergy/biochemical applications.

Lignin-Derived Thioacidolysis Dimers: Reevaluation, New Products, Authentication, and Quantification.

Lignin structural studies play an essential role both in understanding the development of plant cell walls and for valorizing lignocellulosics as renewable biomaterials. Dimeric products released by selectively cleaving β–aryl ether linkages between lignin units reflect the distribution of recalcitrant lignin units, but have been neither absolutely defined nor quantitatively determined. Here, 12 guaiacyl‐type thioacidolysis dimers were identified and quantified using newly synthesized standards. One product previously attributed to deriving from β–1‐coupled units was established as resulting from β–5 units, correcting an analytical quandary. Another longstanding dilemma, that no β–β dimers were recognized in thioacidolysis products from gymnosperms, was resolved with the discovery of two such authenticated compounds. Individual GC response factors for each standard compound allowed rigorous quantification of dimeric products released from softwood lignins, affording insight into the various interunit‐linkage distributions in lignins and thereby guiding the valorization of lignocellulosics.

Effects of Solvation and Ionization on 13C NMR Spectra of Lignin Model Compounds, Spruce Milled Wood Lignin and Kraft Lignin

The effects of alkali and polar aprotic solvent on the aromatic carbons signals in 13C NMR (Carbon-13 nuclear magnetic resonance) spectra of lignin model compounds and spruce milled wood lignin (MWL) were studied. It was found that in 1 M aqueous NaOH signal shifts of C-1 and C-4 carbon atoms in the aromatic ring were the most noticeable in lignin models with free phenolic hydroxyl groups, which are ionized under the conditions. A similar effect in the spectra of the studied model compounds was observed in 0.5 M aqueous NaOD-deuterated dimethyl sulfoxide (DMSO) mixture (DMSO: water ratio 3:7 v/v). The model data help explaining changes in the 13C NMR spectra of MWL and lignin in situ dissolved in spruce kraft black liquor caused by ionization. In the 13C NMR spectra of spruce black liquor the signals of phenolic and non-phenolic lignin units are clearly separated and do not overlap with the signals of the carbon atoms of carbohydrates and other aliphatic products of wood degradation. The data obtained are useful in understanding the important role of solvation and ionization processes leading to lignin solubilization.

Solubility of Lignin and Acetylated Lignin in Organic Solvents

The solubility of four lignin samples and their acetylated forms was determined in a series of organic solvents to investigate the relationship between solubility and the solubility parameter. The solubility parameter of lignin samples and acetylated lignin was calculated based on the number of atoms or groups on lignin units. Lignin samples were obtained by isolating lignin from lignocellulosic bioethanol residues (Lignin 1 [L1]), isolating lignin from kraft hardwood black liquor (Lignin 2 [L2]), commercial kraft softwood lignin (Lignin 3 [L3]), and commercial soda non-wood lignin (Lignin 4 [4]). The solubility of lignin in organic solvents was not predictable due to poor correlation between the solubility of lignin and its solubility parameter. However, the solubility of lignin in an organic solvent depended on the molecular weight and the aliphatic hydroxyl number of the lignin. L2, with a lower molecular weight than other lignin samples, had the highest solubility in organic solvents, and L3, with highest aliphatic hydroxyl number, had the lowest solubility in organic solvents. All acetylated lignins were soluble in most of the organic solvents. Furthermore, the molecular weights of the soluble parts of all four lignins in ethyl acetate were found to be lower than the original lignins.

Assessment of the thermal behavior of lignins from softwood and hardwood species

The thermal behavior of lignins from softwood and hardwood species has been investigated using thermogravimetry and differential scanning calorimetry. Klason Lignin from Pinus taeda and Klason lignin from Eucalyptus grandis were studied. The differential scanning calorimetry results showed that both Klason lignins studied presented similar glass transition temperature. Thermogravimetric results showed that the lignin degradation occurs in three stages. The Klason lignin of Pinus taeda is more thermally stable than Eucalyptus grandis, probably because of the higher thermal stability of the guaiacyl units in softwood lignin. The degradation of both lignins initiate by a diffusion process. However when the conversion values are higher than 0,1 the lignin degradation mechanism is a complex procedure and involves the degradation of a highly condensed aromatic structure formed at the previous degradation stages.

Effect of torrefaction temperature on lignin macromolecule and product distribution from HZSM-5 catalytic pyrolysis

Torrefaction is a low-temperature process considered as an effective pretreatment technique to improve the grindability of biomass as well as enhance the production of aromatic hydrocarbons from Catalytic Fast Pyrolysis (CFP). This study was performed to understand the effect of torrefaction temperature on structural changes in the lignin macromolecule and its subsequent influence on in-situ CFP process. Lignin extracted from southern pine and switchgrass (via organosolv treatment) was torrefied at four different temperatures (150, 175, 200 and 225°C) in a tubular reactor. Between the two biomass types studied, lignin from pine appeared to have greater thermal stability during torrefaction when compared with switchgrass lignin. The structural changes in lignin as a result of torrefaction were followed by using FTIR spectroscopy, solid state CP/MAS 13C NMR, 31P NMR spectroscopy and it was found that higher torrefaction temperature (200 and 225°C) caused polycondensation and de-methoxylation of the aromatic units of lignin. Gel permeation chromatography analysis revealed that polycondensation during torrefaction resulted in an increase in the molecular weight and polydispersity of lignin. The torrefied lignin was subsequently used in CFP experiments using H+ZSM-5 catalyst in a micro-reactor (Py-GC/MS) to understand the effect of torrefaction on the product distribution from pyrolysis. It was observed that although the selectivity of benzene-toluene-xylene compounds from CFP of pine improved from 58.3% (torrefaction temp at 150°C) to 69.0% (torrefaction temp at 225°C), the severity of torrefaction resulted in a loss of overall aromatic hydrocarbon yield from 11.6% to 4.9% under same conditions. Torrefaction at higher temperatures also increased the yield of carbonaceous residues from 63.9% to 72.8%. Overall, torrefying lignin caused structural transformations in both type of lignins (switchgrass and pine), which is ultimately detrimental to achieving a higher aromatic hydrocarbon yield from CFP.

Micropyrolysis of natural poplar mutants with altered p-hydroxyphenyl lignin content

Analytical pyrolysis coupled to GC–MS (Py-GC–MS) was applied for the thermochemical degradation analysis of wood from poplar (Populus nigra) defective in p-HYDROXYCINNAMOYL-CoA:SHIKIMATE p-HYDROXYCINNAMOYL TRANSFERASE 1 (HCT1), an enzyme essential in the biosynthesis of guaiacyl and syringyl units in lignin. The aim of this study was to assess the potential of natural poplar trees with characteristic lignin composition to improve the yield of valuable chemicals in biomass fast pyrolysis, with a focus on phenolic product formation during lignin decomposition. Analysis of the fast pyrolysis vapor phase obtained from the lignocellulosic biomass of trees homozygous for the defective PnHCT1-Δ73 allele revealed significant shifts in the spectrum of lignin-derived pyrolytic compounds as compared to wild type and heterozygous trees. More particular for the homozygotes, a higher production of the non-methoxylated p-hydroxycinnamic alcohol (p-coumaryl alcohol) and 2,3-dihydrobenzofuran was detected at the expense of mono-methoxylated phenols. Correlation analysis also suggested further decomposition reactions such as demethoxylation, demethylation and alkylation of the mono- and di-methoxylated phenolic moieties during pyrolysis, giving rise to a remarkable amount of non-methoxylated phenols in the pyrolytic spectrum.

Selective ligninolysis of wheat straw and wood chips by the white-rot fungus Lentinula edodes and its influence on in vitro rumen degradability.

BackgroundThe present work investigated the influence of lignin content and composition in the fungal treatment of lignocellulosic biomass in order to improve rumen degradability. Wheat straw and wood chips, differing in lignin composition, were treated with Lentinula edodes for 0, 2, 4, 8 and 12 wk and the changes occurring during fungal degradation were analyzed using pyrolysis-gas chromatography-mass spectrometry and detergent fiber analysis.ResultsL. edodes preferentially degraded lignin, with only limited cellulose degradation, in wheat straw and wood chips, leaving a substrate enriched in cellulose. Syringyl (S)-lignin units were preferentially degraded than guaiacyl (G)-lignin units, resulting in a decreased S/G ratio. A decreasing S/G ratio (wheat straw: r = −0.72, wood chips: r = −0.75) and selective lignin degradation (wheat straw: r = −0.69, wood chips: r = −0.88) were correlated with in vitro gas production (IVGP), a good indicator for rumen degradability.ConclusionsL. edodes treatment increased the IVGP of wheat straw and wood chips. Effects on IVGP were similar for wheat straw and wood chips indicating that lignin content and 3D-structure of cell walls influence in vitro rumen degradability more than lignin composition.

Determination of Phenolic Hydroxyl Groups in Technical Lignins by Ionization Difference Ultraviolet Spectrophotometry (∆ε-IDUS method)

The amount of hydroxyl groups, particularly phenolic, is one of the most important parameters in lignins, as it is an indicator of lignin reactivity. Ultraviolet (UV) Spectrophotometry is a simple and inexpensive method for determining phenolic hydroxyls in lignin. Ionization Difference Ultraviolet Spectrophotometry (Δe-method) relies on the analysis of solubilized lignin at neutral and alkaline conditions with a UV spectrophotometer. We added a slope analysis to the ∆e-method and dubbed the resulting method ∆e-IDUS (Ionization Difference UV Spectrophotometry). We assessed the reliability of ∆e-IDUS by studying the well-known Indulin AT lignin. Additionally, ∆e-IDUS was applied to a previously uncharacterized milox lignin. When compared to 13 C-NMR, ∆e-IDUS underestimated the amount of phenolic hydroxyls for Indulin AT, possibly due to neglecting second phenolic hydroxyls in some lignin units, which resist ionization because of steric hindrance. Nevertheless, the results agreed with previously reported values and confirm that ∆e-IDUS is useful to screen lignins based on their phenolic hydroxyl group content.

Effect of compression combined with steam treatment on the porosity, chemical compositon and cellulose crystalline structure of wood cell walls

The changes of porosity, chemical composition and cellulose crystalline structure of Spruce (Picea abies Karst.) wood cell walls due to compression combined with steam treatment (CS-treatment) were investigated by nitrogen adsorption, confocal Raman microscopy (CRM) and X-ray diffraction (XRD), respectively. A number of slit-shaped mesopores with a diameter of 3.7nm was formed for the CS-treated wood, and more mesopores were found in the steam-treated wood. CRM results revealed cellulose structure was affected by treatment and β-aryl-ether links associated to guaiacyl units of lignin was depolymerized followed by re-condensation reactions. The crystallinity index (CrI) and crystallite thickness (D200) of cellulose for CS-treated wood were largely increased due to crystallization in the semicrystalline region. Higher degree of increase in both CrI and D200 was observed in both the earlywood and latewood of steam-treated wood, ascribing to the greater amount of mesopores in steam-treated wood than CS-treated wood.

Regulated Lignin Structural Units and Soil Organic Carbon Content by Cowpea Peroxidase

<p class="Standard">Peroxidases participate in lignin biosynthesis, but there is no biochemical resolution between the structural units of lignin and soil organic carbon (SOC) contents. Black-eyed beans are staple high-protein foods for millions of at-risk populations in every continent. Its cultivation in semiarid zones could be leveraged to maximize SOC sequestration. Cowpea was treated with stoichiometric mixes of mineral nutrients. Peroxidase was electrophoretically purified from leaves, and assayed for o-dianisidine (guaiacyl units) and pyrogallol (p-hydroxyphenyl units) substrate specificities. Lignin, and SOC compositions were determined by gravimetry. Sulfate-treated cowpea produced the highest lignin (318.88 kg·ha<sup>-1</sup>) because the o-dianisidine maximum velocity (V<sub>max</sub>) value (0.36 µM·min<sup>-1</sup>·mg<sup>-1</sup>) was higher than that for the pyrogallol (0.08 µM·min<sup>-1</sup>·mg<sup>-1</sup>), but the SOC (64.75 kg·ha<sup>-1</sup>) was low due to the guaiacyl being higher than p-hydroxyphenyl units. Peroxidase V<sub>max</sub> value was low (0.12 µM·min<sup>-1</sup>·mg<sup>-1</sup>) for both substrates in the control cowpea, and accordingly lignin (268.44 kg·ha<sup>-1</sup>) and SOC (42.33 kg·ha<sup>-1</sup>) compositions were very low. The pyrogallol V<sub>max</sub> value (0.5 µM·min<sup>-1</sup>·mg<sup>-1</sup>) was lower than the o-dianisidine value (1.0 µM·min<sup>-1</sup>·mg<sup>-1</sup>) for KK-treated cowpea, and accordingly the lignin contents (227.4 kg·ha<sup>-1</sup>) possessed variable compositions of guaiacyl and p-hydroxyphenyl units, leading to very high SOC composition (214.56 kg·ha<sup>-1</sup>). The high SOC sequestration technology involving fertilization with stoichiometric mixes of mineral nutrients could enable limited resource farmers who cultivate cowpeas as cover crop in the Sahel to improve SOM while producing their staple crop.</p>

Composition and structure of an antioxidant acetic acid lignin isolated from shoot shell of bamboo (Dendrocalamus Latiforus)

Bamboo shoot shell (BSS), which contains a large amount of insoluble fibre and lignin, is the main agricultural waste from the production of bamboo shoots. To utilize this waste in a value-added manner, the acetic acid lignin (AL) fraction from BSS was extracted via a combination of hot water pre-treatment and acetic acid post-treatment in the present study. The chemical composition, structural characteristics, and antioxidant activity of AL were investigated and compared to the corresponding milled wood lignin (MWL). The results showed that AL had a higher yield (74%) and lower content of associated carbohydrates (2.96%) than MWL (5.16%). GPC analysis revealed that AL possessed a moderate molecular weight (Mw=2789Da) and narrow polydispersity index (Mw/Mn=1.54). Structural characterization via FT-IR, 1H NMR, 2D-HSQC, and 31P NMR indicated that AL from BSS was a typical HSG-type lignin and was partially acylated at the γ-carbon of the side chain by p-coumarate. Moreover, the bonds between lignin units were predominately β-O-4⿲ linkages. Compared to MWL, AL possessed a characteristically higher phenolic hydroxyl group content and S/G ratio. In terms of the DPPH radical scavenging activity, ABTS radical cation scavenging activity and ferric reducing antioxidant power, AL showed stronger antioxidant activity than MWL and was superior to the commercial synthetic antioxidant BHT. In summary, by applying a modified two-step procedure, which included hot water pre-treatment and acetic acid extraction, AL from BSS was effectively extracted, and the antioxidant potential of AL was characterized.