Isolation and structural characterization of the milled wood lignin, dioxane lignin, and cellulolytic lignin preparations from brewer's spent grain

Hydrothermal depolymerization of different lignins: Insights into structures and reactivities

Hydrothermal depolymerization techniques such as hydrothermal liquefaction (HTL) are promising methods for converting biomass into fuel and valuable chemicals. While the HTL of lignin has been extensively studied, its fundamental chemistry remains underexplored, particularly regarding the reactivity differences among various major technical lignins under HTL conditions. A deeper understanding of these variations is essential for optimizing HTL processes. In this report, four major types of technical lignins-dioxane lignin, Kraft lignin, ethanosolv lignin, and soda lignin-extracted from the same pine sawdust were thoroughly characterized and subjected to neutral or base-catalyzed HTL at 330 °C for 1 h. The bio-oils derived from these lignins were analyzed for their physical and chemical properties. The data indicate that, while the structural differences between the lignins influenced the HTL outcomes, their impact was significantly smaller compared to the effect of the presence of a catalyst. To better understand the relationship between lignin structure and the resulting monomeric products, model compounds representing key structural motifs in technical lignins (namely β-O-4, styryl ether, and phenyl glycerol) were synthesized and tested under HTL conditions to simulate the lignin depolymerization process. Additionally, computational methods were employed to elucidate its reaction pathways.

Tunning antisolvent precipitation for the synthesis of lignin nanoparticles using lignin extracted from different agro-industrial wastes

Lignin nanoparticles (LNPs) show great potential in UV-protectants, drugs carriers, encapsulation, supercapacitors, and others. This study proposes the development of an optimised LNP synthesis method by antisolvent precipitation, using lignin from persimmon tree pruning waste, green coconut waste, and sugarcane bagasse. The best synthesis conditions were determined evaluating the chemical composition and the physicochemical properties of the LNPs, by varying the antisolvent addition rate, initial lignin concentration and antisolvent pH. Optimal precipitation conditions - 250 μL·s-1, 5 mg·mL-1 of lignin, pH 7.0 (antisolvent), 250 μL·s-1 adding antisolvent - converted the persimmon, coconut, and the sugarcane lignin into nanometric structures (Ø = 130-192 nm), with a spherical morphology, which were stable during storage at 5 °C for 90 days. Particle formation did not cause significant changes in the chemical composition of the lignins, and regardless of the plant origin, the LNPs showed higher UV absorption and thermal stability than the original corresponding lignins.

Structural features of dioxane lignin: A comparative study with milled wood and formaldehyde-stabilized lignins

Dioxane lignin (DL) is isolated from plant material under mild acidolysis conditions and is widely used in many studies as a representative sample of protolignin, an alternative to milled wood lignin (MWL). However, the structural changes caused by hydrolytic degradation reactions during DL extraction are still poorly understood. In this work, an integrated approach based on 2D NMR and high-resolution mass spectrometry was used to establish the features of the lignin structure on the example of pine lignin isolated using dioxane under various conditions: MWL, DL and "formaldehyde stabilized" lignin (LSF). In this context, we sought to gain a deeper understanding of the chemical structure of DL, focusing on the least studied fragments. Cross-peaks related to the degradation products of 1,2-diarylpropane were uniquely identified for the first time by a combination of HSQC-HMBC spectra. In addition, the 1,3-dioxane structure of β-aryl ether, the presence of which in DL has not been previously observed and originates from elements of the native structure and formaldehyde (product of lignin destruction), was unambiguously shown and confirmed by NMR and mass spectrometry analysis. Additionally, signals related to the 1,3-dioxane structure of 1,2-diarylpropane were also detected for the first time in the HSQC spectrum of LSF.

Study on structural alterations and degradation mechanism of lignin from ozone treated scutched flax tow (SFT)

Ozone is commonly used in lignocellulosic fiber extraction and degumming processes because of its selective reactivity with lignin. However, most studies have focused on the removal of non-cellulosic substances from various lignocellulosic fibers (e.g., wood, pulp, bamboo, and sugarcane bagasse) and the conversion and utilization of the obtained lignin. The lignin degradation mechanism in lignocellulosic fibers during ozone degumming/extraction remains poorly understood. In this study, the structural alterations of milled wood lignin (MWL) isolated from scutched flax tow (SFT) before and after ozone treatment were examined using Fourier transform infrared spectroscopy (FTIR), ultraviolet spectroscopy (UV), gel permeation chromatography (GPC), elemental analysis, thermogravimetric analysis (TGA), pyrolysis-gas chromatography-mass spectroscopy (Py-GC/MS) and nuclear magnetic resonance spectroscopy (NMR). The results showed that the MWL from SFT was primarily composed of syringyl (S) and guaiacyl (G) units. 2D HSQC NMR results revealed that the β-O-4' linkages were dominant in the lignin of SFT. After ozone treatment, some of β-O-4' and β-β linkages and most of β-5 linkages were damaged. The S-type units further degraded into G-type units in ozone treatment system. Overall, this work provides a detailed analysis and valuable insights into the delignification mechanism of the widely used ozone degumming/extraction process for lignocellulose fibers.

Characteristic study of Candida rugosa lipase immobilized on lignocellulosic wastes: effect of support material

For the first time is reported the comparison of solid biocatalysts derived from Candida rugosa lipase (CRL) immobilized on different lignocellulosic wastes (rice husk, brewer's spent grain, hemp tea waste, green tea waste, vine bark, and spent coffee grounds) focusing on the characterization of these materials and their impact on the lipase-support interaction. The wastes were subjected to meticulous characterization by ATR-FTIR, BET, and SEM analysis, besides lignin content and hydrophobicity determination. Investigating parameters influencing immobilization performance revealed the importance of morphology, textural properties, and hydrophobic interactions revealed the importance of morphology, textural properties and especially hydrophobic interactions which resulted in positive correlations between surface hydrophobicity and lipase immobilization efficiency. Hemp tea waste and spent coffee grounds demonstrated superior immobilization performances (7.20 U/g and 8.74 U/g immobilized activity, 102.3% and 33.5% efficiency, 13.4% and 15.4% recovery, respectively). Moreover, they demonstrated good temporal stability (100% and 92% residual activity after 120 days, respectively) and retained 100% of their immobilized activity after five reuses in the hydrolysis of p-nitrophenyl palmitate in hexane. In addition, the study of enzymatic desorption caused by ionic strength and detergent treatments indicated mixed hydrophobic and electrostatic interactions in rice husk, vine bark, and spent coffee grounds supports, while hemp tea waste and green tea waste were dominated by hydrophobic interactions.

Polymeric phenylpropanoid derivatives crosslinked by hydroxyl fatty acids form the core structure of rape sporopollenin

Sporopollenin, a critical innovation in the evolution of terrestrial plants, is the core building brick for the outer wall of land-plant spores and pollen. Despite its significance, the basic structure of sporopollenin remains elusive due to its extreme chemical inertness. In this study, we used ethanolamine to completely dissolve rape sporopollenin and successfully identified a total of 22 components, including fatty acids, p-coumaric acid, sterols and polymeric phenylpropanoid derivatives. After that, using NaOH treatment and partial dissolution, alongside Arabidopsis mutants analysis and spectroscopic methods, we determined that polymeric phenylpropanoid derivatives crosslinked by hydroxyl fatty acids serve as the core structure of sporopollenin. The free hydroxyl groups and carboxyl groups of the polymeric phenylpropanoid derivatives can be modified by other fatty acids (C16:0, C18:0 and C18:3) as well as alcohols/phenols (for example, naringenin, β-sitosterol), resulting in a structure that protects pollen from terrestrial stresses. This discovery provides a basis for further exploration of sporopollenin's role in plant reproduction and evolution.

Isolation and Structural Characterization of Natural Deep Eutectic Solvent Lignin from Brewer's Spent Grains

Brewer's spent grains (BSG) offer valuable opportunities for valorization beyond its conventional use as animal feed. Among its components, lignin-a natural polymer with inherent antioxidant properties-holds significant industrial potential. This work investigates the use of microwave-assisted extraction combined with acidic natural deep eutectic solvents (NaDESs) for efficient lignin recovery, evaluating three different NaDES formulations. The results indicate that choline chloride-lactic acid (ChCl-LA), a NaDES with superior thermal stability as confirmed via thermogravimetric analysis (TGA), is an ideal solvent for lignin extraction at 150 °C and 15 min, achieving a balance of high yield and quality. ChCl-LA also demonstrated good solubility and cell disruption capabilities, while microwaves significantly reduced processing time and severity. Under optimal conditions, i.e., 150 °C, 15 min, in the presence of ChCl-LA NaDES, the extracted lignin achieved a purity of up to 79% and demonstrated an IC50 (inhibitory concentration 50%) of approximately 0.022 mg/L, indicating a relatively strong antioxidant activity. Fourier transform infrared (FTIR) and 2D-HSQC NMR (heteronuclear single quantum coherence nuclear magnetic resonance) spectroscopy confirmed the successful isolation and preservation of its structural integrity. This study highlights the potential of BSG as a valuable lignocellulosic resource and underscores the effectiveness of acidic NaDESs combined with microwave extraction for lignin recovery.

Tritordeum, a hybrid cereal with a highly tricin-enriched lignin

The lignin from tritordeum straw, a hybrid cereal from crossbreeding of durum wheat and wild barley, was isolated and chemically characterized. Its composition and structure were studied by analytical pyrolysis (Py-GC/MS), nuclear magnetic resonance spectroscopy (NMR), Derivatization Followed by Reductive Cleavage (DFRC) method, and gel permeation chromatography (GPC). The data revealed an enrichment of guaiacyl (G) units (H:G:S of 3:61:36), which had a significant impact on the distribution of inter-unit linkages. The predominant linkages were the β-O-4' alkyl-aryl ethers (78 % of all linkages), with substantial proportions of condensed linkages such as phenylcoumarans (11 %), resinols (4 %), spirodienones (4 %), and dibenzodioxocins (2 %). Moreover, DFRC revealed that tridordeum straw lignin was partly acylated at the γ-OH with both acetates and p-coumarates. Acetates were principally attached to G-units, whereas p-coumarates were predominantly attached to S-units. Furthermore, and more importantly, tritordeum lignin incorporates remarkable amounts of a valuable flavone, tricin, exceeding 30 g per kilogram of straw. Given the diverse industrial applications associated with this high-value molecule, tritordeum straw emerges as a promising and sustainable resource for its extraction.

Capacity of Aqueous Solutions of the Ionic Liquid 1-Ethyl-3-methylimidazolium Acetate to Partially Depolymerize Lignin at Ambient Temperature and Pressure

Lignin is a very attractive and abundant biopolymer with the potential to be a biorenewable source of a large number of value-added organic chemicals. The current state-of-the-art methods fail to provide efficient valorization of lignin in this regard without the involvement of harsh conditions and auxiliary substances that compromise the overall sustainability of the proposed processes. Making an original approach from the set of mildest temperature and pressure conditions, this work identifies and explores the capacity of an aqueous solution of the nonvolatile ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) to partially depolymerize technical lignin (Indulin AT) by means of a treatment consisting in the simple contact at ambient temperature and pressure. Among a considerable number of valuable phenolic molecules that were identified in the resulting fluid, vanillin (yield of about 3 g/kg) and guaiacol (yield of about 1 g/kg) were the monophenolic compounds obtained in a higher concentration. The properties of the post-treatment solids recovered remain similar to those of the original lignin, although with a relatively lower abundance of guaiacyl units (in agreement with the generation of guaiacyl-derived phenolic molecules, such as vanillin and guaiacol). The assistance of the treatment with UV irradiation in the presence of nanoparticle catalysts does not lead to an improvement in the yields of phenolic compounds.

Lignin, the Lignification Process, and Advanced, Lignin-Based Materials

At a time when environmental considerations are increasingly pushing for the application of circular economy concepts in materials science, lignin stands out as an under-used but promising and environmentally benign building block. This review focuses (A) on understanding what we mean with lignin, i.e., where it can be found and how it is produced in plants, devoting particular attention to the identity of lignols (including ferulates that are instrumental for integrating lignin with cell wall polysaccharides) and to the details of their coupling reactions and (B) on providing an overview how lignin can actually be employed as a component of materials in healthcare and energy applications, finally paying specific attention to the use of lignin in the development of organic shape-memory materials.

Relationship between the Change in E/T Ratio and the Cooking Performance of Eucalyptus and Acacia Woods during Kraft Pulping Process

Lignin structure is an important factor affecting the cooking part of the pulping process. In this study, the effect of lignin side chain spatial configuration on cooking performance was analyzed, and the structural characteristics of eucalyptus and acacia during cooking were compared and studied by combining ozonation, GC-MS, NBO, and 2D NMR (¹H-¹³C HSQC). In addition, the changes in the lignin content of four different raw materials during the cooking process were studied via ball milling and UV spectrum analysis. The results showed that the content of lignin in the raw material decreased continuously during the cooking process. Only in the late cooking stage, when the lignin removal reached its limit, did the lignin content tend to be stable due to the polycondensation reaction of lignin. At the same time, the E/T ratio and S/G ratio of the reaction residual lignin also followed a similar rule. At the beginning of cooking, the values of E/T and S/G decreased rapidly and then gradually rose when they reached a low point. The different initial E/T and S/G values of different raw materials lead to the disunity of cooking efficiency and the different transformation rules of different raw materials in the cooking process. Therefore, the pulping efficiency of different raw materials can be improved using different technological means.

How does maturity stage affect seeds metabolome via UPLC/MS based molecular networking and chemometrics and in relation to antioxidant effect? A case study in 4 major cereals and legumes

Legumes and cereals as staple food are typically consumed at mature stage, though also consumed at earlier stages. UPLC/MS based molecular networking and chemometrics were employed for the first time to address metabolome composition heterogeneity amongst seeds in the context of their maturity stages. The study included 4 major cereal and leguminous seeds of different species, and cultivars i.e., Triticum aestivum, Hordeum vulgare, Vicia faba and Cicer arietinum. 146 Metabolites from various classes were identified of which several are first time to be reported. Supervised OPLS model of all datasets revealed that sugars and oxylipids were dominant in mature and immature seeds, respectively. DPPH and FRAP assays were assessed for differential secondary metabolites' correlation. Results were attributed to flavonoids, oxylipids, and amino acids/peptides. Mature barley seeds possessed the strongest antioxidant activity among examined seeds. This study provides novel insights on seeds' maturation process in context to holistic metabolic changes.

Dynamic structural evolution of lignin macromolecules and hemicelluloses during Chinese pine growth

To comprehend the biosynthesis processes of conifers, it is essential to investigate the disparity between the cell wall shape and the interior chemical structures of polymers throughout the development of Chinese pine. In this study, branches of mature Chinese pine were separated according to their growth time (2, 4, 6, 8 and 10 years). The variation of cell wall morphology and lignin distribution was comprehensively monitored by scanning electron microscopy (SEM) and confocal Raman microscopy (CRM), respectively. Moreover, the chemical structures of lignin and alkali-extracted hemicelluloses were extensively characterized by nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The thickness of latewood cell walls increased steadily from 1.29 μm to 3.38 μm, and the structure of the cell wall components became more complicated as the growth time increased. Based on the structural analysis, it was found that the content of β-O-4 (39.88-45.44/100 Ar), β-β (3.20-10.02/100 Ar) and β-5 (8.09-15.35/100 Ar) linkages as well as the degree of polymerization of lignin increased with the growth time. The complication propensity increased significantly over 6 years before slowing to a trickle over 8 and 10 years. Furthermore, alkali-extracted hemicelluloses of Chinese pine mainly consist of galactoglucomannans and arabinoglucuronxylan, in which the relative content of galactoglucomannans increased with the growth of the pine, especially from 6 to 10 years.

Ultrastructural elucidation of lignin macromolecule from different growth stages of Chinese pine

Understanding of the morphological changes at different growth stages and lignin accumulation pattern for pine biomass plays the key role in facilitating the further development of value-added utilization and downstream conversion processes. This work systematically revealed the morphological change and lignin accumulation pattern in Chinese pine branches cell walls via confocal Raman microscopy (CRM) technology. Meanwhile, the structural characteristics of isolated lignin samples from different growth stages were synthetically characterized by nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) techniques. The results indicated that the content of pith in adult pine new branch was bigger than juvenile trees. With the increase of physiological age, the branches in adult pine could accumulate more lignin both in overall content and the concentration of cell corner middle layer. Moreover, the significantly increases of molecular weights and the β-O-4, β-β linkages content revealed that the lignin macromolecule of pine would polymerize faster in the adult stage (14, 35 years). The panorama generated from the structural and chemical features of pine native lignin not only benefited to understand the biosynthetic pathways and lignin macromolecules structural variation in plant cell walls from different growth stages but also contributed to the valorization and deconstruction of biomass.

Effect of Ternary Deep Eutectic Solvents on Bagasse Cellulose and Lignin Structure in Low-Temperature Pretreatment

Deep eutectic solvents (DESs) have been used for the pretreatment of lignocellulose and showed selective dissolution for different lignocellulosic components. In this study, six new ternary DESs were synthesized on the basis of anhydrous oxalic acid DES by adding alcohol, acid, and deionized water, respectively, including choline chloride/anhydrous oxalic acid/ethylene glycol (ChCl-OA-EG), choline chloride/anhydrous oxalic acid/glycerol (ChCl-OA-G), choline chloride/anhydrous oxalic acid/lactic acid (ChCl-OA-LA), choline chloride/anhydrous oxalic acid/malonic acid (ChCl-OA-MA), choline chloride/anhydrous oxalic acid/10% H2O (v/v) (ChCl-OA + 10% H2O), and choline chloride/anhydrous oxalic acid/20% H2O (v/v) (ChCl-OA + 20% H2O). The lignin in bagasse was extracted and separated with these ternary DESs, and Fourier Transform Infrared (FTIR), Scanning electron microscope (SEM), X-ray diffraction (XRD), Two-dimensional Heteronuclear Single Quantum Coherence (2D HSQC), and Thermogravimetric analysis (TG) were used to characterize the molecular structures of lignin and cellulose. The results showed that under the mild reaction condition of cooking at 90 °C for 4 h, all six ternary DESs effectively dissolved hemicellulose in bagasse, the DES ChCl-OA-MA prepared with malonic acid significantly increased the removal of lignin (71.64%) by breaking the β-O-4′ ether bond of lignin molecules, and the crystallinity of cellulose was also significantly improved (67.65%).

Towards a Complete Exploitation of Brewers’ Spent Grain from a Circular Economy Perspective

In the present work, brewers’ spent grain (BSG), which represents the major by-product of the brewing industry, was recovered from a regional brewery and fractionated in order to obtain a complete valorization. In particular, the whole process was divided in two main parts. A first pretreatment with hot water in an autoclave allowed the separation of a solution containing the soluble proteins and sugars, which accounted for 25% of the total starting biomass. This first step allowed the preparation of a medium that was successfully employed as a valuable growing medium for different microbial fermentations, leading to valuable fungal biomass as well as triglycerides with a high content of linear or branched fatty acids, depending on the microorganism used. The solid water-insoluble residue was then submitted to a lignocellulose deep eutectic solvent-mediated fractionation, which allowed the recovery of two important main fractions: BSG cellulose and BSG lignin. The latter product was tested as potential precursor for the development of cement water reducers with encouraging results. This combination of treatments of the waste biomass appeared to be a promising sustainable strategy for the development of the full exploitation of BSG from a circular economy perspective.

How water-soluble saccharides drive the metabolism of lactic acid bacteria during fermentation of brewers' spent grain

We proposed a novel phenomic approach to track the effect of short-term exposures of Lactiplantibacillus plantarum and Leuconostoc pseudomesenteroides to environmental pressure induced by brewers' spent grain (BSG)-derived saccharides. Water-soluble BSG-based medium (WS-BSG) was chosen as model system. The environmental pressure exerted by WS-BSG shifted the phenotypes of bacteria in species- and strains-dependent way. The metabolic drift was growth phase-dependent and likely underlay the diauxic profile of organic acids production by bacteria in response to the low availability of energy sources. Among pentosans, metabolism of arabinose was preferred by L. plantarum and xylose by Leuc. pseudomesenteroides as confirmed by the overexpression of related genes. Bayesian variance analysis showed that phenotype switching towards galactose metabolism suffered the greatest fluctuation in L. plantarum. All lactic acid bacteria strains utilized more intensively sucrose and its plant-derived isomers. Sucrose-6-phosphate activity in Leuc. pseudomesenteroides likely mediated the increased consumption of raffinose. The increased levels of some phenolic compounds suggested the involvement of 6-phospho-β-glucosidases in β-glucosides degradation. Expression of genes encoding β-glucoside/cellobiose-specific EII complexes and phenotyping highlighted an increased metabolism for cellobiose. Our reconstructed metabolic network will improve the understanding of how lactic acid bacteria may transform BSG into suitable food ingredients.

Monitoring transformation of two tropical lignocellulosics and their lignins after residence in Benin soils

Thermally assisted Hydrolysis and Methylation (THM), and 2D-heteronuclear single quantum coherence nuclear magnetic resonance (2D HSQC NMR) spectroscopy were used to monitor the transformation of ramial chipped wood (RCW) from Gmelina arborea and Sarcocephalus latifolius, together with their organosolv lignins, following soil incubation in Benin (West Africa). Mesh litterbags containing RCW were buried in soils (10 cm depth) and were retrieved after 0, 6, 12 and 18 months of field incubation. Chemical analysis showed that total carbohydrate content decreased, while total lignin content increased as RCW decomposition progressed. Ash and mineral content of RCW increased significantly after 18 months of decomposition in soil. Significant N-enrichment of the RCW was determined following 18 months incubation in soils, reaching 2.6 and 1.9 times the initial N-content for G. arborea and S. latifolius. Results of THM showed that the S + G sum, corresponding to lignins, increased with RCW residence time in the soils, in contrast to the response of compounds derived from carbohydrates, the sum of which decreased. Remarkably, lignin interunit linkages, most notably β-O-4' aryl ethers, β-β' resinol, β-5' phenylcoumaran and p-PCA p-coumarate, survived after 18 months in the soil, despite their gradual decrease over the duration of the experiment.

New Insights on Structures Forming the Lignin-Like Fractions of Ancestral Plants

In the present work, lignin-like fractions were isolated from several ancestral plants -including moss (Hypnum cupressiforme and Polytrichum commune), lycophyte (Selaginella kraussiana), horsetail (Equisetum palustre), fern (Nephrolepis cordifolia and Pteridium aquilinum), cycad (Cycas revoluta), and gnetophyte (Ephedra fragilis) species- and structurally characterized by pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) and two-dimensional nuclear magnetic resonance (2D-NMR) spectroscopy. Py-GC/MS yielded marker compounds characteristic of lignin units, except in the H. cupressiforme, P. commune and E. palustre "lignins," where they were practically absent. Additional structural information on the other five samples was obtained from 2D-NMR experiments displaying intense correlations signals of guaiacyl (G) units in the fern and cycad lignins, along with smaller amounts of p-hydroxyphenyl (H) units. Interestingly, the lignins from the lycophyte S. kraussiana and the gnetophyte E. fragilis were not only composed of G- and H-lignin units but they also incorporated significant amounts of the syringyl (S) units characteristic of angiosperms, which appeared much later in plant evolution, most probably due to convergent evolution. The latter finding is also supported by the abundance of syringol derivatives after the Py-GC/MS analyses of these two samples. Regarding lignin structure, β-O-4' alkyl-aryl ethers were the most abundant substructures, followed by condensed β-5' phenylcoumarans and β-β' resinols (and dibenzodioxocins in the fern and cycad lignins). The highest percentages of alkyl-aryl ether structures correlated with the higher S/G ratio in the S. Kraussiana and E. fragilis lignin-like fractions. More interestingly, apart from the typical monolignol-derived lignin units (H, G and S), other structures, assigned to flavonoid compounds never reported before in natural lignins (such as amentoflavone, apigenin, hypnogenol B, kaempferol, and naringenin), could also be identified in the HSQC spectra of all the lignin-like fractions analyzed. With this purpose, in vitro synthesized coniferyl-naringenin and coniferyl-apigenin dehydrogenation polymers were used as standards. These flavonoids were abundant in H. cupressiforme appearing as the only constituents of the moss lignin-like fraction (including 84% of dimeric hypnogenol B) and their abundance decreased in those of S. Kraussiana (with amentoflavone and naringenin representing 14% of the total aromatic units), and the two ancient gymnosperms (0.4-1.2%) and ferns (0-0.7%).

Structural Characteristics of the Guaiacyl-Rich Lignins From Rice (Oryza sativa L.) Husks and Straw

Rice (Oryza sativa L.) is a major cereal crop used for human nutrition worldwide. Harvesting and processing of rice generates huge amounts of lignocellulosic by-products such as rice husks and straw, which present important lignin contents that can be used to produce chemicals and materials. In this work, the structural characteristics of the lignins from rice husks and straw have been studied in detail. For this, whole cell walls of rice husks and straw and their isolated lignin preparations were thoroughly analyzed by an array of analytical techniques, including pyrolysis coupled to gas chromatography-mass spectrometry (Py-GC/MS), nuclear magnetic resonance (NMR), and derivatization followed by reductive cleavage (DFRC). The analyses revealed that both lignins, particularly the lignin from rice husks, were highly enriched in guaiacyl (G) units, and depleted in p-hydroxyphenyl (H) and syringyl (S) units, with H:G:S compositions of 7:81:12 (for rice husks) and 5:71:24 (for rice straw). These compositions were reflected in the relative abundances of the different interunit linkages. Hence, the lignin from rice husks were depleted in β-O-4' alkyl-aryl ether units (representing 65% of all inter-unit linkages), but presented important amounts of β-5' (phenylcoumarans, 23%) and other condensed units. On the other hand, the lignin from rice straw presented higher levels of β-O-4' alkyl-aryl ethers (78%) but lower levels of phenylcoumarans (β-5', 12%) and other condensed linkages, consistent with a lignin with a slightly higher S/G ratio. In addition, both lignins were partially acylated at the γ-OH of the side-chain (ca. 10-12% acylation degree) with p-coumarates, which overwhelmingly occurred over S-units. Finally, important amounts of the flavone tricin were also found incorporated into these lignins, being particularly abundant in the lignin of rice straw.

Role of Lactic Acid Bacteria Phospho-β-Glucosidases during the Fermentation of Cereal by-Products

Bioprocessing using lactic acid bacteria (LAB) is a powerful means to exploit plant-derived by-products as a food ingredient. LAB have the capability to metabolize a large variety of carbohydrates, but such metabolism only relies on few metabolic routes, conferring on them a high fermentation potential. One example of these pathways is that involving phospho-β-glucosidase genes, which are present in high redundancy within LAB genomes. This enzymatic activity undertakes an ambivalent role during fermentation of plant-based foods related to the release of a wide range of phenolic compounds, from their β-D-glycosylated precursors and the degradation of β-glucopyranosyl derived carbohydrates. We proposed a novel phenomic approach to characterize the metabolism drift of Lactiplantibacillus plantarum and Leuconostoc pseudomesenteroides caused by a lignocellulosic by-product, such as the brewers’ spent grain (BSG), in contrast to Rich De Man, Rogosa and Sharpe (MRS) broth. We observed an increased metabolic activity for gentiobiose, cellobiose and β-glucoside conjugates of phenolic compounds during BSG fermentation. Gene expression analysis confirmed the importance of cellobiose metabolism while a release of lignin-derived aglycones was found during BSG fermentation. We provided a comprehensive view of the important role exerted by LAB 6-phospho-β-glucosidases as well the major metabolic routes undertaken during plant-based fermentations. Further challenges will consider a controlled characterization of pbg gene expression correlated to the metabolism of β-glucosides with different aglycone moieties.

Mild Acetylation and Solubilization of Ground Whole Plant Cell Walls in EmimAc: A Method for Solution-State NMR in DMSO-d6

Lignocellulosic biomass is mainly composed of polysaccharides and lignin. The complexity and diversity of the plant cell wall polymers makes it difficult to isolate the components in pure form for characterization. Many current approaches to analyzing the structure of lignocellulose, which involve sequential extraction and characterization of the resulting fractions, are time-consuming and labor-intensive. The present study describes a new and facile system for rationally derivatizing and dissolving coarsely ground plant cell wall materials. Using ionic liquids (EmimAc) and dichloroacetyl chloride as a solvent/reagent produced mildly acetylated whole cell walls without significant degradation. The acetylated products were soluble in DMSO-d₆ from which they can be characterized by solution-state two-dimensional nuclear magnetic resonance (2D NMR) spectrometry. A distinct advantage of the procedure is that it realizes the dissolution of whole lignocellulosic materials without requiring harsh ball milling, thereby allowing the acquisition of high-resolution 2D NMR spectra to revealing structural details of the main components (lignin and polysaccharides). The method is therefore beneficial to understanding the composition and structure of biomass aimed at its improved utilization.

Color evolution of poplar wood chips and its response to lignin and extractives changes in autohydrolysis pretreatment

Combining chemi-mechanical pulping with autohydrolysis pretreatment is an efficient and value-added utilization approach for lignocellulosic biomass in paper industry. To further promote the utilization of autohydrolyzed biomass in chemi-mechanical pulping, the color evolution of poplar wood chips in autohydrolysis pretreatment and its chromogenic mechanism were investigated by using CIELab color system, FT-IR, NMR and GPC. The results showed that the total color difference ΔE* increased obviously, which were remarkable as the combined hydrolysis factor (CHF) increased. The lignin content led to a more significant influence on the color of poplar wood chips than the extractives. The autohydrolysis pretreatment with a higher CHF accelerated the degradation and subsequent condensation of lignin, resulting in the formation of chromophoric groups, such as Hibbert ketone, quinones and quinone methides. It is of great significance for biomass refinery and paper industry to reveal the color evolution of poplar wood chips caused by autohydrolysis pretreatment from the point of view of chemical components' structure.

pH-Responsive Lignin-Based Nanomicelles for Oral Drug Delivery

A pH-stimuli amphiphilic lignin-based copolymer was prepared, and it could self-assemble to form spherical nanomicelles with the addition of "switching" water. The morphology, structure, and physical properties of micelles were characterized with transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), particle-size analysis, and zeta-potential measurement. In vitro drug release exemplified that the micelles were pH-sensitive, retaining more than 84.36% ibuprofen (IBU) in simulated gastric fluid (pH 1.5) and presenting a smooth release of 81.81% IBU in simulated intestinal fluid (pH 7.4) within 72 h. Cell culture studies showed that the nanomicelles were biocompatible and boosted the proliferation of human bone marrow stromal cells hBMSC and mouse embryonic fibroblast cells NIH-3T3. Interestingly, the nanomicelles inhibited the survival of human colon cancer cells HT-29 with a final survival rate of only 5.34%. Therefore, this work suggests a novel strategy to synthesize intelligent lignin-based nanomicelles that show a great potential as oral drug carriers.

Dataset on structure-antioxidant activity relationship of active oxygen catalytic lignin and lignin-carbohydrate complex

The data presented in this article are related to the research article entitled “Structure-antioxidant activity relationship of active oxygen catalytic lignin and lignin-carbohydrate complex” (Jiang et al.). It supplements the article with thermostability of milled wood lignin (MWL) and alkali-oxygen lignin (AOL), main substructures of lignin in rice straw, main products and yield of nitrobenzene oxidation of lignin-carbohydrate complexes (LCCs), Fourier transform infrared spectroscopy of LCCs, radical (ABTS·) scavenging ability of lignins and signal assignment of lignins and LCCs in nuclear magnetic resonance spectra (¹H, ¹³C, 2D HSQC NMR). The dataset is made publicly available and can be useful for extending the structural and bioactive research and critical analyses of lignin and LCC.

Lignin and Cellulose Blends as Pharmaceutical Excipient for Tablet Manufacturing via Direct Compression

Extensive efforts are being made to find alternative uses for lignin (LIG). In the present work the use of this biopolymer as excipient to prepare tablets was studied. For this purpose, LIG was combined with microcrystalline cellulose (MCC) and used as excipients to prepare directly compressed tablets containing a model drug, tetracycline (TC). The excipients contained different concentrations of LIG: 100%, 75%, 50%, 25% and 0% (w/w). Two different compression forces were used (two and five tonnes). When formulations were prepared using LIG as the only excipient, tablets were formed, but they showed lower densities and crushing strength than the ones obtained with only MCC or LIG/MCC blends. Moreover, tablets prepared using five tonnes of compression force showed TC releases ranging from 40% to 70% of the drug loading. On the other hand, the tablets prepared using two tonnes of compression force showed a faster and more efficient TC release, between 60% and 90%. The presence of LIG in the tablets modified significantly the release profile and the maximum amount of TC released. Finally, a DPPH (2,2-diphenyl-1-picrylhydrozyl) assay was performed to confirm that the presence of LIG provided antioxidant properties to the formulations. Accordingly, LIG has potential as a pharmaceutical excipient.

Ethanol/1,4-dioxane/formic acid as synergistic solvents for the conversion of lignin into high-value added phenolic monomers

In this study, a mixture solvent of ethanol/1,4-dioxane/formic acid (FA) is firstly reported to efficaciously depolymerize industrial lignin to produce high-value added phenolic monomers, in which 1,4-dioxane acts as lignin solvent, ethanol acts as solvent, reactant and in situ hydrogen donor, and FA acts as acid catalyst and in situ hydrogen donor. The effects of solvent composition and reaction conditions on the lignin conversion and product yields were explored, resulting in a low residue yield of 6.57% and a high phenolic monomers yield of 22.4% at 300 °C for 2 h when Kraft lignin was depolymerized in the mixture solvent of ethanol/1,4-dioxane/FA (10:10:2, v/v). Moreover, possible reaction mechanism on lignin depolymerization in the mixture solvent was illustrated, suggesting a favorable synergistic effect among the three components of the mixture solvent. In addition, the satisfactory applicability of the mixture solvent was approved through the feedstock adaptability and recyclability experiments.

Effects of synergistic fungal pretreatment on structure and thermal properties of lignin from corncob

Synergistic fungal pretreatment involving white-rot and brown-rot fugal pretreatment has shown great potential for enhancing the yield of sugars from biomass time-effectively and environmentally benign. In this work, the effects of this integrated fungal pretreatment on lignin characteristics and thermal behavior of corncob were examined in the view of whole plant valorization. The results show that an efficient deconstruction of lignin was achieved by white-rot fungus, and subsequent brown-rot fungus promoted the preferential breakdown of guaiacyl units, further enhancing lignin extraction efficiency (62.3%). Consequently, less phenolic hydroxyl, methoxyl, tricin, ester-linked p-coumaric acid, more carboxylic acid, ratio of syringyl to guaiacyl units, β-O-4' linkage and molecular weight were found in W-BL. Thermal stability was improved and the increased phenol and alkyl-phenols contents in pyrolysis products demonstrated that synergistic fungal pretreatment definitely improved the lignin oil quality. These discoveries provide new insights into set strategy for microbial screening, pretreatment and lignin processing.

Structural Characterization of Lignin in Four Cacti Wood: Implications of Lignification in the Growth Form and Succulence

Wood lignin composition strongly depends on anatomical features and it has been used as a marker for characterizing major plant groups. Wood heterogeneity in Cactaceae is involved in evolutionary and adaptive processes within this group; moreover, it is highly correlated to the species growth form. Here we studied the lignin structure from different types of woods in four Cactaceae species with different stem morphologies (Pereskia lychnidiflora, tree/fibrous wood; Opuntia streptacantha and Pilosocereus chrysacanthus, tree/succulent fibrous wood; Ferocactus hamatacanthus, cylindrical stem/dimorphic wood) in order to determine their relationship with the wood anatomy in an evolutionary-adaptive context. Dioxane lignin was isolated and analyzed by pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS), two-dimensional nuclear magnetic resonance spectroscopy (2D-NMR) and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The main linkages are the β-O-4' ether (67-85%), the β-β' resinol (10-26%) and the β-5' and α-O-4' linkages of the phenylcoumaran structures (≤7%). Spirodienone structures have a considerable abundance (5%) in the dimorphic wood of F. hamatacanthus. In addition, low contents (≤3%) of α,β-diaryl ether, α-oxidized β-O-4' ether and dibenzodioxocin structures were found. The sinapyl- and coniferyl acetates are not part of the wood lignin in any of the studied species. The low (≤5%) γ-acetylation in the F. hamatacanthus and P. chrysacanthus wood lignin is here interpreted as an evidence of a high specialization of the wood elements in the conduction/storage of water. The lignin of the studied Cactaceae is composed predominantly of guaiacyl and syringyl units (S/G: 0.9-16.4). High abundance of syringyl units (62-94%) in three of the four species is considered as a defense mechanism against oxidative agents, it is a very conspicuous trait in the most succulent species with dimorphic wood. Furthermore, it is also associated with ferulates and the herein called γ-acetylated guaiacyl-syringaresinol complexes acting as nucleation sites for lignification and as cross-links between lignin and carbohydrates at the wide-band tracheid-fiber junctions.

Relevance between chemical structure and pyrolysis behavior of palm kernel shell lignin

Palm kernel shell (PKS) lignin obtained by enzymatic/mild acid hydrolysis (EMAL) was thoroughly elucidated by FTIR (fourier transform infrared), ¹³C-¹H 2D-NMR (nuclear magnetic resonance), quantitative ³¹P NMR combined with DFRC (derivatization followed by reductive cleavage), and Py-GC/MS (pyrolysis-gas chromatography/mass spectrometry) with and without TMAH (tetramethylammonium hydroxide). Pyrolysis behavior was then characterized by TG-FTIR-MS (thermo-gravimetric-FTIR-mass spectrometry) and Py-GC/MS. The PKS lignin is demonstrated to be a p-hydroxyphenyl-guaiacyl-syringyl (H-G-S) lignin with abundances of p-hydrobenzoates and low S/G ratio of 0.15. 2D-NMR indicated that the main substructures are β-O-4-ethers (~85%), and ³¹P NMR/DFRC quantified the total β-O-4 content of 2295μmol/g. Py-GC/MS with and without TMAH confirmed that phenol mainly originated from p-hydroxybenzoates units. Thermal-stability, evolution behavior of typical volatiles, and selectivity of phenolic compounds (H-, G-, S-, C-type) during PKS lignin pyrolysis were explored. Relationship between chemical structure and pyrolysis behavior are also obtained. This work will provide a deep insight to the effective utilization of PKS.

Elucidating Tricin-Lignin Structures: Assigning Correlations in HSQC Spectra of Monocot Lignins

Tricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one] is a flavone that has been found to be incorporated in grass lignin polymers via 4'⁻O⁻β coupling. Herein, we investigated the tricin-lignin structure using nuclear magnetic resonance (NMR) methods by comparing the 1H⁻13C heteronuclear correlation (HSQC) NMR spectra of the isolated lignin with a series of dimeric and trimeric tricin-4'⁻O⁻β-ether model compounds. Results showed that the tricin moiety significantly affects the chemical shift of the Cβ/Hβ of 4'⁻O⁻β unit, producing peaks at around δC/δH 82.5⁻83.5/4.15⁻4.45, that differ from the Cβ/Hβ correlations from normal 4⁻O⁻β units formed solely by monolignols, and that have to date been unassigned.

Structural characterization of Chinese quince fruit lignin pretreated with enzymatic hydrolysis

Lignin is an increasingly valuable raw material for industrial, pharmaceutical and the food industries; natural antioxidants are also being used more and more widely. The Chinese quince fruits have an abundance of lignins with antioxidant properties; however, the lignins cannot be isolated by the methods conventionally used on other sources (e.g., wood, straw). In this investigation, multi-enzymatic hydrolytic pretreatments were used to isolate lignins from Chinese quince fruit, and the structures of these multi-enzyme mixture lignin (EML) fractions were then analyzed and compared with conventional cellulolytic enzyme lignin (CEL). EML fractions are structurally similar to CEL fractions except for an increased S/G ratio, greater number of β-O-4 linkages, higher average molecular weight and decreased thermal stability. The EML-2 fraction in particular seemed most representative of the lignins isolated, and it exhibited the highest antioxidant activity in comparison with CEL and other EML fractions.

Structural Characterization of Lignin and Lignin-Carbohydrate Complex (LCC) from Ginkgo Shells (Ginkgo biloba L.) by Comprehensive NMR Spectroscopy

Lignin and lignin-carbohydrate complexes are important polymers for lignocellulosic biorefinery and functional materials, but those in ginkgo shells are not effectively analyzed and exploited. Based on this background, milled wood lignins (MWL_ML and MWL_FZ) and lignin-carbohydrate complexes (LCC_ML and LCC_FZ) were isolated from the shells of Ginkgo biloba L. cv. Damaling (ML) and Ginkgo biloba L. cv. Dafozhi (FZ) correspondingly, and were structurally characterized by comprehensive NMR spectroscopy. The results showed that ginkgo shells exhibited higher lignin (42%) and xylan (20%) content than general softwood species. Isolated MWLs were rich in guaiacyl units with the presence of ferulates and p-coumarates, and the molecular formula was C₉H_7.93O_2.73(OCH₃)_0.81 and C₉H_7.87O_2.76(OCH₃)_0.88 for MWL_ML and MWL_FZ, respectively. Phenolic hydroxyl of MWL_ML (1.38 mmol/g) and MWL_FZ (1.23 mmol/g) in ginkgo shells was much less than that in general softwoods, suggesting a higher etherification and condensation degree of ginkgo shells lignin, and β-5′, α-O-4′, and 4-O-5′ bonds were the main condensed structures. O-acetylated β-d-xylopyranoside and β-d-mannopyranoside were the main polysaccharides associated with lignin, and the acetyl groups frequently acylate the C₂ and C₃ positions. LCC_ML had more phenyl glycoside (0.035/Ar) and less γ-ester (0.026/Ar) linkages than LCC_FZ.

Bio-based polyurethane foam preparation employing lignin from corn stalk enzymatic hydrolysis residues

Enzymatic hydrolysis residues (EHR) from corn stalk are industrial waste from the cellulosic ethanol industry. Lignin was separated as a bio-based polyol from EHR replacing partial petroleum-based polyether polyol to prepare bio-based polyurethane (BPU) foams without any other biomass pretreatment. Single factor experiment and response surface methodology (RSM) were employed to optimize separation conditions and reveal the significant influence of the interaction of conditions on the yield of separated lignin (SL). The effect of SL content (2.5, 5.0, 7.5, 10 and 15%) on the foams morphology and mechanical properties was assessed. Scanning electron microscopy (SEM) results implied that the cell shape was considerably affected by the large SL content, which contributed to an irregular, inhomogeneous, and thick cell wall. An astonishing 9.56 times increase in the compressive modulus and exponential 97.93 times boost in the compressive strength of BPU foams were attributed to the content of 15% SL without any further surface chemical modification. This present paper reports a green, potential and promising method for complete utilization of lignin from EHR in consideration of their abundant supply to greatly enhance the mechanical properties of BPU foams.

Enzymatic hydrolysis residues (EHR) from corn stalk are industrial waste from the cellulosic ethanol industry.

Quantification of Lignin and Its Structural Features in Plant Biomass Using 13C Lignin as Internal Standard for Pyrolysis-GC-SIM-MS

Understanding the mechanisms underlying plant biomass recalcitrance at the molecular level can only be achieved by accurate analyses of both the content and structural features of the molecules involved. Current quantification of lignin is, however, majorly based on unspecific gravimetric analysis after sulfuric acid hydrolysis. Hence, our research aimed at specific lignin quantification with concurrent characterization of its structural features. Hereto, for the first time, a polymeric ¹³C lignin was used as internal standard (IS) for lignin quantification via analytical pyrolysis coupled to gas chromatography with mass-spectrometric detection in selected ion monitoring mode (py-GC-SIM-MS). In addition, relative response factors (RRFs) for the various pyrolysis products obtained were determined and applied. First, ¹²C and ¹³C lignin were isolated from nonlabeled and uniformly ¹³C labeled wheat straw, respectively, and characterized by heteronuclear single quantum coherence (HSQC), nuclear magnetic resonance (NMR), and py-GC/MS. The two lignin isolates were found to have identical structures. Second, ¹³C-IS based lignin quantification by py-GC-SIM-MS was validated in reconstituted biomass model systems with known contents of the ¹²C lignin analogue and was shown to be extremely accurate (>99.9%, R² > 0.999) and precise (RSD < 1.5%). Third, ¹³C-IS based lignin quantification was applied to four common poaceous biomass sources (wheat straw, barley straw, corn stover, and sugar cane bagasse), and lignin contents were in good agreement with the total gravimetrically determined lignin contents. Our robust method proves to be a promising alternative for the high-throughput quantification of lignin in milled biomass samples directly and simultaneously provides a direct insight into the structural features of lignin.

Effect of alkaline preswelling on the structure of lignins from Eucalyptus

A clear elucidation of structural feature of whole lignin in plant cell wall is of great importance for understanding lignin biosynthesis mechanism and developing lignin based chemicals or materials under the current biorefinery scenario. Swollen residual enzyme lignin (SREL) has been identified as an ideal representative for native lignin in the plant walls. To investigate the influence of preswelling conditions on the structural features, the SREL obtained through preswelling the ball-milled Eucalyptus wood powder in 2, 4 and 8% NaOH solutions and subsequent in-situ enzymatic hydrolysis were thoroughly characterized. A cellulolytic enzyme lignin (CEL) was also prepared as a comparison. The quantitative NMR analyses indicated that the relative contents of β-O-4′ linkages in SRELs were higher than that in CEL. The lignin structure tended to undergo more destruction with the elevated NaOH concentration. A relatively low NaOH concentration (2% in this study), which could be applied to effectively remove hemicelluloses and transform cellulose structure from cellulose I to cellulose II, was competent to prepare SREL as an ideal representative for the protolignin. An optimization of SREL preparation was essential for a better understanding of the whole protolignin.

Tricin-lignins: occurrence and quantitation of tricin in relation to phylogeny

Tricin [5,7-dihydroxy-2-(4-hydroxy-3,5-dimethoxyphenyl)-4H-chromen-4-one], a flavone, was recently established as an authentic monomer in grass lignification that likely functions as a nucleation site. It is linked onto lignin as an aryl alkyl ether by radical coupling with monolignols or their acylated analogs. However, the level of tricin that incorporates into lignin remains unclear. Herein, three lignin characterization methods: acidolysis; thioacidolysis; and derivatization followed by reductive cleavage; were applied to quantitatively assess the amount of lignin-integrated tricin. Their efficiencies at cleaving the tricin-(4'-O-β)-ether bonds and the degradation of tricin under the corresponding reaction conditions were evaluated. A hexadeuterated tricin analog was synthesized as an internal standard for accurate quantitation purposes. Thioacidolysis proved to be the most efficient method, liberating more than 91% of the tricin with little degradation. A survey of different seed-plant species for the occurrence and content of tricin showed that it is widely distributed in the lignin from species in the family Poaceae (order Poales). Tricin occurs at low levels in some commelinid monocotyledon families outside the Poaceae, such as the Arecaceae (the palms, order Arecales) and Bromeliaceae (Poales), and the non-commelinid monocotyledon family Orchidaceae (Orchidales). One eudicotyledon was found to have tricin (Medicago sativa, Fabaceae). The content of lignin-integrated tricin is much higher than the extractable tricin level in all cases. Lignins, including waste lignin streams from biomass processing, could therefore provide a large and alternative source of this valuable flavone, reducing the costs, and encouraging studies into its application beyond its current roles.