Characterization of the radical scavenging activity of lignins--natural antioxidants

Guidelines for Evaluating the Antioxidant Activity of Lignin via the 2,2-diphenyl-1-picrylhydrazyl (DPPH) Assay

The most widespread procedure to measure the antioxidant activity of lignin is via the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. So far, different experimental procedures (i. e., different solvent, time, etc.) have been used to implement the DPPH methodology without estimating the effect of such modifications on the experimental procedure. To overcome this issue, the impact of the solvent, the time, and the type of substrate on the evaluation of the antioxidant activity (AoA) of lignin via the DPPH assay was investigated in this work. We found that multiple different parameters affect the evaluation of the AoA of lignin: i) the stability of the DPPH radical and the lignin solubility in a given solvent; ii) the importance of reaching steady state (the effect of time); iii) the background noise associated with lignin absorbance at λ=515 nm (used to monitor the DPPH radical scavenging); iv) lignin structure; v) providing a normalized radical scavenging index (nRSI); vi) comparing nRSI vs. inhibition percentage (IP) values. Overall, our investigation allowed us to provide guidelines on how to perform the DPPH assay for a more reliable evaluation of lignin AoA.

Innovative antimicrobial lignins: Extraction and characterization for advanced hydrogel applications

The antioxidant and antimicrobial activities of lignin are often emphasized; however, not every type exhibits these properties. In this work, water-soluble fractions of alkali lignin (AL), poly-(caffeyl alcohol) lignin (PCFA), pyrolytic lignin (PL) and grape seed lignin (GSL) were prepared. The original and water-soluble lignin fractions were comprehensively characterized using high-resolution 2D NMR spectroscopy. Notably, water-soluble fractions of PCFA, PL and GSL lignins exhibited 3.6 to 3.9 higher antioxidant activities than the original lignins despite having a phenolic content of approximately 12 % to 55 % lower. Additionally, these fractions demonstrated antimicrobial activities against Micrococcus luteus, Serratia marcescens and Escherichia coli. The potential of water-soluble lignin fractions as active modifiers for physically crosslinked hydrogels was also investigated. Specifically, PL/F lignin served as an antioxidant and antimicrobial agent for modifying carrageenan without disrupting its viscoelastic and swelling behaviour. Carrageenan hydrogels with 6 % PL/F lignin showed an antioxidant activity of 219.6 mg TE g-1 hydrogel and reduction rates of 43.9 % against M. luteus, 31.6 % against S. marcescens and 20.6 % against E. coli.

Study of antioxidant properties of sulfomethylated lignin and its application in pesticide dispersants

The utilization of lignin as a dispersant and protective agent for pesticide is a promising strategy for its high-value application, however, its use is limited by the poor solubility of lignin. In this study, the solubility and antioxidant performance of lignin were enhanced by treating it with Fenton's reagent and sulfomethylation reaction. The product has a sulfur content of up to 6.57 % and a DPPH radical scavenging capacity of up to 70 %. The resulting product, sulfomethylated lignin (SFKL) exhibited excellent antioxidant and dispersant properties for emamectin benzoate (EB). The samples containing sulfomethylated lignin exhibited smaller particle sizes and higher suspension rates after accelerated thermal storage than the samples containing commercially available lignosulfonate (SL). The average particle size of the sample using the best sample SFKL3-3 as dispersant was 1.40 nm and the suspension rate was 96.2 %. The emamectin benzoate retention was 76 % after 25 h of ultraviolet exposure. The adsorption properties of sulfomethylated lignin on emamectin benzoate particles were also investigated in this study, revealing that a significant amount of sulfomethylation lignin was adsorbed on the surface of emamectin benzoate particles, the maximum adsorption on the surface of EB particles, Qmax, was up to 12.60 mg/g. The Lignin adsorbed on the surface can not only scavenge the free radicals generated by photo-oxidation but also enhances the dispersion stability of the suspension.

Supramolecular room-temperature flowable lignin (RTFL)/MXene for sustainable coatings

Thermoelectric coatings with high biomass content, excellent storage stability, and solvent-free curing capabilities are highly desirable yet challenging. In this study, we demonstrate that supramolecular room-temperature flowable lignin (RTFL) was introduced as an effective carrier for the two-dimensional conductive material MXene, facilitating the development of supramolecular sustainable coatings. Lignosulfonic acid (LA) and polymerizable quaternary ammonium salt monomers were successfully utilized to synthesize the RTFL with ultra-low glass transition temperatures (-67--38 °C) using a deep eutectic strategy, with lignin content reaching up to 50 wt% without relying on traditional solvents. The RTFL demonstrated, serving as a macromolecular solvent, effectively dispersing and stabilizing MXene while preventing long-term oxidation. When directly coated onto various substrates and subsequently subjected to rapid photopolymerization, the RTFL/MXene coating exhibited remarkable photo-thermal-electric conversion properties. These features meet the requirements of various electrical applications, including Stirling engines and battery charging lamps. This supramolecular approach offers a pathway for developing high biomass content coatings suitable for environmental and energy-related applications.

Extraction of lignin from sustainable lignocellulosic food waste resources using a green deep eutectic solvent system and its property characterization

Food waste, an abundant and widely available lignocellulosic biomass is a potential feedstock for recovering value-added products like lignin possessing various valuable properties through valorisation thereby minimizing its disposal and hence detrimental impact to the environment. The present study investigates the efficacy of the choline chloride-oxalic acid DES system for extracting lignin biomaterial from a variety of food wastes namely potato peel, onion skin, tea residues, banana peel and pomegranate peel wastes and its properties. The extraction experiments were carried out at 100°C for 6h using DES with a solid-to-liquid ratio of 1: 10 (w/v). The yield and purity of the extracted lignin from different biowastes were determined. A varied yield and purity of lignin was obtained depending on the sources of waste biomass. However, the highest lignin yield of 22.439 ± 4.38 % and purity of 77 ± 1.95 % was obtained with pomegranate peel. A comparable lignin yield (21.348 ± 2.40 %) and purity (75 ± 1.26 %) was also achieved with banana peel. UV-Visible and FTIR analyses revealed the existence of aromatic and major functional groups of lignin. XRD analysis confirmed its amorphous nature and its spherical or ellipsoidal morphology revealed by FESEM image analysis. The presence of hydroxyl ions, phenols, and carboxylic acids, and protons in the methoxy group and aliphatic and aromatic moieties in the lignin were identified by negative zeta potential values and 1H NMR spectra analysis respectively. The quantity of major linkages like β-O-4', β - 5' and β - β' in the lignin was determined by 2D-HSQC NMR. The lignin also exhibited antimicrobial and antioxidant activities. The elemental composition and higher heating values were determined by CHNSO analysis. Overall, pomegranate and banana peels are the most prospective food wastes found in this study for extracting lignin with high yield. The study further demonstrated the potentiality of the green DES for food waste valorisation to extract lignin.

Sustained ROS Scavenging and Pericellular Oxygenation by Lignin Composites Rescue HIF-1α and VEGF Levels to Improve Diabetic Wound Neovascularization and Healing

Although delayed wound healing is an important clinical complication in diabetic patients, few targeted treatments are available, and it remains a challenge to promote diabetic wound healing. Impaired neovascularization is one of the prime characteristics of the diabetic phenotype of delayed wound healing. Additionally, increased levels of reactive oxygen species (ROS) and chronic low-grade inflammation and hypoxia are associated with diabetes, which disrupts mechanisms of wound healing. We developed lignosulfonate composites with several wound healing properties, including sustained oxygen release through calcium peroxide nanoparticles and reactive oxygen species and free radical scavenging by thiolated lignosulfonate nanoparticles. Sustained release of oxygen and ROS-scavenging by these composites promoted endothelial cell (EC) branching and characteristic capillary-like network formation under high glucose conditions in vitro. Gene co-expression network analysis of RNA-sequencing results from ECs cultured on lignin composites showed regulation of inflammatory pathways, alongside the regulation of angiogenic hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth (VEGF) factor pathways. In vivo, lignosulfonate composite treatment promoted VEGF expression and angiogenesis in full thickness skin wounds in diabetic mice, a model of delayed wound healing. Treatment of diabetic wounds with lignosulfonate composites also promoted faster epithelial gap closure and increased granulation tissue deposition by day 7 post-wounding, with a higher presence of pro-healing type macrophages. Our findings demonstrate that lignosulfonate composites promote diabetic wound healing without requiring additional drugs. This highlights the potential of functionalized lignosulfonate for wound healing applications that require balanced antioxidation and controlled oxygen release. STATEMENT OF SIGNIFICANCE: The lignosulfonate composites developed in this study offer a promising solution for delayed wound healing in diabetic patients. By effectively addressing key factors contributing to the multifaceted pathophysiology of the diabetic wounds, including impaired neovascularization, increased ROS levels, and chronic inflammation and wound proteolysis, these composites demonstrate significant potential for promoting wound repair and reducing the complications associated with diabetic wounds. The unique combination of pro-angiogenic, oxygen-releasing, ECM remodeling and antioxidant properties in these lignosulfonate-based materials highlights their potential as a valuable therapeutic option, providing a multi-pronged approach to diabetic wound healing without the need for additional drugs.

Enhancing Lignin-Carbohydrate Complexes Production and Properties With Machine Learning

Lignin-carbohydrate complexes (LCCs) present a unique opportunity for harnessing the synergy between lignin and carbohydrates for high-value product development. However, producing LCCs in high yields remains a significant challenge. In this study, we address this challenge with a novel approach for the targeted production of LCCs. We optimized the AquaSolv Omni (AqSO) biorefinery for the synthesis of LCCs with high carbohydrate content (up to 60/100 Ar) and high yields (up to 15 wt %) by employing machine learning (ML). Our method significantly improves the yield of LCCs compared to conventional procedures, such as ball milling and enzymatic hydrolysis. The ML approach was pivotal in tuning the biorefinery to achieve the best performance with a limited number of experimental trials. Specifically, we utilized Bayesian Optimization to iteratively gather data and examine the effects of key processing conditions-temperature, process severity, and liquid-to-solid ratio-on yield and carbohydrate content. Through Pareto front analysis, we identified optimal trade-offs between LCC yield and carbohydrate content, discovering extensive regions of processing conditions that produce LCCs with yields of 8-15 wt % and carbohydrate contents ranging from 10-40/100 Ar. To assess the potential of these LCCs for high-value applications, we measured their glass transition temperature (Tg), surface tension, and antioxidant activity. Notably, we found that LCCs with high carbohydrate content generally exhibit low Tg and surface tension. Our biorefinery concept, augmented by ML-guided optimization, represents a significant step toward scalable production of LCCs with tailored properties.

Characterization and antioxidant activity of differentiated fractionation lignin from corn stover

Lignin contains many chemical functional groups with multiple biological activities. However, the heterogeneity of lignin such as complex structure and high polydispersity, and poor dissolution performance hinders its value-added application. In this study, it was found that there was a significant difference in the solubility of the chemical components of corn stover alkali-extracted lignin-carbohydrate complex (CSALCC) in a 0.6 M NaHCO3 solution. Herein, CSALCC was fractionated using a 0.6 M NaHCO3 solution, hot water, acid precipitation, and macroporous adsorption resin D101 column chromatography to afford fraction F1-1, F2, and F3-1. To demonstrate the improvement in composition, water solubility and antioxidant activity of the fractions. The characterization techniques UV, FTIR, NMR, TGA, SDS-PAGE and GPC were employed. Antioxidant activities were evaluated by ABTS, ORAC and ferric reducing power assay. F1-1 consists mainly of hemicellulose and is soluble in deionized water. F2 is a more water-soluble lignin than CSALCC, which is conducive to the development of value-added products of lignin in aqueous systems. F3-1 was acidic-soluble lignin with the highest total polyphenol content of all fractions, and exhibited higher water solubility, antioxidant properties and UV absorption. F3-1 may have potential application in cosmetics, pharmaceuticals, the food processing field.

Bioactive lignin from maleic acid hydrotropic fractionation: Revealing the structural-bioactivity relationship

Lignin possesses diverse bioactivities due to its unique physicochemical structure. This study investigates the structural-bioactivity relationships of lignin derived from maleic acid hydrotropic fractionation (MAHF) of two types of herbaceous biomass. The results indicated that lignin with higher phenolic hydroxyl (-OH) content (up to 2.0 mmol/g) and carboxyl (-COOH) groups (up to 0.89 mmol/g) exhibited significantly enhanced antioxidant activity. The highest antioxidant of MAHF lignin (MAHL) reached 98 % for scavenging DPPH (2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl) at 0.56 mg/mL. Antibacterial tests revealed that MAHLs demonstrated inhibition rates of 66 % against E. coli and 54 % against S. aureus at 10 mg/mL. MAHLs at 1 mg/mL concentration blocked >98 % of UV radiation. Furthermore, the study demonstrated that lignin with higher phenolic hydroxyl (-OH), carboxyl (-COOH), and syringyl (S) units and conjugated double bonds exhibit enhanced bioactive properties. Lignin with lower Mw and PDI also tends to possess good bioactivities. The findings from the study can facilitate the application of lignin as an efficient, cost-effective, and renewable biopolymer additive in various industries.

Enhanced Antioxidation and UV-Absorption Ability of Industrial Lignin via Promoting Phenolic Contents and Hydrophilicity

Lignin possesses unique natural antioxidation and UV-absorption abilities, making it a promising ingredient for sunscreen. However, the industrial lignin produced from pulping or bioethanol production generally shows low efficiency due to the limited phenolic hydroxyl content and poor compatibility with sunscreen, respectively. To address this issue, a molten salt hydrate treatment process was carried out for the selective cleavage of ether bonds in industrial lignin. After treatment, a 2-fold increase in phenolic hydroxyl content was observed, and lignin antioxidation efficiency was improved. The intermolecular forces of lignin in water measured by an atomic force microscope showed a significant decrease from -1.46 to 0.46 mN/m, suggesting an efficient increase in lignin hydrophilicity, which promoted lignin compatibility with sunscreen. We converted industrial lignin into colloidal balls, which improved compatibility and dispersion in the cream and more than tripled the sun protection factor compared to the direct addition of industrial lignin.

Progress on oxygen-releasing bioactive polymeric scaffolds in tissue engineering and biomedical treatment: A review

Tissue engineering presents promising avenues for addressing issues related to tissue defects and regenerative medicine. However, the translational efficacy of tissue engineering in clinical settings remains limited, primarily due to the inadequate survival rates of implanted tissue scaffolds. This is attributed to the grafts' inability to adequately supply oxygen and their dependence on the diffusion of oxygen from surrounding tissues for tissue regeneration. The integration of oxygen-releasing materials in human tissue engineering is anticipated to enhance the hypoxic microenvironment for tissue regeneration. In recent years, a variety of oxygen-producing or oxygen-carrying biomacromolecules, including gelatin, chitosan, and alginate, have been developed, offering innovative strategies for controlled drug release efficacy, regenerative medicine, and biological systems engineering. This review examines applications of these oxygen-releasing biological macromolecules, primarily derived from natural polymeric materials, in diverse facets of human tissue engineering including skin, heart tissue, tumor therapy. We also highlight recent advancements in this field, with an emphasis on current challenges, potential solutions, and future perspectives.

Construction of Iron-Modified Lignin-Based Nanomicrocapsules for Enhancing the Functionality of Natural Product-Based Pesticides

To address the issue of low pesticide utilization owing to poor dispersibility, low leaf surface adhesion, and poor transport within plants, this study exploits electrostatic interactions between sodium lignosulfonate (SL) and dodecyltrimethylammonium chloride (DTAC) to induce self-assembly, followed by iron ion (Fe3+) chelation and loading with a natural product-based pesticide, rosin-based triazole derivative (RTD), yielding RTD@SL-DTAC-Fe nanomicrocapsules (NMs). It is worth noting that the presence of Fe3+ enhances the dispersibility of the NMs. The water dispersibility and photostability of RTD are significantly improved after encapsulation, and a stimulus response to laccase is achieved. Leaf-washing experiments confirm the enhanced adhesion of RTD@SL-DTAC-Fe NMs to the surface of rice plant leaves compared to that of free RTD. Fluorescently labeled NMs exhibit bidirectional transport within rice plants, and RTD@SL-DTAC-Fe NMs demonstrates better transport performance than RTD. In vitro and in vivo antifungal tests indicate that encapsulation by NMs significantly enhanced pesticide activity. Field trials demonstrate that NMs exhibited prolonged efficacy compared to RTD. Finally, the safety evaluation confirms the environmental friendliness of the NMs. This study provides valuable insight for optimizing and improving the utilization efficiency and biosafety of natural product-based pesticides.

Exploring the relationship between lignin structure and antioxidant property using lignin model compounds

Lignin has a natural polyphenol structure that is expected to replace chemically synthesized antioxidants as a native antioxidant with biodegradable and convenient source characteristics. However, the improvement of the antioxidant property of lignin and its application as an antioxidant are still somewhat limited due to the lack of understanding of the relationship between specific lignin structures and antioxidant property. Therefore, the study of the relationship between lignin structure and antioxidant property is crucial to realize the high-quality application of lignin. In this experiment, the scavenging ability of free 1,1-diphenyl-2-picrylhydrazyl (DPPH·) radicals was determined for different grades of acetylated tannins, typical lignin model compounds and different structural units of milled wood lignin to investigate the relationship between lignin structure and antioxidant property. Based on the experimental results, some structure-activity relationships were proposed and the mechanism of the antioxidant property of lignin was discussed. The number of phenolic hydroxyl groups was linearly and positively correlated with antioxidant property, and the scavenging of DPPH radicals increased significantly with the increase in the number of methoxy groups in the model compounds. Moreover, aldehyde and carboxyl groups had a negative effect on the antioxidant property of lignin, while methoxy, alkyl and alcohol hydroxyl groups played a positive role. The guaiacyl (G) and syringyl (S) units favored the antioxidant property, so the difference in the content of structural units in lignin under certain conditions of phenolic hydroxyl content also affected the antioxidant property. Therefore, the antioxidant property of aspen milled lignin was higher than that of other milled lignin from different wood species. Finally, the mechanism of DPPH free radical scavenging by lignin was revealed to better understand the relationship between lignin structure and antioxidant property.

Minimizing food oxidation using aromatic polymer: From lignin into nano-lignin

Food loss and waste caused by oxidation result in environmental and economic losses and health threats. Lignin is an abundant aromatic polymer with varied antioxidant capacity, which can reduce food oxidation caused by radical species exposure. The lignin antioxidant strength can be influenced by source, type, structure, processing, degradation products, chemical modifications, and particle size. Lignin in micro- or nano-particles has high reactivity and is associated with increased surface area to improve antioxidant capacity. Lignin can be used as a food additive to suppress lipid and protein oxidation, although its effect on fruit/vegetable oxidation needs to be discussed. The lignin antioxidant properties are promising to be applied in food industries, such as food additives, animal feed supplements, and antioxidant packaging designs. However, there are challenges and limitations to consider, such as the potential for toxicity reactions in some individuals and the need for further research to understand its effects on different food products fully. As a feed nutrition, lignin can improve meat quality. Meanwhile, loading lignin in the packaging matrix can extend the food shelf life through antioxidant and antimicrobial activities, and UV-block. Lignin also improves packaging properties (conventional and 3D-printing fabrication) to maintain food quality, e.g., changes in mechanical properties, hydrophobicity, water vapor permeability, and other influences. This article reviews lignin's role as a natural antioxidant in the food industry. Future directions and discussions relate to prooxidative mechanisms, toxicity, fruit and vegetable preservation mechanisms, inhibition of protein oxidation, activity to food enzymes (fruit ripening enzyme activators and inhibitors of cellulase and β-glucosidase enzyme), dispersity in packaging matrices, and material diversification for 3D printing.

Efficient extraction of light-colored lignin from bamboo by p-toluenesulfonic acid assisted tetrahydrofurfuryl alcohol aqueous solution

Acidic hydrotropes exhibit effective performance in fractionating the constituents of lignocellulosic biomass owing to their amphiphilic characteristics. However, the requirement for excessively high concentrations may lead to the condensation and aggregation of lignin. In this case, bamboo was extracted with 70 % (w/v) tetrahydrofurfuryl alcohol (THFA) aqueous solution containing 5-20 % (w/v) p-toluenesulfonic acid (pTsOH) at 90-120 °C for 1-4 h. Results indicated that 91 % of lignin was efficiently removed from bamboo, with subsequent recovery of 73.5 % achieved through extraction with 10 % pTsOH at 110 °C for 4 h. Furthermore, the resulting lignin exhibited a relative content of β-O-4 bonds of 64.1 %, displayed a light color (L*: 70.48), boasted a purity of 99.64 %, and possessed a moderate molecular weight. These attributes position it as a valuable candidate in functional material production. The aqueous solution provides an ideal medium for efficient extraction of uncondensed, light-colored lignin, thereby furnishing insights for advancing the utilization.

Increased Antioxidant Performance of Lignin by Biodegradation Obtained from an Extract of the Mushroom Pleurotus eryngii

The aim of this study was to evaluate the antioxidant properties of the products derived from the biodegradation of lignin by the ligninolytic enzymes present in an aqueous extract of the mushroom P. eryngii. A mixture obtained after the incubation of lignin for 18 h with P. eryngii extract was tested in vitro for its total polyphenol content, reducing power, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl (OH) radical-scavenging activities. The results showed that the enzymatic treatment of lignin enhanced its antioxidant performance. The biocompatibility of the products of lignin biodegradation and their ability to scavenge reactive oxygen species (ROS) were also tested on the astrocytic cell line DI-TNC1. The results obtained indicated that a lignin mixture incubated for 18 h does not affect cell viability or inhibit the H2O2-induced ROS production. These results suggest that the enzymatic degradation of lignin represents an efficient and ecofriendly approach to obtain lignin derivatives potentially useful for antioxidant applications.

Lignin hydrogel sensor with anti-dehydration, anti-freezing, and reproducible adhesion prepared based on the room-temperature induction of zinc chloride-lignin redox system

In recent years, flexible sensors constructed mainly from hydrogels have received increasing attention. However, conventional hydrogels need to be prepared by high-temperature or radiation-induced polymerization reactions, which limits their practical applications due to their suboptimal electrical conductivity and weak mechanical properties. In this paper, using sodium lignosulfonate as the raw material, a dynamic catechol-quinone redox system formed by lignin‑zinc ions was constructed to initiate rapid free radical polymerization of acrylamide (AM) monomer at room temperature. In addition, Deep eutectic solvent (DES) can form a strong hydrogen bonding network within the molecules and between the molecules of the hydrogel, resulting in a hydrogel with good tensile properties (hydrogel elongation at break of 727.19 %, breaking strength of 84.09 kPa), and provides the hydrogel with high electrical conductivity, anti-dehydration, anti-freezing, and anti-bacterial properties. Meanwhile, the addition of lignin also improved the adhesion and UV resistance of the hydrogel. This hydrogel assembled into a flexible sensor can sense various small and large amplitude movements such as nodding, smiling, frowning, etc., and has a wide range of applications in flexible sensors.

A high-efficiency strategy for fruit preservation using green, natural raw materials

Straw is an abundant renewable biomass resource material. Lignin contained in straw is a unique natural aromatic compound in nature. At present, it is urgent to find ways to realize the higher value of natural lignin resources. In this study, alkali lignin was separated from rice straw by hydrothermal method in NaOH solution, which was prepared lignin nanoparticles by a simple green anti-solvent method. The obtained lignin nanoparticles had excellent anti-tyrosinase activity (IC50 = 0.329 mg mL-1) and anti-oxidation performance (IC50 = 0.0451 mg mL-1). Meanwhile, through the analysis of tyrosinase inhibition kinetics, it is concluded that the tyrosinase inhibition by lignin nanoparticles belongs to mixed inhibition. The affinity of lignin nanoparticles to the free enzyme is greater than that of enzyme and substrate complex. In addition, lignin nanoparticles were added to chitosan solution for compounding, then the composite films for fruit preservation were prepared by casting method. The experimental results show that the composite membrane can effectively extend the shelf life of fruits, which is expected to achieve a broader application in the field of fruit preservation and food packaging.

Insights into the Chemical Structure and Antioxidant Activity of Lignin Extracted from Bamboo by Acidic Deep Eutectic Solvents

Deep eutectic solvents (DESs) composed of choline chloride as hydrogen bond acceptors (HBAs) and six organic acids as hydrogen bond donors (HBDs) were used to extract lignin from bamboo (Phyllostachys edulis (Carrière) J. Houz.). The structures of the DES-extracted lignin samples were analyzed by Fourier-transform infrared spectroscopy (FT-IR), UV-visible spectroscopy (UV-vis), thermogravimetric analysis (TG), and gel permeation chromatography (GPC) to investigate the relationship between the chemical structure of lignin and its antioxidant activity. The results showed that DES treatment removed a large portion of the lignin (73.37-86.38%) from bamboo, and the chemical structure of lignin was changed due to the use of different types of HBDs. The extracted lignin exhibited good UV-vis light shielding properties, thermal stability, and antioxidant activity. Moreover, the total phenolic hydroxyl content of lignins was positively correlated with their antioxidant activity, while the molecular weight of lignins was negatively correlated with their antioxidant activity. Notably, lignin extracted with choline chloride-p-toluenesulfonic acid had the highest phenolic hydroxyl content and lower molecular weight, showing the strongest antioxidant activity (IC50 DPPH = 417.69 μg/mL, IC50 ABTS = 58.62 μg/mL). This study confirms the high thermal stability, excellent antioxidant activity, and UV shielding properties of lignin extracted with choline chloride-organic acid DESs, suggesting its potential application in the fields of antioxidants and material modifiers.

Use of Renewable Alcohols in Autocatalytic Production of Aspen Organosolv Lignins

This study aimed to investigate the intrinsic efficiency of renewable alcohols, applied under autocatalytic conditions, for removing lignin from aspen and hot-water-extracted aspen while substantially preserving the lignin structure so as to facilitate various valorization strategies. Ethylene glycol (EG), propylene glycol (PG), 1,4-butanediol (BDO), ethanol (EtOH), and tetrahydrofurfuryl alcohol (THFA) were evaluated based on their lignin solubilization ability, expressed as the relative energy difference (RED) following the principles of the Hansen solubility theory. The findings indicate that alcohols with a higher lignin solubilization potential lead to increased delignification, almost 90%, and produce a lignin with a higher content of β-O-4 bonds, up to 68% of those found in aspen milled wood lignin, thereby indicating their potential for valorization through depolymerization. However, these alcohols also produce lignin with a higher content of β-β and β-5 bonds, resulting in a higher molecular weight and polydispersity, due to readily occurring homolytic reactions. Hot-water extraction (HWE) conducted prior to alcohol treatment reduced the delignification efficiency and resulted in a lignin with a lower β-O-4 bond content. The lignins produced in these experiments exhibited a superior UV-A absorption capacity compared with synthetic benzophenone, as well as a greater radical quenching ability than synthetic butylated hydroxytoluene, indicating their potential for use in the protection of polymers against degradation.

The Enhancement Origin of Antioxidant Property of Carboxylated Lignin Isolated from Herbaceous Biomass Using the Maleic Acid Hydrotropic Fractionation

Lignin is endowed with antioxidant activity due to its diverse chemical structure. It is necessary to explore the relationship between antioxidant activity and the chemical structure of the lignin to develop its high-value utilization. Herein, we employed maleic acid (MA) as a hydrotropic agent to preferably isolate the lignin from distinct herbaceous sources (wheat straw and switchgrass) under atmospheric pressure conditions. The resultant acid hydrotropic lignin (AHL) isolated from wheat straw exhibited high radical scavenging rates, up to 98% toward DPPH and 94% toward ABTS. Further investigations indicated that during the MA hydrotropic fractionation (MAHF) process, lignin was carboxylated by MA at γ-OH of the side-chain, providing additional antioxidant activity from the carboxy group. It was also found that the radical scavenging rate of AHL has a positive correlation with carboxyl, phenolic hydroxyl contents, and the S-G (syringyl-guaiacyl) ratio, which could be realized by increasing the MAHF severity. Overall, this work underlies the enhancement origin of the antioxidant property of lignin, which will facilitate its application in biological fields as an efficient, cheap, and renewable antioxidant additive.

Lignin Structural Characterization and Its Antioxidant Potential: A Comparative Evaluation by EPR, UV-Vis Spectroscopy, and DPPH Assays

The natural aromatic polymer lignin and its lignin-like oligomeric fragments have attracted attention for their antioxidant capacity and free radical scavenging activities. In this study, a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was employed to assess the antioxidant capacity of fractionated and partially depolymerized organosolv lignin by electron paramagnetic resonance (EPR) and UV-Vis spectroscopy. The results show significant antioxidant activity for both the lignin and oligomeric fragments, with the EPR measurements demonstrating their efficiency in quenching the free radicals. The EPR data were analyzed to derive the kinetic rate constants. The radical scavenging activity (RSA) of lignins was then determined by UV-Vis spectroscopy and the results were compared with the EPR method. This two-method approach improves the reliability and understanding of the antioxidant potential of lignin and its derivatives and provides valuable insights for their potential applications in various industries, including pharmaceuticals, food preservation, and cosmetics.

Unraveling the structural aspects of microwave-assisted OrganoCat-based coconut shell lignins: An eco-friendly route for obtaining bio-based antioxidants

New routes for biomass valorization have been developing by the scientific community. The aim of this work was developing a novel OrganoCat-based protocol and deeply understand the structure of the obtained lignins. Microwave-assisted OrganoCat-based process was performed using a biphasic system (ethyl acetate and oxalic acid or HCl) at mild conditions. OrganoCat-based lignins (OCLs) were characterized by compositional analysis, FTIR, 1H, 13C, 1H13C HSQC, 31P NMR, TGA and GPC. The solubility of OCLs in different organic solvents and their antioxidant capacity against DPPH were investigated. The spectroscopic analyses showed that OCLs have high residual extractives and the lignin motifs were preserved. OCLs have presented lower thermal stability than MWL, but showed great antioxidant activities and high solubility in a wide range of organic solvents. A novel biorefinery protocol yielded coconut shell lignins with peculiar structural and compositional features and several technological applications through an eco-friendly, sustainable and relatively low-cost biphasic pulping process.

The Antimicrobial Properties of Technical Lignins and Their Derivatives-A Review

Lignin represents one of the most abundant plant-derived polymers. It is mostly present in the cell wall, and its primary role is to provide mechanical support to the plant. Chemical processes during wood-pulping yield diverse technical lignins with distinct characteristics. Due to their complex and variable nature, technical lignins are often undervalued and are mainly used as burning fuel in mills. However, various technical lignins have been shown to possess antimicrobial properties. Consequently, there is an increasing interest in understanding the properties and conditions that underlie their antimicrobial characteristics and how we can utilize them for practical applications. This review, for the first time, comprehensively summarized the antimicrobial activities of technical lignins and their potential antimicrobial applications.

Eco-friendly lignin nanoparticles as antioxidant and antimicrobial material for enhanced textile production

Natural polymers are bioactive compounds that are used in the treatment of several disorders. Natural lignin, an amorphous polymer, offers significant potential for use as a building block in the production of bio-renovation materials. This study used an alkaline solvent technique to extract lignin from two Egyptian cotton cultivar byproducts, Giza 86 and 90. We then created nano-lignin to recycle cotton stalks into an environmentally beneficial product. The characterization of L86, L90, LNP86, and LNP90 was carried out using particle size, zeta potential, FT-IR, and TEM. Antioxidant activity using the DPPH assay and antimicrobial activity were determined for lignin and nano-lignin. Seven pathogenic bacteria (Bacillus cereus, Staphylococcus aureus, Staphylococcus sciuri, Salmonella typhi, Salmonella enterica, Escherichia coli, and Pseudomonas aeruginosa) and five mycotoxigenic fungi (Aspergillus flavus, Aspergillus ochraceus, Aspergillus niger, Fusarium proliferatum and Penicillium verrucosum) were used for antimicrobial activity. The results showed high antioxidant efficiency for LNP90, with an IC50 of 10.38 µg/mL. The antimicrobial activity showed positive growth inhibition for all studied microorganisms, with significant differences in nano-lignin compared to ordinary lignin. lignin and nano-lignin were effectively applied to treated textiles for medical purposes. The study concluded that single-use medical textiles with anti-microbial and anti-oxidant properties, made from lignin and nano-lignin, could benefit patients intolerant to antibiotics.

Green Extraction of Reed Lignin: The Effect of the Deep Eutectic Solvent Composition on the UV-Shielding and Antioxidant Properties of Lignin

Lignin, the second most abundant natural polymer, is a by-product of the biorefinery and pulp and paper industries. This study was undertaken to evaluate the properties and estimate the prospects of using lignin as a by-product of the pretreatment of common reed straw (Phragmites australis) with deep eutectic solvents (DESs) of various compositions: choline chloride/oxalic acid (ChCl/OA), choline chloride/lactic acid (ChCl/LA), and choline chloride/monoethanol amine (ChCl/EA). The lignin samples, hereinafter referred to as Lig-OA, Lig-LA, and Lig-EA, were obtained as by-products after optimizing the conditions of reed straw pretreatment with DESs in order to improve the efficiency of subsequent enzymatic hydrolysis. The lignin was studied using gel penetration chromatography, UV-vis, ATR-FTIR, and 1H and 13C NMR spectroscopy; its antioxidant activity was assessed, and the UV-shielding properties of lignin/polyvinyl alcohol composite films were estimated. The DES composition had a significant impact on the structure and properties of the extracted lignin. The lignin's ability to scavenge ABTS+• and DPPH• radicals, as well as the efficiency of UV radiation shielding, decreased as follows: Lig-OA > Lig-LA > Lig-EA. The PVA/Lig-OA and PVA/Lig-LA films with a lignin content of 4% of the weight of PVA block UV radiation in the UVA range by 96% and 87%, respectively, and completely block UV radiation in the UVB range.

Targeted isolation, identification, and antioxidant evaluation of aromatic polyketides from a plant-derived fungus Ophiobolus cirsii LZU-1509

There are >350 species of the Ophiobolus genus, which is not yet very well-known and lacks research reports on secondary metabolites. Three new 3,4-benzofuran polyketides 1-3, a new 3,4-benzofuran polyketide racemate 4, two new pairs of polyketide enantiomers (±)-5 and (±)-7, two new acetophenone derivatives 6 and 8, and three novel 1,4-dioxane aromatic polyketides 9-11, were isolated from a fungus Ophiobolus cirsii LZU-1509 derived from an important medicinal and economic crop Anaphalis lactea. The isolation was guided by LC-MS/MS-based GNPS molecular networking analysis. The planar structures and relative configurations were mainly elucidated by NMR and HR-ESI-MS data. Their absolute configurations were determined by using X-ray diffraction analysis and via comparing computational and experimental ECD, NMR, and specific optical rotation data. 9 possesses an unreported 5/6/6/6/5 five-ring framework with a 1,4-dioxane, and 10 and 11 feature unprecedented 6/6/6/5 and 6/6/5/6 four-ring frames containing a 1,4-dioxane. The biosynthetic pathways of 9-11 were proposed. 1-11 were nontoxic in HT-1080 and HepG2 tumor cells at a concentration of 20 μM, whereas 3 and 5 exerted higher antioxidant properties in the hydrogen peroxide-stimulated model in the neuron-like PC12 cells. They could be potential antioxidant agents for neuroprotection.

Enhancing the anti-biofouling property of solar evaporator through the synergistic antibacterial effect of lignin and nano silver

Solar desalination is an effective solution to address the global water scarcity issue. However, biofouling poses a significant challenge for solar evaporators due to the presence of bacteria in seawater. In this study, an anti-biofouling evaporator was constructed using the synergistic antibacterial effect of lignin and silver nanoparticles (AgNPs). The AgNPs were easily synthesized using lignin as reductant under mild reaction conditions. Subsequently, the Lignin-AgNPs solution was integrated into polyacrylamide hydrogel (PAAm) without any purification steps, resulting in the formation of Lignin/AgNPs-PAAm (LAg-PAAm). Under the combined action of AgNPs and the hydroquinone groups present in oxidized lignin, LAg-PAAm achieved over 99 % disinfection efficiency within 1 h, effectively preventing biofilm formation in pore channels of solar evaporators. The anti-biofouling solar evaporator demonstrated an evaporation rate of 1.85 kg m-2 h-1 under 1 sun irradiation, and maintained stable performance for >30 days due to its high efficient bactericidal effect. Furthermore, it also exhibited exceptional salt-rejection capability attributed to its superior hydrophilicity.

Effect of DES lignin incorporation on physicochemical, antioxidant and antimicrobial properties of carboxymethyl cellulose-based films

Herein, three pretreated grapevine lignins were incorporated into carboxymethyl cellulose films. The effects of traditional NaOH pretreated lignin and DES (ChCl-LA, ChCl-LA & K2CO3-EG) pretreated lignin on film properties were compared. Modern analytical techniques were employed to systematically characterize the pretreated lignin and the different CMC-lignin films. The results showed that DES lignin was of high purity, low molecular weight, and homogeneous structure. It outperformed traditional NaOH lignin in terms of compatibility with CMC, enabling it to perform its bioactivity and physicochemical functions in films. This feature effectively enhanced the hydrophobicity, UV shielding ability, water vapor barrier, thermal stability, mechanical properties, and biological activity of CMC-DES lignin film. NMR (2D HSQC) showed that the excellent antioxidant and antibacterial capabilities of CMC-DES lignin film are due to the retention of butyl (S) and p-hydroxyphenyl (H) units in DES lignin, resulting in its rich phenolic hydroxyl content. The detailed structural elucidation of DES lignin's chemical interactions with CMC provided valuable insights into the advantageous properties observed in the films, presenting innovative solutions for applications in the food packaging and preservation industries.

Production of highly antioxidant lignin nanoparticles from a hardwood technical lignin

Eucalypt kraft lignin isolated in a LignoBoost™ pilot plant was characterized by GC-MS, ICP-OES, DSC, HPSEC, 31P NMR, and HSQC 2D-NMR to be used without any further processing to produce lignin nanoparticles (LNPs) by nanoprecipitation. Tetrahydrofuran (THF) was used as a solvent, and water as a non-solvent. Microscopic analysis (TEM) showed that LNPs were regularly spherical with some hollow particles dispersed in-between, and sizes were tunable by changing the solvent dripping rate onto the non-solvent. LNP particle sizes had a bimodal distribution, with the largest population having an average apparent hydrodynamic diameter ranging from 105.6 to 75.6 nm. Colloidal dispersions of LNPs in water presented good stability in different dilutions without significant size changes upon storage at pH close to neutral for as long as 45 days. Zeta potentials around -40 mV were obtained for LNP suspensions at pH ranging from 7 to 9. The high carbohydrate content (circa 10 % on a dry basis, mostly xylans) of the lignin precursor did not interfere in LNP formation, whose antioxidant activity was expressive as demonstrated by the ABTS assay at pH 7.4, with an EC50 of 4.04 μg mL-1. Also, the Trolox® equivalent antioxidant capacity (TEAC) of LNPs reached 1.90 after 40 min reaction time.

Interpretable Machine Learning and Reactomics Assisted Isotopically Labeled FT-ICR-MS for Exploring the Reactivity and Transformation of Natural Organic Matter during Ultraviolet Photolysis

Isotopically labeled FT-ICR-MS combined with multiple post-analyses, including interpretable machine learning (IML) and a paired mass distance (PMD) network, was employed to unravel the reactivity and transformation of natural organic matter (NOM) during ultraviolet (UV) irradiation. FT-ICR-MS analysis was used to assign formulas, which were classified on the basis of their molecular compositions and structural categories. Isotope (deuterium, D) labeling was utilized to unequivocally determine the photochemical products and examine the development of OD radical-mediated NOM transformation. With regard to the reactive molecular formulas, CHOS formulas exhibited the highest reactivity (86.5% of precursors disappeared) followed by CHON (53.4%) and CHO (24.6%) formulas. With regard to structural categories, the degree of reactivity decreased in the following order: tannins > condensed aromatics > lignin/CRAMs. The IML algorithm demonstrated that the crucial features governing the reactivity of formulas were the molecular weight, DBE-O, NOSC, and the presence of heteroatoms (i.e., N and S), suggesting that the large and unsaturated compounds containing S and N are more prone to photodegradation. The reactomics approach using the PMD network further indicated that 11 specific molecular formulas in the CHOS and CHO class served as hubs, implying a higher photoreactivity and participation in a range of transformations. The isotope labeling analyses also found that, among the reactions observed, hydroxylation (i.e., +OD) is dominant for lignin/CRAMs and condensed aromatics, and formulas containing ≤10 D atoms were developed. Overall, this study, by adopting rigorous and interpretable techniques, could provide in-depth insights into the molecular-level dynamics of NOM under UV irradiation.

Study toward a More Reliable Approach to Elucidate the Lignin Structure-Property-Performance Correlation

The correlation between lignin structure, its properties, and performance is crucial for lignin engineering in high-value products. Currently, a widespread approach is to compare lignins which differ by more than one parameter (i.e., Kraft vs organosolv vs lignosulfonates) in various applications by attributing the changes in their properties/performance specifically to a certain variable (i.e., phenolic -OH groups). Herein, we suggest a novel approach to overcome this issue by changing only one variable at a time while keeping all others constant before investigating the lignin properties/performance. Indulin AT (Ind-AT), a softwood Kraft lignin, was chosen as the model substrate for this study. Selective (analytical) lignin modifications were used to mask/convert specific functionalities, such as aliphatic (AliphOH) including benzylic -OH (BenzOH) and phenolic -OH (PhOH) groups, carboxyl groups (-COOH) and carbonyl groups (CO) via methylation, acetylation, and reduction. The selectivity and completeness of the reactions were verified by comprehensive NMR analysis (31P and 2D HSQC) of the modified preparations together with state-of-the-art molar mass (MM) characterization. Methylene blue (MB) adsorption, antioxidant activity, and glass transition temperature (Tg) were used to demonstrate and compare the properties/performance of the obtained modified lignins. We found that the contribution of different functionalities in the adsorption of MB follows the trend BenzOH > -COOH > AlipOH > PhOH. Noteworthy, benzylic -OH contributes ca. 3 and 2.3 times more than phenolic and aliphatic -OH, respectively. An 11% and 17% increase of Tg was observed with respect to the unmodified Indulin by methylating benzylic -OH groups and through reduction, respectively, while full acetylation/methylation of aliphatic and phenolic -OH groups resulted in lower Tg. nRSI experiments revealed that phenolic -OH play a crucial role in increasing the antioxidant activity of lignin, while both aliphatic -OH groups and -COOHs possess a detrimental effect, most likely due to H-bonding. Overall, for the first time, we provide here a reliable approach for the engineering of lignin-based products in high value applications by disclosing the role of specific lignin functionalities.

Bacterial transformation of lignin: key enzymes and high-value products

Lignin, a natural organic polymer that is recyclable and inexpensive, serves as one of the most abundant green resources in nature. With the increasing consumption of fossil fuels and the deterioration of the environment, the development and utilization of renewable resources have attracted considerable attention. Therefore, the effective and comprehensive utilization of lignin has become an important global research topic, with the goal of environmental protection and economic development. This review focused on the bacteria and enzymes that can bio-transform lignin, focusing on the main ways that lignin can be utilized to produce high-value chemical products. Bacillus has demonstrated the most prominent effect on lignin degradation, with 89% lignin degradation by Bacillus cereus. Furthermore, several bacterial enzymes were discussed that can act on lignin, with the main enzymes consisting of dye-decolorizing peroxidases and laccase. Finally, low-molecular-weight lignin compounds were converted into value-added products through specific reaction pathways. These bacteria and enzymes may become potential candidates for efficient lignin degradation in the future, providing a method for lignin high-value conversion. In addition, the bacterial metabolic pathways convert lignin-derived aromatics into intermediates through the "biological funnel", achieving the biosynthesis of value-added products. The utilization of this "biological funnel" of aromatic compounds may address the heterogeneous issue of the aromatic products obtained via lignin depolymerization. This may also simplify the separation of downstream target products and provide avenues for the commercial application of lignin conversion into high-value products.

Structural elucidation and targeted valorization of untractable lignin from pre-hydrolysis liquor of xylose production via a simple and robust separation approach

Effective separation of lignin macromolecules from the xylose pre-hydrolysates (XPH) during the xylose production, thus optimizing the separation and purification process of xylose, is of great significance for reducing the production costs, achieving the high value-added utilization of lignin and increasing the industrial revenue. In this study, a simple and robust method (pH adjustment) for the separation of lignin from XPH was proposed and systematically compared with the conventional acid-promoted lignin precipitation method. The results showed that the lignin removal ratio (up to 60.34 %) of this simple method was higher than that of the conventional method, and the proposed method eliminated the necessity of heating and specialized equipment, which greatly reduced the separation cost. Meanwhile, this simple method does not destroy the components in XPH (especially xylose), ensuring the yield of the target product. On the other hand, the obtained lignin was nano-scale with less condensed structures, which also possessed small molecular weights with narrow distribution, excellent antioxidant activity (8-14 times higher than commercial antioxidants) and UV protection properties. In conclusion, the proposed simple separation method could effectively separate lignin from XPH at low cost, and the obtained lignin had potential commercial applications, which would further enhance the overall profitability of industrial production.

Boosting photo-induced antimicrobial activity of lignin nanoparticles with curcumin and zinc oxide

Lignin nanoparticles have gained increasing attention as a potential antimicrobial agent due to their biocompatibility, biodegradability, and low toxicity. However, the limited ability of lignin to act as an antibacterial is a major barrier to its widespread use. Thus, it is crucial to develop novel approaches to amplify lignin's biological capabilities in order to promote its effective utilization. In this study, we modified lignin nanoparticles (LNPs) with photo-active curcumin (Cur), zinc oxide (ZnO), or a combination of both to enhance their antimicrobial properties. The successful modifications of LNPs were confirmed using comprehensive characterization techniques. The antimicrobial efficacy of the modified LNPs was assessed against both gram-positive and gram-negative bacterial strains. The results showed that the modification of LNPs with Cur and ZnO have much higher antibacterial and antibiofilm activities than unmodified LNPs. Moreover, photo illumination resulted in even higher antibacterial activity. Furthermore, atomic force microscopy revealed bacterial cells lysis and membrane damage by ZnO/Cur modified LNPs. Our research demonstrates that ZnO/Cur modified LNPs can serve as novel hybrid materials with enhanced antimicrobial capabilities. In addition, the photo-induced enhancement in antibacterial activity not only demonstrated the versatility of this hybrid material but also opened up interesting potential for bioinspired therapeutics agents.

Enhanced dewaterability of sewage sludge by grafted cationic lignin-based flocculants

Lignin-based flocculants are widely used for wastewater purification, but their application in sludge dewatering has not yet been documented. In this study, a novel cationic lignin-based flocculant named LS-g-CPA was prepared by grafting cationic polyacrylamide (CPA) synthesized from methacryloyloxy ethyltrimethyl ammonium chloride (DMC) and acrylamide (AM) onto sodium lignosulfonate (LS), and its roles and underlying mechanisms in sludge conditioning were investigated. The results showed that LS-g-CPA effectively improved the dewaterability of sludge, reducing the filtration resistance and filter cake moisture content of sludge from 0.61 ± 0.05 × 1012 m/kg to 0.14 ± 0.02 × 1012 m/kg and 85.64 ± 0.25 % to 76.84 ± 0.41 %, respectively. The dewatering performance of LS-g-CPA was positively correlated with the DMC/AM ratio. The quaternary ammonium groups brought by DMC disrupted the reticular structure of extracellular polymeric substances, exposing hydrophobic residues and releasing bound water. Nevertheless, the key to LS-g-CPA for improving sludge dewatering lies more in the amphoteric flocculant properties that enhance sludge flocculation and the octopus-type structure that provides good drainage channels. This study reveals that lignin-based flocculants are effective in improving the dewaterability of sludge, which provides direct evidence for their application in sludge dewatering.

Acute penetrating injury of the spinal cord by a wooden spike with delayed surgery: a case report

Rarely, penetrating injuries to the spinal cord result from wooden objects, creating unique challenges to mitigate neurological injury and high rates of infection and foreign body reactions. We report a man who sustained a penetrating cervical spinal cord injury from a sharpened stick. While initially tetraparetic, he rapidly recovered function. The risks of neurological deterioration during surgical removal made the patient reluctant to consent to surgery despite the impalement of the spinal cord. A repeat MRI on day 3 showed an extension of edema indicating progressive inflammation. On the 7^th day after injury, fever and paresthesias occurred with a large increase in serum inflammatory indicators, and the patient agreed to undergo surgical removal of the wooden object. We discuss the management nuances related to wood, the longitudinal evolution of MRI findings, infection risk, surgical risk mitigation and technique, an inflammatory marker profile, long-term recovery, and the surprisingly minimal neurological deficits associated with low-velocity midline spinal cord injuries. The patient had an excellent clinical outcome. The main lessons are that a wooden penetrating central nervous system injury has a high risk for infection, and that surgical removal from the spinal cord should be performed soon after injury and under direct visualization.

Ductile, High-Lignin-Content Thermoset Films and Coatings

In the context of transitioning toward a more sustainable use of natural resources, the application of lignin to substitute commonly utilized petroleum-based plastics can play a key role. Although lignin is highly available at low cost and presents interesting properties, such as antioxidant and UV barrier activities, its application is limited by its low reactivity, which is a consequence of harsh conditions normally used to extract lignin from biomass. In this work, the use of glyoxylic acid lignin (GA lignin), rich in carboxylic acid groups and hence highly reactive toward epoxy cross-linkers, is presented. GA lignin, which is directly extracted from biomass via a one-step aldehyde-assisted fractionation process, allowed the preparation of thermoset films and coatings via a simple reaction with sustainable poly(ethylene glycol) diglycidyl ether and glycerol diglycidyl ether cross-linkers. This allows one to prepare freestanding films containing up to 70 wt % lignin with tunable mechanical properties and covalently surface-attached coatings containing up to 90 wt % lignin with high solvent resistance. Both films and coatings display antioxidant properties and combine excellent UV barrier activity with high visible transparency, which is attractive for applications in sustainable food packaging.

Recent advances in lignin antioxidant: Antioxidant mechanism, evaluation methods, influence factors and various applications

Lignin, a by-product of processing lignocellulosic materials, has a polyphenolic structure and can be used as an antioxidant directly or synergistically with synthetic types of antioxidants, leading to different applications. Its antioxidant mechanism is mainly related to the production of ROS, but the details need to be further investigated. The antioxidant property of lignin is mainly related to the content of phenolic hydroxyl group, but methoxy, purity will also have an effect on it. In addition, different methods to detect the antioxidant properties of lignin have different advantages and disadvantages. In this paper, the antioxidant mechanism of lignin, the methods to determine the antioxidant activity and the progress of its application in various fields are reviewed. In addition, the current research on the antioxidant properties of lignin and the hot directions are provided, and an outlook on the research into the antioxidant properties of lignin is provided to broaden its potential application areas.

Lignocellulosic Waste Compounds for Pancreatic Lipase Inhibition: Preliminary Extraction by Freon, Obtaining of Proanthocyanidins and Testing on Lipase Activity

The twigs of sea buckthorn, blackcurrant, gooseberries, quince, and grapes were evaluated as a promising source of biologically active compounds-proanthocyanidins (PACs). Sea buckthorn twigs had the highest content of PACs (9.2% on dry biomass). Preliminary pretreatment of biomass with freon R134a did not allow an increase in PACs content in the composition of hydrophilic extract but confirmed the value of freon extract as an antibacterial agent against P. aeruginosa and B. cereus. The content of PACs was used as an indicator for assessment of the influence of hydrophilic extracts on pancreatic lipase activity. Under normal physiological conditions, in the presence of bile, the extract, which contained 42.4% of PACs was more effective compared to the extract which contained 17.5% of PACs. At all concentrations (0.2-40 mg of sample/g of pancreatic lipase), it inhibited lipase activity by 33%. Purified PACs were the most effective in inhibiting lipase activity (by 36%). However, in pathological physiological conditions (without bile), the opposite effect on lipase activity was observed. Thus, PACs and extracts can be used as inhibitors of pancreatic lipase only under normal physiological conditions.

Ethanol organosolv lignin as a substitute for commercial antioxidants, focusing on the structural properties and synergistic effect with myricetin

Lignin has potential as a substitute for natural antioxidants in cosmetics and food industries due to its radical scavenging ability and price competitiveness. The antioxidant activity of lignin depends on its structural properties, and they accordingly have synergy with natural antioxidants. Based on the structural characteristics, the antioxidant activity of ethanol organosolv lignin (EOL) and synergy with myricetin were investigated. The phenolic-OH content was a predominant factor in the antioxidant activity of EOL, and EOL-H with a higher phenolic-OH content and lower IC₅₀ value (0.17 mg/mL) covered a wide synergy range of 1:32-2:1 (EOL:myricetin). The synergistic effect was verified by comparing predicted and actual values based on ESR analysis, and the phenolic-OH ratio (>0.4) of myricetin and EOL for the synergy was suggested. In this respect, the results highlight the potential of lignin with high phenolic-OH content as a substitute for commercial antioxidants with superior activity and broad synergy ranges.

Lignin-based nanomaterials for food and pharmaceutical applications: Recent trends and future outlook

Small particles of size ranging from 1 to 100 nm are referred to as nanoparticles. Nanoparticles have tremendous applications in various sectors, including the areas of food and pharmaceutics. They are being prepared from multiple natural sources widely. Lignin is one such source that deserves special mention due to its ecological compatibility, accessibility, abundance, and low cost. This amorphous heterogeneous phenolic polymer is the second most abundant molecule in nature after cellulose. Apart from being used as a biofuel source, lignin is less explored for its potential at a nano-level. In plants, lignin exhibits cross-linking structures with cellulose and hemicellulose. Numerous advancements have taken place in synthesizing nanolignins for manufacturing lignin-based materials to benefit from the untapped potential of lignin in high-value-added applications. Lignin and lignin-based nanoparticles have numerous applications, but in this review, we are mainly focusing on the applications in the food and pharmaceutical sectors. The exercise we undertake has great relevance as it helps scientists and industries gain valuable insights into lignin's capabilities and exploit its physical and chemical properties to facilitate the development of future lignin-based materials. We have summarized the available lignin resources and their potential in the food and pharmaceutical industries at various levels. This review attempts to understand various methods adopted for the preparation of nanolignin. Furthermore, the unique properties of nano-lignin-based materials and their applications in fields including the packaging industry, emulsions, nutrient delivery, drug delivery hydrogels, tissue engineering, and biomedical applications were well-discussed.

Current roles of lignin for the agroindustry: Applications, challenges, and opportunities

Lignin has the potential to be used as an additive, coating agent, fertilizer, plant growth stimulator, and packaging material in the agroindustry due to its functional aromatic structure. The quantitative measurement of functional groups is a significant element of the research for lignin structure since they directly impact their optical, dispersion, and chemical properties. These physical and chemical properties of lignin strongly depend on its type and source and its isolation procedure. Thus, lignin provides numerous opportunities for the circular economy in the agroindustry; however, studying and resolving the challenges associated with its separation, purification, and modification is required. This review discusses the most recent findings on lignin use in agroindustry and historical facts about lignin. The properties of lignin and its roles as coating agents, pesticide carriers, plant growth stimulators, and soil-improving agents have been summarized. The emerging challenges in the field of lignin-based agroindustry are considered, and potential future steps to overcome these challenges are discussed.

From sugarcane to skin: Lignin as a multifunctional ingredient for cosmetic application

Lignin has been suggested as a promising candidate for cosmetic applications due to its remarkable potential to absorb ultraviolet rays and distinctive antioxidant activity. This study aims at evaluating the performance of lignin from sugarcane bagasse (SCB) as natural UV blocker, antioxidant, and pigment. Lignin was extracted from SCB, characterized and incorporated into a blemish balm (BB) cream. The biological potential, concretely, in vitro and in vivo sun protection factor (SPF) and in vitro UVA-PF, and safety were assessed. A high-purity SCB lignin (>92 %) was obtained by a mild alkaline extraction process. The results of cytotoxicity, mutagenicity, skin sensitization and in vivo acute cutaneous irritation demonstrated that SCB lignin is safe for topical applications. Lignin showed capacity to scavenge both ABTS and DPPH radicals, which were preserved after its incorporation into the cosmetic formulation. Notable results were achieved in terms of in vitro and in vivo SPF of 9.5 ± 2.9 and 9.6 ± 0.8, respectively. Furthermore, the tested lignin-based BB cream revealed a broad-spectrum UV protection (critical wavelength of 378 ± 0.5 nm). These results suggest SCB lignin as multifunctional and safe ingredient for use in cosmetic products.

Effect of chemically modified lignin addition on the physicochemical properties of PCL nanofibers

In this study, a chemically modified lignin additive was successfully prepared to improve the physicochemical properties of biodegradable polycaprolactone (PCL)-based nanofibers. The molecular weight and surface functional group characteristics of lignin were effectively controlled through a solvent fractionation process using ethanol. Then, PCL-g-lignin was successfully synthesized by using ethanol-fractionated lignin as a platform for the PCL grafting process. Finally, PCL/PCL-g-lignin composite nanofibers were simply prepared by adding PCL-g-lignin to the PCL doping solution and performing a solution blow spinning process. The addition of PCL-g-lignin could dramatically improve the physical and chemical properties of PCL nanofibers, and in particular, the tensile strength (0.28 MPa) increased by approximately 280 % compared to the conventional PCL. In addition, the lignin moiety present in PCL-g-lignin was able to impart UV blocking properties to PCL nanofibers, and as a result, it was possible to effectively suppress the photolysis phenomenon that occurred rapidly in existing PCL nanofibers. Therefore, PCL-g-lignin may be widely used not only as a reinforcing agent of existing biodegradable nanofibers but also as a functional additive for UV protection.

Light-colored lignin extraction by ultrafiltration membrane fractionation for lignin nanoparticles preparation as UV-blocking sunscreen

A wide range of applications are available for kraft lignin (KL). However, the dark color and wide size distribution of KL make it challenging to use in cosmetics and nanoparticle preparation. In this study, we fractionated KL from a paper-making enterprise using ultrafiltration membrane fractionation, and obtained four kinds of lignin with different molecular weights, namely ultrafiltration lignin (UL). Following that, lignin nanoparticles (ULNPs) were formed by self-assembly from four types of UL. Analyzing the UL and ULNP properties, the low molecular weight lignin, such as ULA, exhibited good antioxidant properties (89.47 %, 5 mg/mL), high brightness (ISO% = 7.55), high L^⁎ value (L^⁎ = 72.3) and low polydispersity index (PDI = 1.41). The ULNP showed a narrow size distribution (0.8-1.4 m) and high dispersibility in sunscreen. When ULNP was added to sunscreen with 5 % load, its sun protection factor (SPF) value increased from 14.93 to 63.74. Therefore, this study offered an effective way for the comprehensive utilization of pulping waste KL.

Opportunities and Challenges for Lignin Valorization in Food Packaging, Antimicrobial, and Agricultural Applications

The exploration of renewable resources is essential to help transition toward a more sustainable materials economy. The valorization of lignin can be a key component of this transition. Lignin is an aromatic polymer that constitutes approximately one-third of the total lignocellulosic biomass and is isolated in huge quantities as a waste material of biofuel and paper production. About 98% of the 100 million tons of lignin produced each year is simply burned as low-value fuel, so this renewable polymer is widely available at very low cost. Lignin has valuable properties that make it a promising material for numerous applications, but it is far from being fully exploited. The aim of this Perspective is to highlight opportunities and challenges for the use of lignin-based materials in food packaging, antimicrobial, and agricultural applications. In the first part, the ongoing research and the possible future developments for the use of lignin as an additive to improve mechanical, gas and UV barrier, and antioxidant properties of food packaging items will be treated. Second, the application of lignin as an antimicrobial agent will be discussed to elaborate on the activity of lignin against bacteria, fungi, and viruses. Finally, the use of lignin in agriculture will be presented by focusing on the application of lignin as fertilizer.

Acidic and alkaline deep eutectic solvents (DESs) pretreatment of grapevine: Component analysis, characterization, lignin structural analysis, and antioxidant properties

Deep eutectic solvents (DESs) have been extensively applied to pretreat lignocellulose; however, comparative research on acidic and alkaline DES pretreatment is relatively lacking. Herein, pretreatment of grapevine agricultural by-products with seven DESs were compared in terms of removal of lignin and hemicellulose and component analysis of the pretreated residues. Among the tested DESs, both acidic choline chloride-lactic (CHCl-LA), and alkaline potassium carbonate-ethylene glycol (K₂CO₃-EG) were effective in delignification. Thereafter, the CHCl-LA and K₂CO₃-EG extracted lignin was compared by analyzing their physicochemical structure changes and antioxidant properties. The results showed that the thermal stability, molecular weight, and phenol hydroxyl percentage of CHCl-LA lignin were inferior to K₂CO₃-EG lignin. It was found that the high antioxidant activity of K₂CO₃-EG lignin was mainly attributed to the abundant phenol hydroxyl, guaiacyl (G), and para-hydroxy-phenyl (H). By comparing acidic and alkaline DES pretreatments and their lignin nuances in biorefining, novel insights are derived for the scheduling and selection of DES for lignocellulosic pretreatment.

Electrospray lignin nanoparticles as Pickering emulsions stabilizers with antioxidant activity, UV barrier properties and biological safety

The inherent complexity and large particle size of native-state lignin are the major factors limiting its performance in high value-added materials. To realize the high-value application of lignin, nanotechnology is a promising method. Therefore, we offer a nanomanufacturing approach to produce lignin nanoparticles with uniform size, regular shape and high yield using electrospray. They are efficient in stabilizing oil-in-water (O/W) Pickering emulsions that remain for one month. Lignin has the abilities to demonstrate broad-spectrum UV resistance and green antioxidant properties in advanced materials, taking advantage of its inherent chemical characteristics. In addition, lignin has high safety for topical products according to an in vitro cytotoxicity test. In addition, the nanoparticle concentrations used in the emulsion were as low as 0.1 mg/ml, which maintained UV-resistant ability and overcame traditional lignin-based materials with unfavorable dark colors. Overall, lignin nanoparticles not only act as stabilizers at the water-oil interface but also realize the high functionality of lignin.

Exploring the Potential of Vine Shoots as a Source of Valuable Extracts and Stable Lignin Nanoparticles for Multiple Applications

Large amounts of vine shoots are generated every year during vine pruning. This residue still presents many of the compounds found in the original plant, including low molecular weight phenolic compounds and structural compounds such as cellulose, hemicellulose, and lignin. For wine-producing regions, the challenge is to develop alternatives that will increase the value of this residue. This work proposes the full valorization of vine shoots, focusing on the extraction of lignin by mild acidolysis for the preparation of nanoparticles. The effect of the pretreatment solvents (ethanol/toluene, E/T, and water/ethanol, W/E), on the chemical and structural features of lignin, was evaluated. The chemical analysis suggests similar composition and structure regardless of the pretreatment solvent, although lignin isolated after pretreatment of biomass with E/T showed a higher content of proanthocyanidins (11%) compared with W/E (5%). Lignin nanoparticles (LNPs) presented an average size ranging from 130-200 nm and showed good stability for 30 days. Lignin and LNPs showed excellent antioxidant properties (half maximal inhibitory concentration, IC₅₀ 0.016-0.031 mg/mL) when compared to commercial antioxidants. In addition, extracts resulting from biomass pretreatment showed antioxidant activity, with W/E presenting a lower IC₅₀ (0.170 mg/mL) than E/T (0.270 mg/mL), correlated with the higher polyphenol content of W/E, with (+)-catechin and (-)-epicatechin being the main compounds detected. Overall, this work shows that the pre-treatment of vine shoots with green solvents can yield (i) the production of high-purity lignin samples with antioxidant properties and (ii) phenolic-rich extracts, promoting the integral reuse of this byproduct and contributing to sustainability.