New insights on structure of lignin‐carbohydrate complex from hot water pretreatment liquor

Physical and oxidative stability of flaxseed oil-in-water emulsions prepared by natural lignin-carbohydrate complex

Flaxseed oil, rich in α-linolenic acid, plays a crucial role in various physiological processes. However, its stability presents certain challenges. In this study, the natural lignin-carbohydrate complex (LCC) was used to prepare the physical and oxidative stability of flaxseed oil-in-water emulsions. The LCC was characterized by HPLC, GPC, and FT-IR. The stability of emulsions was evaluated by viscosity, modulus, and micro-morphology changes. Then, the oxidation products were monitored by UV-vis spectrophotometer and HPLC. The results revealed that the high internal phase emulsion (HIPE) was successfully prepared with 2.5 wt% LCC at an oil/water ratio of 75/25 (v/v). Small droplet size (13.361 μm) and high viscosity (36,500 mPa·s) were found even after 30-day storage. Steric interactions of the LCC play a crucial role in ensuring stability, intricately linked to the interfacial properties of the emulsion. Meanwhile, the oxidative stability of α-linolenic acid in the encapsulated flaxseed oil was significantly higher than that in the bulk flaxseed oil. The results revealed that the LCC as a suitable emulsifier opens a new window for the storage of functional lipids rich in polyunsaturated fatty acids.

Differential Studies on the Structure of Lignin-Carbohydrate Complexes (LCC) in Alkali-Extracted Plant Hemicelluloses

Hemicellulose extracted by alkali treatment is of interest because of the advantages of its intact sugar structure and high degree of polymerization. However, the hemicellulose extracted by alkali treatment contained more lignin fragments and the presence of a lignin-carbohydrate complex (LCC), which affected the isolation and purification of hemicellulose and its comprehensive utilization. Therefore, the evaluation of the LCC structure of different types of lignocellulosic resources is of great significance. In this study, the LCC structures of hardwoods and Gramineae were enriched in alkaline systems. Information on the composition, structural proportions, and connection patterns of LCC samples was discussed. The similarities and differences between the LCC structures of different units of raw materials were comparatively studied. The results indicated that the monosaccharide fractions were higher in the LCC of Gramineae compared to hardwoods. The composition of the lignin fraction was dominated by G and S units. The phenyl glycosidic (PhGlc) bond is the predominant LCC linkage under alkali-stabilized conditions. In addition, Gramineae PhGlc types are more numerous compared to hardwoods. The results of the study provide insights into the differences in the chemical composition and structural features of LCC in different plants and provide important guidance for the optimization of the process of purifying hemicellulose.

Extraction of super high-yield lignin-carbohydrate complexes from rice straw without compromising cellulose hydrolysis

Lignin-carbohydrate complexes (LCC) that exhibit both structural advantages of lignin and carbohydrates are promising amphiphilic biopolymers, but the extraction is challenged by its liable chemical bond cleavage between lignin and carbohydrates. This work proposed a facile chemical route to integrating the production of water-insoluble (WIS LCC) and water-soluble LCC (WS LCC) into the emerging deep eutectic solvent (DES) biorefinery at mild conditions. The tailored mechanochemical fractionation process of ball milling assisted aqueous alkaline DES could extract 24.2 % LCC in total, with the co-production of a highly hydrolysable cellulose fraction (98.7 % glucose conversion). The resulting LCC exhibited considerably high contents of β-O-4, phenyl glycoside, and ferulic acid linkage bonds. When 100 g starting straw was subjected to this technique route, 9.1 g WIS LCC, 15.1 g WS LCC and 45.5 g glucose were cascaded produced. It was proposed that the selective disruption of hydrogen bonding entangled network and the quasi-state dissolution of the whole biomass allowed the subsequent cascade fractionation of WIS LCC, WS LCC and highly hydrolysable cellulose through solution property adjustment. This work showed a promising approach for LCC production with high yield without compromising cellulose conversion potential, which has been challenging in the current lignocellulose biorefinery.

Advanced NMR Characterization of Aquasolv Omni (AqSO) Biorefinery Lignins/Lignin-Carbohydrate Complexes

Our recently reported AquaSolv Omni (AqSO) process shows great potential as a parameter-controlled type of biorefinery, which allows tuning of structure and properties of the products towards their optimal use in high-value applications. Herein, a comprehensive NMR (quantitative 13 C, 31 P, and 2D heteronuclear single-quantum coherence) structural characterization of AqSO lignins is reported. The effect of the process severity (P-factor) and liquid-to-solid ratio (L/S) on the structure of the extracted lignins has been investigated and discussed. Low severity (P-factor in the range 400-600) and L/S=1 led to the isolation of less degraded lignin with a higher β-O-4 content up to 34/100 Ar. Harsher processing conditions (P-factor=1000-2500) yielded more condensed lignins with a high degree of condensation up to 66 at P-factor=2000. New types of lignin moieties, such as alkyl-aryl and alkyl-alkyl chemical bonds together with novel furan oxygenated structures have been identified and quantified for the first time. In addition, the formation of lignin carbohydrate complexes bonds has been hypothesized at low severity and L/S. Based on the obtained data we were able to formulate a possible outlook of the occurring reactions during the hydrothermal treatment. Overall, such detailed structural information bridges the gap from process engineering to sustainable product development.

Structural characterization of lignin-carbohydrate complexes from Chinese quince fruits extracted after enzymatic hydrolysis pretreatment

Chinese quince fruit (CQF) contains abundant pectin; however, the pectin cannot be efficiently separated by conventional approaches because of strong lignin-carbohydrate complexes (LCC). In this study, to elucidate the structural characteristics of the original LCC formed by lignin and pectin in CQF, single and multiple enzymatic hydrolysis pretreatments were innovatively performed, and the resulting LCC preparations were comprehensively characterized using a series of techniques. The enzymatic hydrolysis pretreatments significantly increase the LCC yield, releasing LCC fractions with low molecular weights (Mw = 4660-8288 Da). LCC-4, isolated by pretreatment with cellulase plus xylanase, had the highest galacturonic acid content (15.5 %), followed by LCC-2 (isolated by xylanase pretreatment) of 14.0 %. In CQF, lignin develops lignin-carbohydrate (LC) bonds with pectin to form LCC, with phenyl-glycoside bond being the dominant linkage. Although the pectinase pretreatment reduced the pectin content, signals of the LC linkages in the 2D-HSQC spectra were enhanced. LCC-4 could be considered as the most representative of the original LCC in CQF due to its high pectin content and multiple LCC signals in the 2D-HSQC spectrum. The structural understanding of the original LCC in CQF will lay a foundation for designing appropriate methods for extracting pectin from CQF.

Investigation of chemical linkages between lignin and carbohydrates in cultured poplar cambium tissues via double isotope labeling

Lignin precursor labeled with ¹³C (coniferin-¹³Cα), carbohydrate precursor labeled with D (6,6-D₂-glucose) were put into cambium tissue stripped from a growing poplar. The tissue was further cultured in vitro for 18d. Then, the isotopic abundance was determined. The results showed that the labeled precursors could be normally involved in the formation of new xylem. The labeled new xylem tissue was fractionated by ionic liquid DMSO/TBAH system to obtain two components: glucan-lignin complex (GL) and xylan-lignin complex (XL). The X-ray diffraction (XRD) results indicated that the crystalline form of cellulose in the GL component was transformed from type I to type II after the ionic liquid separation. Then the GL and XL were purified and modified by enzymatic and chemical methods, and their structures were elucidated by nuclear magnetic resonance (NMR) spectroscopy. The results showed that lignin subunits in the cultured tissues were mainly connected by β-5 and β-O-4 linkages, of which the β-O-4 substructure unit predominated. Lignin and carbohydrates were mainly connected by acetal bonds, ether bonds, and ester bonds. Combined with the carbohydrate composition and XRD analysis results, the GL components also confirmed the existence of acetal bonds, ester bonds and ether bonds between lignin and cellulose.

Pharmaceutical applications of lignin-derived chemicals and lignin-based materials: linking lignin source and processing with clinical indication

Lignocellulosic biomass is one of the most abundant bioresources on Earth. Over recent decades, various valorisation techniques have been developed to produce value-added products from the cellulosic and hemicellulosic fractions of this biomass. Lignin is the third major component accounting for 10-30% (w/w). However, it currently remains a largely unused fraction due to its recalcitrance and complex structure. The increase in the global demand for lignocellulosic biomass, for energy and chemical production, is increasing the amount of waste lignin available. Approaches to date for valorizing this renewable but heterogeneous chemical resource have mainly focused on production of materials and fine chemicals. Greater value could be gained by developing higher value pharmaceutical applications which would help to improve integrated biorefinery economics. In this review, different lignin extraction methods, such as organosolv and ionic liquid, and the properties and potential of the extracted chemical building blocks are first summarized with respect to pharmaceutical use. The review then discusses the many recent advances made regarding the medical or therapeutic potential of lignin-derived materials such as antimicrobial, antiviral, and antitumor compounds and in controlled drug delivery. The aim is to draw out the link between the source and the processing of the biomass and potential clinical applications. We then highlight four key areas for future research if therapeutic applications of lignin-derived products are to become commercially viable. These relate to the availability and processing of lignocellulosic biomass, technologies for the purification of specific compounds, enhancements in process yield, and progression to human clinical trials.

High-Quality Natural Fibers from Cotton Stalk Bark via Limited Alkali Penetration and Simultaneous Accelerated Temperature Rise

High-quality cotton stalk fibers that are both fine and have a high breakage strength are extracted via limited alkali penetration in the glycerol solvent and simultaneous accelerated temperature rise by means of microwave-assisted heating. Alkali is widely used in the extraction of cotton stalk fibers. However, alkali molecules in the aqueous phase penetrate easily into the fiber bundles, resulting in a simultaneous degumming between the inner and outer layers of the fiber bundles. In previous reports, the fibers treated in the aqueous phase present a coarse fineness (51.0 dtex) under mild conditions or have a poor breakage strength (2.0 cN/dtex) at elevated temperatures. In this study, glycerol is chosen as a solvent to reduce the penetration of alkali. Simultaneously, the microwave-assisted heating form is adopted to increase the temperature to 170 °C within 22 s. The inhibited alkali penetration and accelerated temperature rise limited the delignification to the outer layer, resulting in fibers with both appropriate fineness (23.8 dtex) and high breakage strength (4.4 cN/dtex). Moreover, the fibers also exhibit a clean surface and large contact angle. In this paper, we detail a new strategy to extract high-quality lignocellulosic fibers that will be suitable for potential reinforcing applications.

Structural changes of lignin-carbohydrate complexes (LCCs) from Chinese quince fruits during the sequential fractionation of pectic and hemicellulosic polysaccharides

Chinese quince (Chaenomeles sinensis) fruits offer a potential source of pectin and hemicellulose. However, the existence of lignin-carbohydrate complexes (LCCs) can negatively impact the extraction of pectin and hemicellulose. In this work, LCCs were sequentially fractionated from Chinese quince during the removal of pectin and hemicellulose. The structures of LCCs were characterized by HPAEC, FT-IR, GPC, Py-GC/MS, TGA and 2D HSQC NMR. The results showed that the carbohydrate content and molecular weight of LCCs was found to be changed significantly after the removal of hemicellulose (KSH). The lignin in Björkman LCCs was found to be linked mainly to galactan and fructan, whereas the lignin LCC-AcOHs was found to be linked mainly to arabinan after the removal of KSH. The isolation of carbonate-soluble pectin (NSP) increased thermal stability of Björkman LCC fraction, however, the isolation of chelator-soluble pectin (CSP) increased the thermal stability of LCC-AcOHs. The S/G ratios of LCC-AcOHs increased and large amounts of S-type lignin released during sequential fractionation of pectin and hemicellulose. These results will be beneficial for understanding the mechanisms of pectin and hemicellulose isolation, thereby facilitating the potential application of Chinese quince as a valuable natural resource for food and other industries.

A one-step deconstruction-separation organosolv fractionation of lignocellulosic biomass using acetone/phenoxyethanol/water ternary solvent system

A novel ternary solvent system for organosolv fractionation of lignocellulosic biomass, named APW process, which is composed of acetone, phenoxyethanol and water with the advantages of monophasic deconstruction and biphasic separation of components was developed. Through fractionation of amorpha as a case study, a monophasic APW solution (acetone/phenoxyethanol/water = 5:11:4, volume ratio) with the best lignin affinity was constructed based on Hansen solubility parameters. According to Taguchi experimental design, the optimal conditions were 130 °C, 70 min, 0.15 M sulfuric acid and 20 LSR. Under optimal conditions, removal of lignin and hemicellulose reached 95.60% and 98.39%, respectively. While 80.48% of cellulose was retained in residue and its digestibility was 80.36%. Then, 83.74% of hemicellulose was recovered from aqueous as sugars, and 35.64% of lignin was recovered by precipitation. Moreover, APW process also have effective fractionation of sugarcane bagasse, corn cob and pine, cellulose and hemicellulose recovery were both over 80%.

Selective removal of lignin with sodium chlorite to improve the quality and antioxidant activity of xylo-oligosaccharides from lignocellulosic biomass

As a key anti-degradation barrier that restricts the biotransformation of lignocellulose, the presence of lignin usually severely affects the quality of the extracted xylo-oligosaccharides (XOS). Herein, this study proposed a practical route to improve the quality and antioxidant activity of XOS extracted from lignocellulosic biomass via selective removal of lignin. The highest delignification of 92.6% was successfully achieved with 8% sodium chlorite at 75°C for 2 h. An ideal hemicellulose sample with a purity of 86.1% was obtained by selective removal of lignin. A high-quality XOS sample with a purity of 96.3%, a yield of 77.4%, and a color value of 814 was obtained by separating and purifying the enzymatic hydrolysate. Antioxidant activity assay showed that the highest radical scavenging activity of XOS was 87.3%. Importantly, this study provide a feasible and effective route for the lignocellulosic biomass utilization strategy based on the selective removal of lignin.

Liquid Hot Water Pretreatment of Lignocellulosic Biomass at Lab and Pilot Scale

Liquid hot water pretreatment is considered to be a promising method for increasing biomass digestibility due to the moderate operational conditions without chemical additions. A necessary step towards the scalability of this pretreatment process is performing pilot plant trials. Upscaling was evaluated with a scaling factor of 500, by using 50 mL in the laboratory and 25 L in a pilot plant batch reactor. Pretreatment times were varied from 30 to 240 min, and temperatures used were 180–188 °C, while applying similar heating profiles at both scales. The initial mass fraction of poplar wood chips ranged from 10% to 16%. Liquid hot water pretreatment at laboratory and pilot scale led to analogous results. The acetic acid analysis of the liquid and solid fractions obtained after pretreatment indicated that complete deacetylation of poplar biomass can be achieved.

Enhancement of Interface between Lignocellulosic Fibers and Polypropylene Matrix via the Structure Alteration of Lignin at Elevated Temperatures

This paper investigated the feasibility of enhancing the interface between lignocellulosic fibers and a polypropylene matrix via structure alteration of lignin at elevated temperatures. Alkali treatment can remove gum substances from lignocellulose fibers effectively at elevated temperatures but easily causes damages to fiber strength. In previous studies on directional delignification of lignocellulosic fibers, loss of fiber strength is avoided but condensation and degradation of lignin are accelerated. So far, few reports have been available on the effect of lignin structures on the interface between fibers and a matrix. In this study, jute fibers with different lignin structures are produced at 100 and 130 °C for reinforcing a polypropylene matrix. The interface between the fibers and matrix is analyzed. The result shows that decrease in aliphatic hydroxyl concentration by 9.5% at 130 °C from 3 to 5 h contributes to a 14.2% decrease in the surface energy of jute fibers. Meanwhile, the polydispersity index of lignin decreases from 1.21 to 1.15. Centralized distribution of lignin molecule-weight and reduction in fiber surface energy improves the interface between the fibers and matrix, which manifests as a 30.8% increase in the impact strength of the composites. Similar improvement is not observed in the composites reinforced with jute fibers at 100 °C, due to the absence of lignin-structure changes. This paper provides a new strategy to improve the interface between lignocellulose fibers and a hydrophobic matrix.

A novel drug delivery system obtained from hydrophobic modified amphiphilic polymers by Maillard reaction

In order to improve the bioavailability of paclitaxel, hemicellulose fractions from hot water pretreatment liquor were the first time to design new amphiphilic polymers through the Maillard reaction. Structural characteristics, emulsifying and drug release behaviors of the amphiphilic polymers were then investigated in detail. Results showed that the amphiphilic polymers with degrees of substitution ranging from 0.31 to 1.65 were obtained by reacting hemicellulose fractions with dodecylamine. Furthermore, the nanometer paclitaxel emusion was successfully preparaed. The amphiphilic polymer provided excellent emulsifying properties and desired storage stability. The average particle sizes of emulsion stayed in the range of 235-266 nm, even after 90 days of storage. Besides, the amphiphilic polymer also proved considerable paclitaxel preservation ability and released performance of pH-responsive. The controlled release of paclitaxel was better at pH 5.0, and thus the new amphiphilic polymer can be used as a delivery carrier of hydrophobic drugs.

Understanding the structural characteristics of water-soluble phenolic compounds from four pretreatments of corn stover and their inhibitory effects on enzymatic hydrolysis and fermentation

BACKGROUND

For bioethanol production from lignocellulosic biomass, phenolics derived from pretreatment have been generally considered as highly inhibitory towards enzymatic hydrolysis and fermentation. As phenolics are produced from lignin degradation during pretreatment, it is likely that the pretreatment will exert a strong impact on the structure of phenolics, resulting in varied levels of inhibition of the bioconversion process. Despite the extensive studies on pretreatment, it remains unclear how pretreatment process affects the properties of generated phenolics and how the inhibitory effect of phenolics from different pretreatment varies on enzymatic hydrolysis and fermentation.

RESULTS

In this study, the structural properties of phenolic compounds derived from four typical pretreatment [dilute acid (DA), liquid hot water pretreatment (LHW), ammonia fiber expansion (AFEX) and alkaline pretreatment (AL)] were characterized, and their effect on both enzymatic hydrolysis and fermentation were evaluated. The inhibitory effect of phenolics on enzymatic hydrolysis followed the order: AFEX > LHW > DA > AL, while the inhibitory effect of phenolics on Zymomonas mobilis 8b strain fermentation followed the order: AL > LHW > DA > AFEX. Interestingly, this study revealed that phenolics derived from AFEX showed more severe inhibitory effect on enzymatic hydrolysis than those from the other pretreatments at the same phenolics concentrations (note: AFEX produced much less amount of phenolics compared to AL and DA), while they exhibited the lowest inhibitory effect on fermentation. The composition of phenolics from different pretreatments was analyzed and model phenolics were applied to explore the reason for this difference. The results suggested that the amide group in phenolics might account for this difference.

CONCLUSIONS

Pretreatment process greatly affects the properties of generated phenolics and the inhibitory effects of phenolics on enzymatic hydrolysis and fermentation. This study provides new insight for further pretreatment modification and hydrolysate detoxification to minimize phenolics-caused inhibition and enhance the efficiency of enzymatic hydrolysis and fermentation.

Comparative Evaluation of Organic Acid Pretreatment of Eucalyptus for Kraft Dissolving Pulp Production

Pretreatment is an essential process for the extensive utilization of lignocellulose materials. The effect of four common organic acid pretreatments for Kraft dissolving pulp production was comparatively investigated. It was found that under acidic conditions, hemicellulose can be effectively removed and more reducing sugars can be recovered. During acetic acid pretreatment, lignin that was dissolved in acetic acid could form a lignin-related film which would alleviate cellulose hydrolysis, while other organic acids caused severe cellulose degradation. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD) were used to characterize the pretreated chips in the process. Lignin droplets were attached to the surface of the treated wood chips according to the SEM results. The FTIR spectrum showed that the lignin peak signal becomes stronger, and the hemicellulose peak signal becomes weaker with acid pretreatment. The XRD spectrum demonstrated that the crystallinity index of the wood chips increased. The acetic acid pretreatment process-assisted Kraft process achieved higher yield (31.66%) and higher α-cellulose (98.28%) than any other organic acid pretreatment. Furthermore, extensive utilization of biomass was evaluated with the acetic acid pretreatment-assisted Kraft process. 43.8% polysaccharide (12.14% reducing sugar and 31.66% dissolving pulp) and 22.24% lignin (0.29% acetic acid lignin and 21.95% sulfate lignin) were recovered during the process. Biomass utilization could reach 66.04%. Acetic acid pretreatment is a promising process for extensive biomass utilization.