The potential for oligosaccharide production from the hemicellulose fraction of biomasses through pretreatment processes: xylooligosaccharides (XOS), arabinooligosaccharides (AOS), and mannooligosaccharides (MOS)

Enzymatic production of xylooligosaccharide from lignocellulosic and marine biomass: A review of current progress, challenges, and its applications in food sectors

Over the last decade, xylooligosaccharides (XOS) have attracted great attentions because of their unique chemical properties and excellent prebiotic effects. Among the current strategies for XOS production, enzymatic hydrolysis is preferred due to its green and safe process, simplicity in equipment, and high control of the degrees of polymerization. This paper comprehensively summarizes various lignocellulosic biomass and marine biomass employed in enzymatic production of XOS. The importance and advantages of enzyme immobilization in XOS production are also discussed. Many novel immobilization techniques for xylanase are presented. In addition, bioinformatics techniques for the mining and designing of new xylanase are also described. Moreover, XOS has exhibited great potential applications in the food industry as diverse roles, such as a sugar replacer, a fat replacer, and cryoprotectant. This review systematically summarizes the current research progress on the applications of XOS in food sectors, including beverages, bakery products, dairy products, meat products, aquatic products, food packaging film, wall materials, and others. It is anticipated that this paper will act as a reference for the further development and application of XOS in food sectors and other fields.

Hemicellulose and unlocking potential for sustainable applications in biomedical, packaging, and material sciences: A narrative review

Hemicellulose, a complex polysaccharide abundantly found in plant cell walls, has garnered significant attention for its versatile applications in various fields including biomedical, food packaging, environmental, and material sciences. This review systematically explores the composition, extraction methods, and diverse applications of hemicellulose-derived materials. Various extraction techniques such as organic acid, organic base, enzyme-assisted, and hydrothermal methods are discussed in detail, highlighting their efficacy and potential drawbacks. The applications of hemicellulose encompass biodegradable films, edible coatings, advanced hydrogels, and emulsion stabilizers, each offering unique properties suitable for different industrial needs. Current challenges in hemicellulose research include extraction efficiency, scalability of production processes, and optimization of material properties. Opportunities for future research are outlined, emphasizing the exploration of new applications and interdisciplinary approaches to harness the full potential of hemicellulose. This comprehensive review aims to provide valuable insights for researchers and industry professionals interested in utilizing hemicellulose as a sustainable and functional biomaterial.

Molecular scale behavior of xylan during solvent-controlled extraction and precipitation

Solvent-controlled extraction and precipitation are the most fundamental methods for obtaining hemicellulose from lignocellulosic biomass and purification processes. However, the dissolution and precipitation mechanisms involved have scarcely been mentioned. In this study, the molecular scale behavior of xylan-type hemicellulose during solvent-controlled extraction and precipitation is investigated using molecular dynamics (MD) simulations and density functional theory (DFT) calculations. To bring the model closer to the real extracted xylan, a high degree of polymerization (DP100) of xylan is established, and hemicelluloses with low DP (DP15 and DP50) are also investigated. Four phenomena are explained at the molecular level, including the influence of the polymerization degree and side chain on the solubility of xylan in water, the improvement of the xylan's solubility in NaOH, the precipitation of xylan in ethanol, and the acetyl group preservation of xylan in DMSO. This study contributes to an increased understanding of the dissolution and precipitation mechanisms of hemicellulose and provides a resource for the simulation of high DP hemicellulose, which gives a theoretical basis for the efficient extraction of high-purity hemicellulose as well as economic biorefining.

Bioprocess development for the production of xylooligosaccharide prebiotics from agro-industrial lignocellulosic waste

The development of sustainable biorefineries and bioeconomy has been the mandate of most of the governments with major focus on restricting the climate change concerns and finding new strategies to maintain the global food supply chain. Xylooligosaccharides (XOS) are short-chain oligomers which due to their excellent prebiotic potential in the nutraceutical sector has attracted intense research focus in the recent years. The agro-industrial crop and food waste can be utilized for the production of XOS which are derived from hemicellulose fraction (xylan) of the lignocellulosic materials. The extraction of xylan, is traditionally achieved by acidic and alkaline pretreatments which, however, have limited industrial applications. The inclusion of cutting-edge and environmentally beneficial pretreatment methods and technologies such as deep eutectic solvents and green catalysts are preferred. Moreover, the extraction of xylans from biomass using combinatorial pretreatment approaches may help in economizing the whole bioprocess. The current review outlines the factors involved in the xylan extraction and depolymerization processes from different lignocellulosic biomass and the subsequent enzymatic hydrolysis for XOS production. The different types of oligosaccharides and their prebiotic potential for the growth of healthy gut bacteria have also been explained. The introduction of modern molecular technologies has also made it possible to identify enzymes and microorganisms with the desired characteristics for usage in XOS industrial production processes.

Enhanced hybrid hydrogel based on wheat husk lignin-rich nanocellulose for effective dye removal

Polyvinyl alcohol (PVA) hydrogels were enhanced mechanically through the addition of lignin-rich nanocellulose (LCN), soluble ash (SA) and montmorillonite (MMT) for dye removal. The hybrid hydrogels reinforced with 33.3 wt% of LCN had a 163.0% increase in storage modulus as compared to the PVA/0LCN-33.3SM hydrogel. LCN can be added to the PVA hydrogel to alter its rheological properties. Additionally, hybrid hydrogels were highly efficient in removing methylene blue from wastewater, which was attributed to the synergistic effects of the PVA matrix supporting embedded LCN, MMT, and SA. The adsorption time (0–90 min) showed that the hydrogels containing MMT and SA had high removal efficiency, and the adsorption of methylene blue (MB) by PVA/20LCN-13.3SM was greater than 95.7% at 30°C. It was found that MB efficiency decreased with a high MMT and SA content. Our study provided a new method for the fabrication of polymers-based eco-friendly, low-cost and robust physical hydrogels for the MB removal.

Comparative analysis of two kinds of garlic seedings: qualities and transcriptional landscape

BACKGROUND

Facility cultivation is widely applied to meet the increasing demand for high yield and quality, with light intensity and light quality being major limiting factors. However, how changes in the light environment affect development and quality are unclear in garlic. When garlic seedlings are grown, they can also be exposed to blanching culture conditions of darkness or low-light intensity to ameliorate their appearance and modify their bioactive compounds and flavor.

RESULTS

In this study, we determined the quality and transcriptomes of 14-day-old garlic and blanched garlic seedlings (green seedlings and blanched seedlings) to explore the mechanisms by which seedlings integrate light signals. The findings revealed that blanched garlic seedlings were taller and heavier in fresh weight compared to green garlic seedlings. In addition, the contents of allicin, cellulose, and soluble sugars were higher in the green seedlings. We also identified 3,872 differentially expressed genes between green and blanched garlic seedlings. The Kyoto Encyclopedia of Genes and Genomes analysis suggested enrichment for plant-pathogen interactions, phytohormone signaling, mitogen-activated protein kinase signaling, and other metabolic processes. In functional annotations, pathways related to the growth and formation of the main compounds included phytohormone signaling, cell wall metabolism, allicin biosynthesis, secondary metabolism and MAPK signaling. Accordingly, we identified multiple types of transcription factor genes involved in plant-pathogen interactions, plant phytohormone signaling, and biosynthesis of secondary metabolites among the differentially expressed genes between green and blanched garlic seedlings.

CONCLUSIONS

Blanching culture is one facility cultivation mode that promotes chlorophyll degradation, thus changing the outward appearance of crops, and improves their flavor. The large number of DEGs identified confirmed the difference of the regulatory machinery under two culture system. This study increases our understanding of the regulatory network integrating light and darkness signals in garlic seedlings and provides a useful resource for the genetic manipulation and cultivation of blanched garlic seedlings.

Engineering of xylanases for the development of biotechnologically important characteristics

Xylanases are the main biocatalysts used for the reduction of the xylan backbone from hemicellulose, randomly splitting off β-1,4-glycosidic linkages between xylopyranosyl residues. Xylanase market has been annually estimated at 500 million US Dollars and they are potentially used in broad industrial process ranges such as paper pulp biobleaching, xylo-oligosaccharide production, and biofuel manufacture from lignocellulose. The highly stable xylanases are preferred in the downstream procedure of industrial processes because they can tolerate severe conditions. Almost all native xylanases can not endure adverse conditions thus they are industrially not proper to be utilized. Protein engineering is a powerful technology for developing xylanases, which can effectively work in adverse conditions and can meet requirements for industrial processes. This study considered state-of-the-art strategies of protein engineering for creating the xylanase gene diversity, high-throughput screening systems toward upgraded traits of the xylanases, and the prediction and comprehensive analysis of the target mutations in xylanases by in silico methods. Also, key molecular factors have been elucidated for industrial characteristics (alkaliphilic enhancement, thermal stability, and catalytic performance) of GH11 family xylanases. The present review explores industrial characteristics improved by directed evolution, rational design, and semi-rational design as protein engineering approaches for pulp bleaching process, xylooligosaccharides production, and biorefinery & bioenergy production.

Analysis of Single-Step Pretreatments for Lignocellulosic Platform Isolation as the Basis of Biorefinery Design

Biorefinery feasibility is highly influenced by the early design of the best feedstock transformation pathway to obtain value-added products. Pretreatment has been identified as the critical stage in biorefinery design since proper pretreatment influences subsequent reaction, separation, and purification processes. However, many pretreatment analyses have focused on preserving and valorizing six-carbon sugars for future use in bioconversion processes, leaving aside fractions such as hemicellulose and lignin. To date, there has been no pretreatment systematization for the removal of lignocellulosic fractions. This work defines pretreatment efficacy through operational, economic, environmental, and social indicators. Thus, using the data reported in the literature, as well as the results of the simulation schemes, a multi-criteria weighting of the best-performing schemes for the isolation or removal of cellulose, hemicellulose, and lignin was carried out. As a main result, it was concluded that dilute acid is the most effective for cellulose isolation and hemicellulose removal for producing platform products based on six- and five-carbon sugars, respectively. Additionally, the kraft process is the best methodology for lignin removal and its future use in biorefineries. The results of this work help to elucidate a methodological systematization of the pretreatment efficacy in the design of biorefineries as an early feasibility stage considering sustainability aspects.

Mind the Pulp: Environmental and economic assessment of a sugar beet pulp biorefinery for biobased chemical production

Sugar beet pulp, a byproduct from sugar beet refining, is used by farmers as fertilizer or sold as animal feed. Both options underestimate the potential of sugar beet pulp as a platform to produce specialty and bulky chemicals as a promising pathway for sustainable biochemicals - mind the pulp. This study proposes a biorefinery concept to produce food additives (pectin-derived oligosaccharides) and bulky chemicals (terephthalic acid). Since the biorefinery has a low technology readiness level (TRL = 1), it is relevant to evaluate the feasibility of this biorefinery concept to provide guidance (at an early stage) on the environmental and economic advantages and limitations. For this purpose, the life cycle assessment and techno-economic assessment frameworks are used to assess the environmental impact and economic performance of the biobased terephthalic acid, respectively. Moreover, environmental impacts are accounted for in economic terms using different monetary valuation methods (environmental prices, Ecovalue12, and Ecotax). The environmental impact of biobased terephthalic acid was higher in most impact categories than the fossil counterpart, depending on the selected allocation approach (mass vs economic). The economic feasibility of the proposed biorefinery is highly dependent on the pectin-derived oligosaccharides market price and the valorization of byproducts (humins and levulinic acid). The selection of the monetary valuation method is critical for monetizing environmental impacts when comparing biobased against fossil-based alternatives.

Preparation and nutritional properties of xylooligosaccharide from agricultural and forestry byproducts: A comprehensive review

Xylooligosaccharide (XOS) are functional oligosaccharides with prebiotic activities, which originate from lignocellulosic biomass and have attracted extensive attention from scholars in recent years. This paper summarizes the strategies used in the production of XOS, and introduces the raw materials, preparation methods, and purification technology of XOS. In addition, the biological characteristics and applications of XOS are also presented. The most commonly recommended XOS production strategy is the two-stage method of alkaline pre-treatment and enzymatic hydrolysis; and further purification by membrane filtration to achieve the high yield of XOS is required for prebiotic function. At the same time, new strategies and technologies such as the hydrothermal and steam explosion have been used as pre-treatment methods combined with enzymatic hydrolysis to prepare XOS. XOS have many critical physiological activities, especially in regulating blood glucose, reducing blood lipid, and improving the structure of host intestinal flora.

Extraction, Isolation, and Purification of Value-Added Chemicals from Lignocellulosic Biomass

This review covers the operating conditions for extracting top value-added chemicals, such as levulinic acid, lactic acid, succinic acid, vanillic acid, 3-hydroxypropionic acid, xylitol, 2,5-furandicarboxylic acid, 5-hydroxymethyl furfural, chitosan, 2,3-butanediol, and xylo-oligosaccharides, from common lignocellulosic biomass. Operating principles of novel extraction methods, beyond pretreatments, such as Soxhlet extraction, ultrasound-assisted extraction, and enzymatic extraction, are also presented and reviewed. Post extraction, high-value biochemicals need to be isolated, which is achieved through a combination of one or more isolation and purification steps. The operating principles, as well as a review of isolation methods, such as membrane filtration and liquid–liquid extraction and purification using preparative chromatography, are also discussed.

Characterization of hemicellulose during xylogenesis in rare tree species Castanopsis hystrix

Hemicellulose is an important component of the plant cell wall which vary in structure and composition between plant species. The research of hemicellulose structures is primarily focused on fast-growing plants during xylogenesis, with slow-growing and rare trees receiving the least attention. Here, hemicellulose structure of the rare species Castanopsis hystrix during xylogenesis was analyzed. Acetyl methyl glucuronide xylan was the most common type of hemicellulose in C. hystrix, with a unique tetrasaccharide structure at the reducing end. Hemicellulose type, structure, molecular weight, thermal stability, biosynthesis and acetyl substitution content and pattern remained stable during the xylogenesis in C. hystrix, which could be attributed to its slow growth. The stable polymer type, low side chain modification and high acetyl substitution of hemicellulose throughout the stems are among the reasons for the hardness and corrosion resistance properties of C. hystrix wood. Genetic modification can be used to improve these properties.

RSM-Modeling and Optimization of High Titer Functional Xylo-oligosaccharides Production by Edible Gluconic Acid Catalysis

Xylo-oligosaccharides have great value in food, feed fields. Previous studies have shown that organic acids catalyze the hydrolysis of xylan-rich sources for the production of xylo-oligosaccharides. In this study, gluconic acid of aldonic acid generated xylo-oligosaccharides via hydrolysis of xylan from corncob. In order to maximize efficiency of xylo-oligosaccharides production, the optimum conditions was ascertained by Box-Behnken design-based response surface methodology. The developed process resulted in a maximum xylo-oligosaccharides yield of 57.73% using 4.6% gluconic acid at 167 °C for 28 min, which was similar to the predicted value and fitted models of xylo-oligosaccharides production. The results showed that the reaction temperature was crucial to xylo-oligosaccharides production, and by-product yields (xylose and furfural) could be effectively controlled by both reaction temperature and time. In addition, 44.87 g/L XOS was achieved by decreasing the solid-liquid ratio. Overall, the described process may be a preferred option for future high concentration xylo-oligosaccharides production.

Recent advancements in prebiotic oligomers synthesis via enzymatic hydrolysis of lignocellulosic biomass

Interest in functional food, such as non-digestible prebiotic oligosaccharides is increasing day by day and their production is shifting toward sustainable manufacturing. Due to the presence of high carbohydrate content, lignocellulosic biomass (LCB) is the most-potential, cost-effective and sustainable substrate for production of many useful products, including lignocellulose-derived prebiotic oligosaccharides (LDOs). These have the same worthwhile properties as other common oligosaccharides, such as short chain carbohydrates digestible to the gut flora but not to humans mainly due to their resistance to the low pH and high temperature and their demand is constantly increasing mainly due to increased awareness about their potential health benefits. Despite several advantages over the thermo-chemical route of synthesis, comprehensive and updated information on the conversion of lignocellulosic biomass to prebiotic oligomers via controlled enzymatic saccharification is not available in the literature. Thus, the main objective of this review is to highlight recent advancements in enzymatic synthesis of LDOs, current challenges, and future prospects of sustainably producing prebiotic oligomers via enzymatic hydrolysis of LCB substrates. Enzyme reaction engineering practices, custom-made enzyme preparations, controlled enzymatic hydrolysis, and protein engineering approaches have been discussed with regard to their applications in sustainable synthesis of lignocellulose-derived oligosaccharide prebiotics. An overview of scale-up aspects and market potential of LDOs has also been provided.

Valorization of Chinese hickory shell as novel sources for the efficient production of xylooligosaccharides

Chinese hickory shell, a by-product of the food industry, is still not utilized and urgent to develop sustainable technologies for its valorization. This research focuses on the systematical evaluation of degraded products and xylooligosaccharide production with high yield from the shell via hydrothermal process. The pretreatment was carried out in a bath pressurized reactor at 140-220 °C for 0.5-2 h. The results indicated that the pretreatment condition strongly affected the chemical structures and compositions of the liquid fraction. The maximum yield of XOS (55.3 wt%) with limitation of by-products formation was achieved at 160 °C for 2 h. High temperature (220 °C) and short time (0.5 h) contributed to hydrolysis of xylooligosaccharide with high DP to yield 37.5 wt% xylooligosaccharide with DP from 2 to 6. Xylooligosaccharide obtained mainly consisted of xylan with branches according to the HSQC NMR analysis. Overall, the production of XOS with a high yield from food waste will facilitate the valorization of food waste in the biorefinery industry.

The role of l-arabinose metabolism for Escherichia coli O157:H7 in edible plants

Arabinose is a major plant aldopentose in the form of arabinans complexed in cell wall polysaccharides or glycoproteins (AGP), but comparatively rare as a monosaccharide. l-arabinose is an important bacterial metabolite, accessed by pectolytic micro-organisms such as Pectobacterium atrosepticum via pectin and hemicellulose degrading enzymes. However, not all plant-associated microbes encode cell-wall-degrading enzymes, yet can metabolize l-arabinose, raising questions about their use of and access to the glycan in plants. Therefore, we examined l-arabinose metabolism in the food-borne pathogen Escherichia coli O157:H7 (isolate Sakai) during its colonization of plants. l-arabinose metabolism (araBA) and transport (araF) genes were activated at 18 °C in vitro by l-arabinose and expressed over prolonged periods in planta. Although deletion of araBAD did not impact the colonization ability of E. coli O157:H7 (Sakai) on spinach and lettuce plants (both associated with STEC outbreaks), araA was induced on exposure to spinach cell-wall polysaccharides. Furthermore, debranched and arabinan oligosaccharides induced ara metabolism gene expression in vitro, and stimulated modest proliferation, while immobilized pectin did not. Thus, E. coli O157:H7 (Sakai) can utilize pectin/AGP-derived l-arabinose as a metabolite. Furthermore, it differs fundamentally in ara gene organization, transport and regulation from the related pectinolytic species P. atrosepticum, reflective of distinct plant-associated lifestyles.

MALDI-TOF-MS analysis of hydrolysis products of beechwood and birchwood xylans catalyzed by xylanase from Bacillus subtilis

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was used to analyze the polymerization distribution of xylo-oligosaccharides from birchwood and beechwood xylans following hydrolysis by the xylanase (XynA) from Bacillus subtilis, which was obtained by recombinant expression and purified by Ni2+ affinity column chromatography. The hydrolysis products of birchwood and beechwood xylans were analyzed by thin layer chromatography (TLC) and MALDI-TOF-MS. In the birchwood hydrolysate, the main neutral xylo-oligosaccharides were xylobiose (X2 ) and xylotriose (X3 ), and the acidic xylo-oligosaccharides (polymerization degree 4-12) were attached via a single methyl-glucuronic acid sidechain (MeG). Both X2 and X3 were identified in the beechwood xylan hydrolysate and acidic xylo-oligosaccharides (polymerization degree 4-16), which were structurally similar to those in the birchwood xylan hydrolysate. Therefore, the recombinant xylanase, XynA, has the potential to produce xylobiose (X2 ) and xylotriose (X3 ) as well as acidic xylo-oligosaccharides (MeGXn ) that would be applied in food industry. PRACTICAL APPLICATIONS: Xylo-oligosaccharides are a novel functional food additive, which has great potential in improving the quality of food. Xylo-oligosaccharides with methyl-glucuronic acid sidechains (MeG) are acidic xylo-oligosaccharides (MeGXn), which can be applied in the preparation of drugs for the treatment of cystitis and mucopolysaccharidosis. In this study, xylanase XynA was first obtained by gene cloning and expression and then used to hydrolyze the birchwood and beechwood xylans. The polymerization distribution of xylo-oligosaccharides generated during the enzymatic digestion was then determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Through enzyme hydrolysis, we are able to produce xylobiose and xylotriose for food additives.

Two-stage processing for xylooligosaccharide recovery from rice by-products and evaluation of products: Promotion of lactic acid-producing bacterial growth and food application in a high-pressure process

In this study, we attempted to maximize arabinoxylan conversion into xylooligosaccharide (XOS) from rice husk and rice straw using two saccharification processes and evaluate the promotion of lactic acid-producing bacterial growth, including an investigation of the role of prebiotics in protecting probiotic bacteria in rice drink products in a high-pressure process (HPP). Hydrothermal treatment followed by enzymatic hydrolysis was designed for XOS recovery from rice husk arabinoxylan (RH-AX) and rice straw arabinoxylan (RS-AX). The hydrothermal treatment performed at 170 °C for 20 min and 180 °C for 10 min was the optimal condition to produce XOS liquor from rice husk and rice straw, respectively. Pentopan mono BG successfully recovered XOS from rice husk and rice straw residues at 50 °C, pH 5.5, an enzyme concentration of 50 U and 100 U/g substrate for 24 h. This design converted 92.17 and 88.34% (w/w) of initial RH-AX and RS-AX into saccharides, which comprised 64.01 and 59.52% of the XOS content, respectively. Rice husk xylooligosaccharide (RH-XOS) and rice straw xylooligosaccharide (RS-XOS) had degrees of polymerization ranging from 2 to 6 with some arabino-xylooligosaccharides. RH-XOS and RS-XOS were used to examine the promotion of the growth of lactic acid-producing bacteria strains in the presence of other prebiotics. RH-XOS and RS-XOS strongly promoted the growth of Lactobacillus sakei and Lactobacillus brevis, while other species showed weak to moderate growth. This study represents the first report of the powerful effect of Lactococcus lactis KA-FF1-4 on altering the utilization of XOS but not xylose. Furthermore, for the first time, we reported the capability of XOS to protect probiotics in rice drinks under high-pressure conditions. RH-XOS and RS-XOS resulted in the highest viability of approximately 11 log cfu/mL and exhibited no significant difference compared with the non-HPP treatment. Hence, rice husk and rice straw can be utilized as alternative prebiotic sources that provide biological activity and food applications in the HPP industry.

Efficient biological pretreatment and bioconversion of corn cob by the sequential application of a Bacillus firmus K-1 cellulase-free xylanolytic enzyme and commercial cellulases

We used agricultural residue, corn cob, with biorefinery and bioeconomy concepts. At short-time cultivation in corn cob (12 h), Bacillus firmus K-1 produced cellulase-free xylanolytic enzyme, with xylooligosaccharides (XOSs), X₅ and X₆, as the main products, which can be used in a variety of applications. The xylanolytic enzyme produced from B. firmus K-1 effectively degraded xylan in corn cob, which was examined by chemical composition, scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR). After cultivation, the xylan contained in the corn cob residue was decreased (as biological pretreatment), causing morphological and structural changes, including creating porosity and increasing the surface area and the exposure of cellulose of pretreated corn cob. These results lead to an improvement of cellulose access by cellulases. Commercially available cellulases, Accellerase® 1500 and Cellic® CTec2, yielded significantly higher glucose concentrations from pretreated corn cob compared to untreated corn cob. After saccharification, the lignin-rich corn cob residue can be used as a raw material for other purposes. Moreover, the B. firmus cells, with a low risk to human health, can be used in some applications. This study presents an efficient method for producing high-value-added products from agricultural residue (corn cob) through biological processes which are environmentally friendly and economically viable. KEY POINTS: • High-value-added products were efficiently produced from corn cob by B. firmus K-1. • After biological pretreatment by B. firmus K-1, cellulase can better reach cellulose. • XOSs and cellulose-derived glucose were the main products from corn cob.

Characterization of hemicellulose in Cassava (Manihot esculenta Crantz) stem during xylogenesis

Cassava is one of the three major potato crops due to the high starch content in its tubers. Unlike most current studies on the utilization of cassava tubers, our research is mainly focused on the stem of cassava plant. Through nuclear magnetic resonance (NMR), fourier transform infrared spectrometer (FTIR) and other methods, we found that cassava stalk hemicellulose consists of β-1,4 glycosidic bond-linked xylan backbone with a tetrasaccharide reducing end and decorated with methylated glucuronic acid, acetyl groups and a high degree of arabinose substitutions. Hemicellulose content gradually increased from the upper to the lower parts of the stem. The apical part of cassava stalk contained more branched and heterogeneous glycans than the middle and basal parts, and the molecular weight of hemicellulose increased from top to bottom. Our findings will be helpful in understanding of structural variations of cassava hemicellulose during xylogenesis, as well as in better utilization of cassava plant waste in industry.

In Situ Chemical Locking of Acetates During Xylo-Oligosaccharide Preparation by Lignocellulose Acidolysis

Xylo-oligosaccharides with high value could be obtained by acidolysis of lignocellulosic biomass with acetic acid, which was an urgent problem to solve for the separation of acetic acid from crude xylo-oligosaccharides solution. Four neutralizers, CaCO₃, CaO, Na₂CO₃, and NaOH, were used for in situ chemically locking the acetic acid in the acidolyzed hydrolysate of corncob. The chemically locked hydrolysate was analyzed and compared using vacuum evaporation and spray drying. After CaCO₃, CaO, Na₂CO₃, and NaOH treatment, the locking rates of acetic acid were 92.62%, 94.89%, 95.05%, and 95.58%, respectively, and 39.55 g, 41.13 g, 41.78 g, and 41.87 g of the compound of xylo-oligosaccharide and acetate were obtained. Sodium neutralizer had lesser effect on xylo-oligosaccharide content, and Na₂CO₃ was the best chemical for locking acetic acid among these four neutralizers. This process provides a novel method for effectively utilizing acetic acid during the industrial production of xylo-oligosaccharides via acetic acid.

Enhancement of catalytic performance of a metagenome-derived thermophilic oligosaccharide-specific xylanase by binding module removal and random mutagenesis

Xylo-oligosaccharide (XO) is a promising pre-biotic with applications in food, feed and healthcare products. XO can be produced by enzymatic digestion of xylan with xylanase. In this study, we aimed to improve the biochemical properties relevant to catalysis and kinetics of X11, a thermophilic glycosyl hydrolase (GH) family 11 endo-β-1,4-xylanase derived from a metagenomic library isolated from sugarcane bagasse, under high-temperature conditions preferred for XO synthesis. Removal of a carbohydrate-binding module (X11C) resulted in 6.5 fold greater catalytic efficiency. X11C was further improved by a Pro71Thr mutation in the X11P variant obtained from a random mutagenesis library, which exhibited 15.9 fold greater catalytic efficiency compared with wild-type X11 under the enzyme's optimal conditions of 80°C and pH 6.0. Homology modeling suggested that the improved performance of X11P could be attributed to formation of an extra H-bond between Thr71 and Ser75, which stabilizes the key catalytic residue Glu180 at the active pocket and β-sheet layers and agrees with the respective increase in melting temperature (T_m) where X11P >X11C >X11 as determined by differential scanning fluorimetry. The X11P variant was tested for hydrolysis of beechwood xylan, which showed X6 as the major product followed by X3 and X4 XOs. The highest yield of 5.5 g total XOs product/mg enzyme was observed for X11P, equivalent to 3.7 fold higher than that of wild-type with XO production of >800 mg/g xylan. The X11P enzyme could be developed as a thermophilic biocatalyst for XO synthesis in biorefineries.

An integrated biorefinery process for adding values to corncob in co-production of xylooligosaccharides and glucose starting from pretreatment with gluconic acid

Increasing attention has been paid to the production of high value-added products from lignocellulosic biomass. This study aims to valorize corncob, utilizing it as feedstock for a multi-biorefinery framework, using gluconic acid in the pretreatment. In attempts to maximize yield of xylooligosaccharides, corncob was first subjected to hydrolysis by gluconic acid using response surface methodology, from which the maximum xylooligosaccharides yield of 56.2% was achieved using 0.6 mol/L gluconic acid at 154 °C for 47 min. Results indicated that gluconic acid was an effective solvent for xylooligosaccharides production: a total of 180 g of xylooligosaccharides was obtained from 1 kg corncob as a result of hydrolysis. Moreover, 86.3% conversion of cellulose was achieved from enzymatic hydrolysis of gluconic acid-treated corncob at 10% solids loading. This study presents a strategy for valorizing corncob using it to produce xylooligosaccharides and glucose, which should pave the way for valorizing other agriculture wastes.

Inter domain interactions influence the substrate affinity and hydrolysis product specificity of xylanase from Streptomyces chartreusis L1105

Purpose

This study investigated the influence of inter-domain interactions on the substrate affinity and hydrolysis product specificity of xylanase.

Methods

Genes encoding a GH10 endo-xylanase from Streptomyces chartreusis L1105 xynA and its truncated derivative were cloned and expressed in Escherichia coli. The catalytic activities of the enzyme (xynA) and the derivative xynADCBM, lacking the carbohydrate binding module (CBM), were assessed to evaluate the role of CBM in xynA.

Results

Recombinant xynA (44 kDa) was found to be optimally active on beechwood xylan at 65 °C with pH 7.7, while xynADCBM (34 kDa) exhibited optimal activity at 65 °C with pH 7.2. Additionally, xynA and xynADCBM were found to be highly thermostable at 40–60 °C, each retaining 80% of their original activity after 30 min. The xynADCBM without the CBM domain was highly efficient at hydrolyzing xylan to produce xylobiose (over 67%), which may be because the CBM domain facilitates substrate binding with xylanase. Meanwhile, the xylan hydrolysis efficiency of xynADCBM was higher than that of xynA.

Conclusion

These findings showed that the CBM domain with non-catalytic activity has no significant effect on the characteristics of the enzyme at optimum pH and pH tolerance. It has also been suggested that the derivative xynADCBM without CBM components can promote hydrolysis of xylan to yield xylooligosaccharides, which has great potential economic benefits.

Whey and Its Derivatives for Probiotics, Prebiotics, Synbiotics, and Functional Foods: a Critical Review

The purpose of this review is to highlight the importance of whey as a source of new-generation functional ingredients. Particular interest is given to probiotic growth in the presence of whey derivatives such as lactulose, a lactose derivative, which is a highly sought-after prebiotic in functional feeding. The role of sugar/nitrogen interactions in the formation of Maillard products is also highlighted. These compounds are known for their antioxidant power. The role of bioactive peptides from whey is also discussed in this study. Finally, the importance of an integrated valuation of whey is discussed with an emphasis on functional nutrition and the role of probiotics in the development of novel foods such as synbiotics.

Oligosaccharides from Palm Kernel Cake Enhances Adherence Inhibition and Intracellular Clearance of Salmonella enterica Serovar Enteritidis In Vitro

Salmonella enterica serovar (ser.) Enteritidis (S. Enteritidis) is a foodborne pathogen often associated with contaminated poultry products. This study evaluated the anti-adherence and intracellular clearance capability of oligosaccharides extracted from palm kernel cake (PKC), a by-product of the palm oil industry, and compared its efficacy with commercial prebiotics- fructooligosaccharide (FOS) and mannanoligosaccharide (MOS)-against S. Enteritidis in vitro. Based on the degree of polymerization (DP), PKC oligosaccharides were further divided into 'Small' (DP ≤ 6) and 'Big' (DP > 6) fractions. Results showed that the Small and Big PKC fractions were able to reduce (p < 0.05) S. Enteritidis adherence to Cancer coli-2 (Caco-2) cells at 0.1 mg/ mL while MOS and FOS showed significant reduction at 1.0 mg/mL and 10.0 mg/mL, respectively. In terms of S. Enteritidis clearance, oligosaccharide-treated macrophages showed better S. Enteritidis clearance over time at 50 µg/mL for Small, Big and MOS, while FOS required a concentration of 500 µg/mL for a similar effect. This data highlights that oligosaccharides from PKC, particularly those of lower DP, were more effective than MOS and FOS at reducing S. Enteritidis adherence and enhancing S. Enteritidis clearance in a cell culture model.

Selective deconstruction of hemicellulose and lignin with producing derivatives by sequential pretreatment process for biorefining concept

For improving the economic efficiency of the biorefining concept, selective decomposition and separation of biomass components is indispensable. In this respect, a sequential pretreatment process consisting of liquid hot water treatment and diluted peracetic acid (PAA) treatment was proposed for total utilization of lignocellulosic woody biomass. During the liquid hot water treatment, hemicellulose can be decomposed efficiently without significant loss of cellulose and lignin, implying the possibility for xylooligomer production by thermochemical treatment. In the PAA treatment, lignin was successfully degraded and liquefied using a 50% diluted PAA solvent, suggesting the possibility of dicarboxylic acid production. After the sequential process proposed in this study, the cellulose accessibility to the enzyme could be maximized by inducing selective deconstruction of hemicellulose and lignin.

A novel neutral and thermophilic endoxylanase from Streptomyces ipomoeae efficiently produced xylobiose from agricultural and forestry residues

Endoxylanases capable of producing high ratios of xylobiose from agricultural and forestry residues in neutral and high temperature conditions are attractive for the prebiotic and alternative sweetener industries. In this study, a putative glycosyl hydrolase gene from Streptomyces ipomoeae was cloned and expressed in Escherichia coli. The recombinant enzyme, named as SipoEnXyn10A, hydrolyzed beechwood xylan in endo-action mode releasing xylobiose as its main end product. It was most active at pH 6.5 and 75-80 °C and showed remarkable stability at 65 °C. The xylobiose yield from 10 g corncob and moso bamboo reached 1.123 ± 0.021 and 0.229 ± 0.005 g, respectively, at pH 6.5 and 70 °C, whichwas higher than other reports using the same material. Moreover, high ratios of xylobiose in the xylose-based product of about 85% were obtained from corncob, moso bamboo sawdust, cassava stem and Chinese fir sawdust. These results demonstrated that SipoEnXyn10A has potential for industrial application.

High concentration and yield production of mannose from açaí (Euterpe oleracea Mart.) seeds via mannanase-catalyzed hydrolysis

The açaí seed corresponds to approximately 85% of the fruit's weight and represents ~1.1 million metric tons of residue yearly accumulated in the Amazon region, resulting in an acute environmental and urban problem. To extract the highest value from this residue, this study aimed to evaluate its chemical composition to determine the appropriate applications and to develop conversion methods. First, mannan was confirmed as the major component of mature seeds, corresponding to 80% of the seed's total carbohydrates and about 50% of its dry weight. To convert this high mannan content into mannose, a sequential process of dilute-acid and enzymatic hydrolysis was evaluated. Among different dilute-H2SO4 hydrolysis conditions, 3%-acid for 60-min at 121 °C resulted in a 30% mannan hydrolysis yield and 41.7 g/L of mannose. Because ~70% mannan remained in the seed, a mannanase-catalyzed hydrolysis was sequentially performed with 2-20% seed concentration, reaching 146.3 g/L of mannose and a 96.8% yield with 20% solids. As far as we know, this is the highest reported concentration of mannose produced from a residue. Thus, this work provides fundamental data for achieving high concentrations and yields of mannose from açaí seeds, which could add commercial value to the seeds and improve the whole açaí productive chain.

Lignocellulose derived functional oligosaccharides: production, properties, and health benefits

Lignocellulosic biomass (LB) is the renewable feedstock for the production of fuel/energy, feed/food, chemicals, and materials. LB could also be the versatile source of the functional oligosaccharides, which are non-digestible food ingredients having numerous applications in food, cosmetics, pharmaceutical industries, and others. The burgeoning functional food demand is expected to be more than US$440 billion in 2022. Because of higher stability at low pH and high temperature, oligosaccharides stimulate the growth of prebiotic bifidobacteria and lactic acid bacteria. Xylooligosaccharides (XOS) are major constituents of oligosaccharides consisting of 2-7 xylose monomeric units linked via β-(1,4)-linkages. XOS can be obtained from various agro-residues by thermochemical pretreatment, enzymatic or chemoenzymatic methods. While thermochemical methods are fast, reproducible, enzymatic methods are substrate specific, costly, and produce minimum side products. Enzymatic methods are preferred for the production of food grade and pharmaceutically important oligosaccharides. XOS are potent prebiotics having antioxidant properties and enhance the bio-adsorption of calcium and improving bowel functions, etc. LB can cater to the increasing demand of oligosaccharides because of their foreseeable amount and the advancements in technology to recover oligosaccharides. This paper summarizes the methods for oligosaccharides production from LB, classification, and benefits of oligosaccharides on human health.