Browning reactions of hydroxycinnamic acids and heterocyclic Maillard reaction intermediates - Formation of phenol-containing colorants

Non-enzymatic conversion of phenolic compounds plays an important role during thermal processing of plant-based food such as coffee, cocoa, and peanuts. However, the more prominent Maillard reaction is mainly studied at a mechanistic level for carbohydrates and amino compounds to clarify reactions that contribute to ('classic') melanoidin formation, but the role of phenolic compounds in such reactions is rarely discussed yet. To understand their contribution to non-enzymatic browning, reactions between ubiquitous phenolic acids, such as caffeic acid and ferulic acid, and prominent heterocyclic Maillard intermediates, namely furfural, hydroxymethylfurfural, and pyrrole-2-carbaldehyde were investigated. Following incubation under roasting conditions (220 °C, 0-30 min), heterogenous products were characterized by high-resolution mass spectrometry, and, after isolation, by nuclear magnetic resonance spectroscopy. By this, color precursors were identified, and it was shown that in addition to aromatic electrophilic substitution, nucleophilic and condensation reactions are key mechanisms contributing to the formation of phenol-containing melanoidins.

Harmony in detoxification: Microalgae unleashing the potential of lignocellulosic pretreatment wastewater for resource utilization

Lignocellulosic biomass is a pivotal renewable resource in biorefinery process, requiring pretreatment, primarily chemical pretreatment, for effective depolymerization and subsequent transformation. This process yields solid residue for saccharification and lignocellulosic pretreatment wastewater (LPW), which comprises sugars and inhibitors such as phenols and furans. This study explored the microalgal capacity to treat LPW, focusing on two key hydrolysate inhibitors: furfural and vanillin, which impact the growth of six green microalgae. Chlorella sorokiniana exhibited higher tolerance to furfural and vanillin. However, both inhibitors hindered the growth of C. sorokiniana and disrupted algal photosynthetic system, with vanillin displaying superior inhibition. A synergistic inhibitory effect (Q < 0.85) was observed with furfural and vanillin on algal growth. Furfural transformation to low-toxic furfuryl alcohol was rapid, yet the addition of vanillin hindered this process. Vanillin stimulated carbohydrate accumulation, with 50.48 % observed in the 0.1 g/L furfural + 0.1 g/L vanillin group. Additionally, vanillin enhanced the accumulation of C16: 0 and C18: 2, reaching 21.71 % and 40.36 %, respectively, with 0.1 g/L vanillin. This study proposed a microalgae-based detoxification and resource utilization approach for LPW, enhancing the comprehensive utilization of lignocellulosic components. The observed biomass modifications also suggested potential applications for biofuel production, contributing to the evolving landscape of sustainable biorefinery processes.

Hydrodeoxygenation of furfural to 2-methylfuran over Cu-Co confined by hollow carbon cage catalyst enhanced by optimized charge transfer and alloy structure

Hydrodeoxygenation of furfural over non-noble metal catalyst is an effective route to synthesis 2-methylfuran, but the reaction is often hampered by the low activity and selectivity of the catalyst. Herein, a bimetallic catalyst with CuCo alloy encapsulated in a hollow nitrogen-doped carbon cages (CuCo/NC) are fabricated by using ZIF-67 as a sacrificial template, which exhibited superior catalytic performance and a full conversion of furfural with a 95.7 % selectivity towards 2-methylfuran was achieved at an under relatively mild reaction conditions (150 ℃, 1.5 MPa H2 and 4.0 h). The characterizations and density functional theory calculations clearly evidenced that the introduced Cu species acts as a switch to regulate the activity and selectivity of the catalyst via two aspects. On the one hand, the Cu species perturb the Co electronic structure leading to adsorption configuration of furfural change from flat to vertical on the catalyst surface, which successfully hindered the hydrogenation of furan ring, resulting high selectivity towards 2-methylfuran. On the other hand, the formed CuCo (111) sites promotes the dissociation of hydrogen, cleavage of the CO bond and reduces the diffusion barrier of hydrogen so as to advance the formation of 2-methylfuran. This work may provide a feasible strategy for the design of nanoalloy catalyst for the hydrodeoxygenation of biomass platforms to value-added chemicals.

Acid-catalyzed transformation of orange waste into furfural: the effect of pectin degree of esterification

The transformation of biomasses from agro-industrial waste can significantly impact the production of green chemicals from sustainable resources. Pectin is a biopolymer present in lignocellulosic biomass as Orange Peel Waste (OPW) and has possibilities for making platform compounds such as furfural for sustainable chemistry. In this work, we studied the transformation to furfural of OPW, pectins, and D-galacturonic acid (D-GalA), which is the main component (65 wt%) of pectin. We analyzed pectins with different degrees of esterification (45, 60 and 95 DE) in a one-pot hydrolysis reaction system and studied the differences in depolymerization and dehydration of the carbohydrates. The results show that the production of furfural decreases as the DE value increases. Specifically, low DE values favor the formation of furfural since the decarboxylation reaction is favored over deesterification. Interestingly, the furfural concentration is dependent upon the polysaccharide composition of pentoses and uronic acid. The obtained concentrations of furfural (13 and 14 mmol/L), D-xylose (6.2 and 10 mmol/L), and L-arabinose (2.5 and 2.7 mmol/L) remained the same when the galacturonic acid was fed either as a polymer or a monomer under the same reaction conditions (0.01 M SA, 90 min and 433 K). OPW is proposed as a feedstock in a biorefinery, in which on a per kg OPW dry basis, 90 g of pectin and 15 g of furfural were produced in the most favorable case. We conclude that the co-production of pectin and furfural from OPW is economically feasible.

Tandem hydrogenation/hydrogenolysis of furfural to 2-methylfuran over multifunctional metallic Cu nanoparticles supported ZIF-8 catalyst

Catalytic transfer hydrogenation (CTH), that employs protic solvents as hydrogen sources to alleviate the use of molecular hydrogen H2, has gained great attention. This work, reports multifunctional, metallic Cu nanoparticles supported ZIF-8 material for CTH of furfural to a highly valued fuel additive, 2-methylfuran (2-MF) using 2-propanol. Of all as-synthesized xCu(yM)/ZIF-8 catalysts with varied NaBH4 concentration (yM) and Cu loading (x), 11Cu(1.5 M)/ZIF-8 exhibited higher catalytic activity with > 99 % FAL conversion and 93.9 % 2-MF selectivity. This is ascribed to its high specific surface area, and existence of optimum amount of Lewis acid-base sites along with Cu0 species, which are responsible for hydrogenation of furfural to furfuryl alcohol and subsequent hydrogenolysis to produce 2-MF. The present work reports a highly efficient and stable, metal-MOF hybrid material for CTH of FAL to 2-MF, which is one among the best reports available in literature, therewith suggests a promising approach for bio-oil upgradation.

Acid-Catalyzed Activation and Condensation of the =C5H Bond of Furfural on Aldehydes, an Entry Point to Biobased Monomers

Furfural is an industrially relevant biobased chemical platform. Unlike classical furan, or C-alkylated furans, which have been previously described in the current literature, the =C5H bond of furfural is unreactive. As a result, on a large scale, C=C and C=O bond hydrogenation/hydrogenolysis is mainly performed, with furfuryl alcohol and methyl tetrahydrofuran being the two main downstream chemicals. Here, we show that the derivatization of the -CHO group of furfural restores the reactivity of its =C5H bond, thus permitting its double condensation on various alkyl aldehydes. Overcoming the recalcitrance of the =C5H bond of furfural has opened an access to a biobased monomer, whose potential have been investigated in the fabrication of renewably-sourced poly(silylether). By means of a combined theoretical-experimental study, a reactivity scale for furfural and its protected derivatives against carbonylated compounds has been established using an electrophilicity descriptor, a means to predict the molecular diversity and complexity this pathway may support, and also to de-risk any project related to this topic. Finally, by using performance criteria for industrial operations in the field of fuels and commodities, we discussed the industrial potential of this work in terms of cost, E-factor, reactor productivity and catalyst consumption.

Furfural to Cyclopentanone - a Search for Putative Oligomeric By-products

We report here on the reductive rearrangement of biomass-derived furfural to cyclopentanone, a promising non-fossil feedstock for fuels and chemicals. An underreported aspect of this reaction is the inevitable formation of heavy byproducts. To mitigate its formation, process condition such as, solvent, catalyst, temperature, acidity, and feed concentration were varied to unravel the chemistry and improve the reaction performance. Water medium was confirmed to play a crucial role, as organic solvents were unable to deliver cyclopentanone or heavy by products. Copper-based catalyst showed the highest selectivity for ring-rearrangement, reaching 50 mol % under the conditions investigated. The main factor influencing the yields of cyclopentanone (CPO), and promote oligomer formation, are the feed concentration and the pH, as high feed concentrations and high acidity facilitate the self-polymerization of furfuryl alcohol (FALC). This was confirmed by dedicated experiments using FALC and the hydroxypentenone intermediate as feed. The concentration challenge could be mitigated by slowly dosing the feed, which increased the desired product yields by 4-12 mol %. Nevertheless, most oligomers appeared to fall in the range of common liquid fuels and could be converted to diesel by hydrodeoxygenation.

Lignocellulosic biomass pretreatment with a lignin stabilization strategy and valorization toward multipurpose fractionation

Lignocellulosic biomass has emerged as a promising alternative with sustainable advantages for the production of a wide range of renewable products and value-added chemicals. In this study, a pretreatment strategy that use a fully recyclable acid hydrotrope (p-TsOH aqueous solution) to extract lignin and employ glyoxylic acid (GA) to stabilize lignin was proposed for biomass valorization toward multipurpose fractionation. 83.0 % of lignin was dissolved out by p-TsOH hydrotrope (80 wt%) with GA addition to form GA-stabilized product at 80 o C for 15 min. The stabilized lignin was subsequently used as an additive in the preparation of lignin-based suncream. Notably, the incorporation of 4 wt% lignin nanospheres into an SPF15 sunscreen yielded a measured SPF of 59.94. Furthermore, the depolymerization of uncondensed lignin into aromatic monomers yielded a high lignin-oil yield of 84.2 %. Additionally, direct heating of the pretreatment liquor facilitated the conversion of monosaccharides into furfural, achieving a desired yield of 53.7 % without the addition of any acid catalyst. The pretreatment also enhanced the enzymatic hydrolysis of glucan, resulting in a saccharification yield of 98.4 %. Moreover, short-term ultrasonication of the pretreated substrate yielded pulp suitable for papermaking. Incorporating 15 wt% fibers into the produced paper sheets led to a 5.3 % increase in tear index and a 25.4 % increase in tensile index. This study presents a viable pretreatment strategy for the multipurpose fractionation of lignocellulosic biomass, offering potential avenues for biomass valorization.

Innovative parallel synthesis of 5-nonanone and furfural from lignocellulosic biomass accompanied by deep economic analysis

An integrated strategy is developed to utilize all three primary components (cellulose, hemicellulose, and lignin) of lignocellulosic biomass for the coproduction of hydrocarbon fuel (5-nonanone) and bio-chemicals (furfural and high purity lignin). After biomass fractionation, (1) 5-nonanone is produced with high yield of 89% using cellulose-derived γ-valerolactone (GVL), which can potentially serve as a platform molecule for the production of liquid hydrocarbon fuels for the transportation sector; (2) furfural, a valuable platform chemical, is produced using hemicellulose; and (3) production of high-purity lignin, which can be used to produce carbon foams or battery anodes. Separation subsystems are designed to effectively recover the solvents for reuse in the conversion processes, which ultimately improves the economic feasibility of the integrated process, resulting in achieving lower minimum selling price (MSP) of $5.47 GGE-1 for 5-nonanone compared to market price. Heat pump is introduced to perform heat integration, which reduces utility requirements more than 85%. Finally, a wide range of techno-economic analysis is performed to highlight the major cost and technological drivers of the integrated process.

Gas-phase hydrogenation of furfural into value-added chemicals: The critical role of metal-based catalysts

Furfural (FF: aldehyde derivable from lignocellulosic biomass) has been widely recognized as a versatile building block for eco-friendly and sustainable applications to reduce industrial reliance on fossil-fuel carbon sources. Hydrogenation of FF, in particular, is recognized as one of the most effective routes for producing various value-added chemicals (e.g., furfuryl alcohol and 2-methylfuran). The gas-phase FF hydrogenation reaction offers economic and environmental advantages over its liquid-phase counterpart in conversion efficiency, product selectivity, and kinetics. The operation of the former does not require high hydrogen pressures or hazardous solvents while not generating undesirable by-products (due to reduced selectivity toward the ring-opening reaction). In this context, the utility of noble and non-noble metal catalyst systems has been recognized for their potential to induce effective FF hydrogenation in the gas phase. The present review addresses current understandings and recent developments in research on gas-phase FF hydrogenation and the factors governing the performance of metal-based catalysts (e.g., materials and surface chemistry; conversion efficiency; product selectivity; and the mechanisms, pathways, and kinetics of the associated reactions). Current shortcomings and research avenues are also discussed to help establish a roadmap for future development of the gas-phase FF hydrogenation technology and associated disciplines. Overall, the present review is expected to offer much-needed insights into the scalability of metal-based catalytic systems for efficient FF hydrogenation in the gas phase.

Co-production of 2,5-dihydroxymethylfuran and furfuralcohol from sugarcane bagasse via chemobiocatalytic approach in a sustainable system

2,5-Dihydroxymethylfuran and furfuryl alcohol serve as versatile building-blocks in pharmaceuticals, polymers, and value-added intermediates. To develop an efficient and sustainable method for their production from biomass, a combined approach using deep eutectic solvent Citric acid:Betaine (CTA:BT) for bagasse catalysis and recombinant E. coli SCFD23 for bioreduction of bagasse-derived 5-hydroxymethylfurfural and furfural was devised. Bagasse was effectively transformed into 5-hydroxymethylfurfural (48 mM) and furfural (14 mM) in CTA:BT (8 wt%)-water at 170 °C for 30 min. Bioreduction of 5-hydroxymethylfurfural and furfural by SCFD23 cell co-expressing formate dehydrogenase and NAD(P)H-dependent aldehyde reductase (SsCR) yielded 2,5-dihydroxymethylfuran (90.0 % yield) and furfuryl alcohol (99.0 % yield) in 6 h, using biomass-derived formic acid, xylose and glucose as co-substrates. Molecular docking confirmed the stable binding and reductase activity of SsCR with the biomass-derived 5-hydroxymethylfurfural and furfural. An efficient and eco-friendly chemobiological approach was applied for co-production of 2,5-dihydroxymethylfuran and furfuryl alcohol from biomass in one-pot two-step reaction.

Mechanism and dynamics of Baeyer-Villiger oxidation of furfural to maleic anhydride in presence of H2O2 and Au clusters

CONTEXT

The increasing demand for fuels and chemicals in the world has prompted the exploration of various forms of renewable energy resources. Using C5-based furfural as the platform to replace the fossil energy resources is greatly attractive because of its abundance and environmental friendliness. Here we study the activity, selectivity, and possible reaction pathways for the Baeyer-Villiger oxidation of furfural over small Au clusters using hydrogen peroxide as oxidant. Furfural reacts with hydrogen peroxide in the presence of the catalysts with 93% selectivity towards maleic anhydride. Natural population analysis, frontier molecular orbital analysis, and spectroscopic analysis are used to illustrate the interaction mechanism between C5H4O2, H2O2, and Au. Reaction pathways leading to the formation of maleic anhydride are also explored. The reaction of C5H4O2 with H2O2 in the absence of a catalyst bears a relatively high transition state energy barrier of 2.98 eV for the first step involving absorption of H atom of H2O2 on the -OH group of C5H4O2. This is in agreement with the blank experiment where there were rare oxidation products observed in the absence of the metal cluster catalysts. On the other hand, transition state energies in the presence of the Au metal clusters are lower and the most feasible pathway is where the substrate and H2O2 co-bind on the Au catalyst and H2O2 molecule transfers an oxygen to the substrate, leading to the cleavage of the O-O bond.

METHODS

DFT calculations were done with B3PW91 functional. 6-311G(df, p) basis set was used for C, O, and H and aug-cc-pVDZ-PP was used for gold atoms. Gaussian 09 software was used for the calculations. Multiwfn 3.7 dev was used for the quantum theory of atoms-in-molecules (QTAIM) investigations.

Efficient co-production of xylooligosaccharides, furfural and reducing sugars from yellow bamboo via the pretreatment with biochar-based catalyst

The research on the efficient use of biomass to produce chemical products has received extensive attention. In this work, a novel heterogeneous biocarbon-based heterogeneous catalyst AT-Sn-YB was prepared using yellow bamboo (YB) as a carrier, and its physical properties were proved to be good by various characterization and stability experiments. In the γ-valerolactone/water (3:1, v/v) medium containing 100 mM CuCl2, the use of AT-Sn-YB (3.6 wt%) under 170 °C for 20 min was applied to catalyze YB into furfural (80.3% yield), accompanied with 2.8 g/L xylooligosaccharides. The YB solid residue obtained from treatment was efficiently saccharified to reducing sugars (17.2 g/L). Accordingly, comprehensive understanding of efficiently co-producing xylooligosaccharides, furfural and reducing sugars from YB was demonstrated via the pretreatment with biochar-based catalyst. This study innovatively used a new type of solid acid to complete the efficient co-production of chemical products, and realized the value-added utilization of yellow bamboo.

Chemobiocatalytic transfromation of biomass into furfurylamine with mixed amine donor in an eco-friendly medium

Biobased furfurylamine (FAM) is a versatile platform molecule for producing additives, pharmaceuticals, and pesticides. Recombinant E. coli HNND-AlaDH was created by co-expressing L-alanine dehydrogenase (AlaDH) and mutated Aspergillus terreus ω-transaminase (HNND), aiming to convert furfural (FUR) into FAM using inexpensive L-alanine and isopropylamine as mixed amine donors. In ChCl:FA:OA (10 wt%), pineapple peel, bagasse, barley shell, peanut shell, and corn stalk could be efficiently transformed into FUR under 170 °C for 10 min. Pineapple peel produced a high titer of FUR (183.3 mM). Additionally, the viscosity, surface tension and polarity of ChCl:FA:OA were explored. The biomass-derived FUR was fully transformed to FAM by HNND-AlaDH with amine donor (1:1:1 of L-Ala/isopropylamine/FUR mol/mol/mol) within 300 min. Accordingly, the FAM productivity was 0.58 g/(g xylan in pineapple peel). This chemobiocatalytic strategy established through the combination of chemocatalysis and biocatalysis could be applied to convert renewable biomass into valuable organic amines.

Mechanism of furfural toxicity and metabolic strategies to engineer tolerance in microbial strains

Lignocellulosic biomass represents a carbon neutral cheap and versatile source of carbon which can be converted to biofuels. A pretreatment step is frequently used to make the lignocellulosic carbon bioavailable for microbial metabolism. Dilute acid pretreatment at high temperature and pressure is commonly utilized to efficiently solubilize the pentose fraction by hydrolyzing the hemicellulose fibers and the process results in formation of furans-furfural and 5-hydroxymethyl furfural-and other inhibitors which are detrimental to metabolism. The presence of inhibitors in the medium reduce productivity of microbial biocatalysts and result in increased production costs. Furfural is the key furan inhibitor which acts synergistically along with other inhibitors present in the hydrolysate. In this review, the mode of furfural toxicity on microbial metabolism and metabolic strategies to increase tolerance is discussed. Shared cellular targets between furfural and acetic acid are compared followed by discussing further strategies to engineer tolerance. Finally, the possibility to use furfural as a model inhibitor of dilute acid pretreated lignocellulosic hydrolysate is discussed. The furfural tolerant strains will harbor an efficient lignocellulosic carbon to pyruvate conversion mechanism in presence of stressors in the medium. The pyruvate can be channeled to any metabolite of interest by appropriate modulation of downstream pathway of interest. The aim of this review is to emphasize the use of hydrolysate as a carbon source for bioproduction of biofuels and other compounds of industrial importance.

Discovery of new strains for furfural degradation using adaptive laboratory evolution in Saccharomyces cerevisiae

In industrial production, the excessive discharge of furfural can pose harm to soil microorganisms, aquatic animals and plants, as well as humans. Therefore, it is crucial to develop efficient and cost-effective methods for degrading furfural in the environment. Currently, the use of Saccharomyces cerevisiae for furfural degradation in water has shown effectiveness, but there is a need to explore improved efficiency and tolerance in S. cerevisiae for this purpose. In this study, we isolated and evolved highly efficient furfural degradation strains, namely YBA_08 and F60C. These strains exhibited remarkable capabilities, degrading 59% and 99% furfural in the YPD medium after 72 h of incubation, significantly higher than the 31% achieved by the model strain S288C. Through analysis of the efficient degradation mechanism in the evolutionary strain F60C, we discovered a 326% increase in the total amount of NADH and NADPH. This increase likely promotes faster furfural degradation through intracellular aldehyde reductases. Moreover, the decrease in NADPH content led to a 406% increase in glutathione content at the background level, which protects cells from damage caused by reactive oxygen species. Mutations and differential expression related to cell cycle and cell wall synthesis were observed, enabling cell survival in the presence of furfural and facilitating rapid furfural degradation and growth recovery. Based on these findings, it is speculated that strains YBA_08 and F60C have the potential to contribute to furfural degradation in water and the production of furfuryl alcohol, ethanol, and FDCA in biorefinery processes.

Potential xylose transporters regulated by CreA improved lipid yield and furfural tolerance in oleaginous yeast Saitozyma podzolica zwy-2-3

Lignocellulose's hydrolysate, a significant renewable source, contains xylose and furfural, making it challenging for industrial production of oleaginous yeast. On xylose fermentation with furfural treatment, OE::DN7263 and OE::DN7661 increased lipid yield and furfural tolerance versus WT, while, which of OE::CreA were decreased owing to CreA regulating DN7263 and DN7661 negatively. OE::CreA generated reactive oxygen species (ROS) causing oxidative damage. OE::DN7263, OE::DN7661, and ΔCreA reduced furfural via NADH; while ΔCreA produced less ROS and OE::DN7263, and OE::DN7661 scavenged ROS quickly, minimizing oxidative damage. Overall, CreA knockout increased DN7263 and DN7661 expression to facilitate xylose assimilation, enhancing NADH generation and ROS clearance. Finally, with mixed sugar fermentation, ΔCreA and OE::DN7263's biomass and lipid yield rose without furfural addition, while that of ΔCreA remained higher than WT after furfural treatment. These findings revealed how oleaginous yeast zwy-2-3 resisted furfural stress and indicated ΔCreA and OE::DN7263 might develop into robust industrial chassis strains.

Phenotypic and comparative transcriptomics analysis of RDS1 overexpression reveal tolerance of Saccharomyces cerevisiae to furfural

The yeast Saccharomyces cerevisiae able to tolerate lignocellulose-derived inhibitors like furfural. Yeast strain performance tolerance has been measured by the length of the lag phase for cell growth in response to the furfural inhibitor challenge. The aims of this work were to obtain RDS1 yeast tolerant strain against furfural through overexpression using a method of in vivo homologous recombination. Here, we report that the overexpressing RDS1 recovered more rapidly and displayed a lag phase at about 12 h than its parental strain. Overexpressing RDS1 strain encodes a novel aldehyde reductase with catalytic function for reduction of furfural with NAD(P)H as the co-factor. It displayed the highest specific activity (24.8 U/mg) for furfural reduction using NADH as a cofactor. Fluorescence microscopy revealed improved accumulation of reactive oxygen species resistance to the damaging effects of inhibitor in contrast to the parental. Comparative transcriptomics revealed key genes potentially associated with stress responses to the furfural inhibitor, including specific and multiple functions involving defensive reduction-oxidation reaction process and cell wall response. A significant change in expression level of log2 (fold change >1) was displayed for RDS1 gene in the recombinant strain, which demonstrated that the introduction of RDS1 overexpression promoted the expression level. Such signature expressions differentiated tolerance phenotypes of RDS1 from the innate stress response of its parental strain. Overexpression of the RDS1 gene involving diversified functional categories is accountable for stress tolerance in yeast S. cerevisiae to survive and adapt the furfural during the lag phase.

Valorization of Boehmeria nivea stalk towards multipurpose fractionation: furfural, pulp, and phenolic monomers

BACKGROUND

As one of the most abundant bioresource in nature, the value-added utilization of lignocellulosic biomass is limited due to its inherent stubbornness. Pretreatment is a necessary step to break down the recalcitrance of cell walls and achieve an efficient separation of three main components (cellulose, hemicelluloses, and lignin).

RESULTS

In this study, hemicelluloses and lignin in Boehmeria nivea stalks were selectively extracted with a recyclable acid hydrotrope, an aqueous solution of P-toluenesulfonic acid (p-TsOH). 79.86% of hemicelluloses and 90.24% of lignin were removed under a mild pretreatment condition, C80T80t20, (acid concentration of 80 wt%, pretreatment temperature and time of 80 °C and 20 min, respectively). After ultrasonic treatment for 10 s, the residual cellulose-rich solid was directly converted into pulp. Subsequently, the latter was utilized to produce paper via mixing with softwood pulp. The prepared handsheets with a pulp addition of 15 wt% displayed higher tear strength (8.31 mN m²/g) and tensile strength (8.03 Nm/g) than that of pure softwood pulp. What's more, the hydrolysates of hemicelluloses and the extracted lignin were transformed to furfural and phenolic monomers with yields of 54.67% and 65.3%, respectively.

CONCLUSIONS

The lignocellulosic biomass, Boehmeria nivea stalks, were valorized to pulp, furfural, and phenolic monomers, successfully. And a potential solution of comprehensive utilization of Boehmeria nivea stalks was provided in this paper.

Advances in enzymatic conversion of biomass derived furfural and 5-hydroxymethylfurfural to value-added chemicals and solvents

The progress of versatile chemicals and bio-based fuels using renewable biomass has gained ample importance. Furfural and 5-hydroxymethylfurfural are biomass-derived compounds that serve as the cornerstone for high-value chemicals and have a myriad of industrial applications. Despite the significant research into several chemical processes for furanic platform chemicals conversion, the harsh reaction conditions and toxic by-products render their biological conversion an ideal alternative strategy. Although biological conversion confers an array of advantages, these processes have been reviewed less. This review explicates and evaluates notable improvements in the bioconversion of 5-hydroxymethylfurfural and furfural to comprehend the current developments in the biocatalytic transformation of furan. Enzymatic conversion of HMF and furfural to furanic derivative have been explored, while the latter has substantially overlooked a foretime. This discrepancy was reviewed along with the outlook on the potential usage of 5-hydroxymethylfurfural and furfural for the furan-based value-added products' synthesis.

Effects of sucrose degradation product furfural on cyanidin-3-O-glucoside: Mechanism of action, stability, and identification of products in sugar solutions

Anthocyanins are often affected by the sweetener sucrose during processing, which is closely related to its typical degradation product, furfural (Ff). However, the specific mechanism is unclear. In this study, Ff and cyanidin-3-O-glucoside (C3G) were used to explain the mechanism of the effect. The results showed that Ff destabilized anthocyanins by chemically reacting with C3G to generate three new adducts. Meanwhile, the color of the C3G solution changed from bright red to dark purple, and the value of the color difference (ΔE) increased significantly by 2.69. Furthermore, the new adducts were less stable than C3G and continued to promote the degradation of C3G when they coexisted with it. The above adducts were also detected in sugar solutions supplemented with C3G, and these adducts were more likely to accumulate under light storage conditions. These results provide a theoretical basis for reducing anthocyanin loss in food processing.

Molecular mechanism of engineered Zymomonas mobilis to furfural and acetic acid stress

Acetic acid and furfural (AF) are two major inhibitors of microorganisms during lignocellulosic ethanol production. In our previous study, we successfully engineered Zymomonas mobilis 532 (ZM532) strain by genome shuffling, but the molecular mechanisms of tolerance to inhibitors were still unknown. Therefore, this study investigated the responses of ZM532 and its wild-type Z. mobilis (ZM4) to AF using multi-omics approaches (transcriptomics, genomics, and label free quantitative proteomics). Based on RNA-Seq data, two differentially expressed genes, ZMO_RS02740 (up-regulated) and ZMO_RS06525 (down-regulated) were knocked out and over-expressed through CRISPR-Cas technology to investigate their roles in AF tolerance. Overall, we identified 1865 and 14 novel DEGs in ZM532 and wild-type ZM4. In contrast, 1532 proteins were identified in ZM532 and wild-type ZM4. Among these, we found 96 important genes in ZM532 involving acid resistance mechanisms and survival rates against stressors. Furthermore, our knockout results demonstrated that growth activity and glucose consumption of mutant strains ZM532∆ZMO_RS02740 and ZM4∆ZMO_RS02740 decreased with increased fermentation time from 42 to 55 h and ethanol production up to 58% in ZM532 than that in ZM532∆ZMO_RS02740. Hence, these findings suggest ZMO_RS02740 as a protective strategy for ZM ethanol production under stressful conditions.

A fractionation strategy of cellulose, hemicellulose, and lignin from wheat straw via the biphasic pretreatment for biomass valorization

Developing an environmentally friendly and efficient pretreatment to utilize wheat straw is essential to a sustainable future. An acid biphasic system with 2-methyltetrahydrofuran (2-MeTHF) organic solvent and dilute p-toluenesulfonic acid (p-TsOH) were employed for the simultaneous fractionation of three components. Results showed that the biphasic system had excellent cellulose protection and high removal of hemicellulose and lignin. In detail, Under the optimal conditions (0.1 M p-TsOH, 2-MeTHF: H₂O = 1:1 (v:v), 140 °C, 3 h), mostly cellulose retained in the residues (95.69%), 57.18% of lignin was removed and high yield of hemicellulose-based C5 sugars was achieved (77.49%). In the further process of dehydration of pre-hydrolysate dichloromethane (DCM) as an organic phase, the yield of furfural was 80.07% (170 °C-80 min). The saccharification of residue reached 95.82%. p-TsOH/2-MeTHF/H₂O pretreatment was desirable for high selectivity fractionation. Important chemicals for bioenergy including furfural, monosaccharides and lignin are obtained.

Electrochemically activated persulfate and peroxymonosulfate for furfural removal: optimization using Box-Behnken design

Furfural removal by electrochemically activated peroxydisulfate (E-PS) and peroxymonosulfate (E-PMS) was investigated. The effect of different anodes was investigated for the electrochemical activation of oxidants. Box Behnken Design was applied to determine optimum operating conditions, which were determined as follows; PS concentration: 2.3 mM, applied current: 1.15 A, pH: 3.5, and reaction time: 118.3 min for E-PS process; PMS concentration: 1.8 mM, applied current: 1.05 A, pH: 3.3, and reaction time: 107.8 min for E-PMS process. The results of the study showed that the E-PMS process is more advantageous in terms of the chemical and electricity costs to be used.

Laccases from Pleurotus ostreatus Applied to the Oxidation of Furfuryl Alcohol for the Synthesis of Key Compounds for Polymer Industry

Laccases are oxidative enzymes with high synthetic potential. In this work, their value in biocatalysis is shown through the green and selective oxidation of furfuryl alcohol into furfural with the aid of mediators. The influence of different parameters, such as pH, enzyme/mediator composition, buffer type, cosolvent tolerance, and reaction times, is investigated. Under the optimal conditions, 20 mol % of TEMPO as mediator and 5.8 U mL^-1 of laccases POXC and POXA1b from Pleurotus ostreatus, quantitative production of furfural is attained after 16 h. POXC laccase stands out for its ability to catalyze the reaction at pH 6.5, whereas POXA1b is notable for its high stability. Furfural conversions reach excellent values (95 %) after 72 h using only 5 mol % of TEMPO at 100 mM. Furthermore, furfuryl alcohol bioamination is achieved by employing the amine transaminase from Chromobacterium violaceum, providing furfuryl amine, a key compound for the polymer industry, through a one-pot sequential approach.

Techno-economic analysis of ionic liquid pre-treatment integrated pyrolysis of biomass for co-production of furfural and levoglucosenone

In the current work, a techno-economic analysis of pyrolysis of choline glycinate pre-treated biomass has been presented for the co-production of furfural and levoglucosenone along with hemicellulose, lignin and biochar as other byproducts. The mass balance suggested that the 1800 kg/h dry sugarcane straw biorefinery plant could produce about 260 kg/h furfural and 65 kg/h levoglucosenone. The minimum selling price of furfural and levoglucosenone were also estimated and the values were 1640 and 3590 AU$/tonne at 11.1 % biomass loading with 99 % ionic liquid recycling for furfural and levoglucosenone as the target products, respectively. The base case analysis suggested around 6.9 MAU$ NPV with a payback period of 15.4 years. The sensitivity analysis suggested that biomass loading, ionic liquid recycling and cost, waste heat recovery, furfural yield, interest rate and capital cost are the major influential factors for both the minimum selling price of furfural and levoglucosenone.

Pilot study on production of aviation fuel from catalytic conversion of corn stover

Aviation fuel is high energy density and is usually produced from refinery in petroleum industry. Production of renewable aviation fuel from biomass eases pressure of carbon emission regulation. The operational processes in this study include steam stripping, hydrolysis of residues, condensation reaction unit, autoclave hydrogenation, fixed-bed hydrodeoxygenation, and oil-upgrading unit. The biomass-derived aviation fuel has a low oxygen content of 0.4 %, while its high heat value is 45.5 MJ/kg. The aviation fuel ranges from C8 ∼ C15, and rich in isoparaffins (50.4 %) while the n-paraffins have a selectivity of 12.2 % and other components are cycloparaffins (19.0 %), aromatic hydrocarbons (11.3 %), and alkenes (5.6 %). The mass yield for aviation fuel from corn stover reaches 10.6 %. This pilot study achieved production of aviation fuel from raw biomass corn stover.

Sustainable lignocellulose fractionation by integrating p-toluenesulfonic acid/pentanol pretreatment with mannitol for efficient production of glucose, native-like lignin, and furfural

A new cutting-edge lignocellulose fractionation technology for the co-production of glucose, native-like lignin, and furfural was introduced using mannitol (MT)-assisted p-toluenesulfonic acid/pentanol pretreatment, as an eco-friendly process. The addition of optimized 5% MT in pretreatment enhanced the delignification rate by 29% and enlarged the surface area and biomass porosity by 1.07-1.80 folds. This increased the glucose yield by 45% (from 65.34 to 94.54%) after enzymatic hydrolysis relative to those without MT. The extracted lignin in the organic phase of pretreatment exhibited β-O-4 bonds (61.54/100 Ar) properties of native cellulosic enzyme lignin. Lignin characterization and molecular docking analyses revealed that the hydroxyl tails of MT were incorporated with lignin and formed etherified lignin, which preserved high lignin integrity. The solubilized hemicellulose (96%) in the liquid phase of pretreatment was converted into furfural with a yield of 83.99%. The MT-assisted pretreatment could contribute to a waste-free biorefinery pathway toward a circular bioeconomy.

Insight into the Interaction of Furfural with Metallic Surfaces in the Electrochemical Hydrogenation Process

Electrocatalytic hydrogenation of furfural on metal surfaces has become an important research subject due to the potential of the reaction product 2-methylfuran as a renewable energy resource. Identifying effective determinants in this reaction process requires a thorough investigation of the complex electrode-electrolyte interactions, which considers a variety of the influential components. In this work, in operando electrochemical Raman Spectroscopy and Molecular Dynamics simulations were utilized to investigate different characteristics of the interface layer in the electrocatalytic hydrogenation of furfural. Hereby, the influence of applied potentials, electrode material, and electrolyte composition were investigated in detail. The studied parameters give an insight into furfural's binding situation, molecular orientation, and reaction mechanism.

An efficient chemoenzymatic cascade strategy for transforming biomass into furfurylamine with lobster shell-based chemocatalyst and mutated ω-transaminase biocatalyst in methyl isobutyl ketone-water

To date, an efficient process for manufacturing valuable furan compounds from available renewable resources has gained great attention via a chemoenzymatic route. In this study, a sulfonated tin-loaded heterogeneous catalyst CLUST-Sn-LS using lobster shell as biobased carrier was prepared to convert corncob (75.0 g/L) into furfural (122.5 mM) at 170 °C for 30 min in methyl isobutyl ketone (MIBK)-H₂O biphasic system (2:1, v/v). To improve furfurylamine yield, a novel recombinant E. coli TFTS harboring robust mutant Aspergillus terreus ω-transaminase [hydrophilic threonine (T) at position 130 was site-directed mutated to hydrophobic phenylalanine (F)] was constructed to transform 300-500 mM furfural into furfurylamine (90.1-93.6 % yield) at 30 °C and pH 7.5 in MIBK-H₂O. Corncob was converted to furfurylamine in MIBK-H₂O with a high productivity of 0.461 g furfurylamine/(g xylan). This constructed chemoenzymatic method coupling bio-based chemocatalyst CLUST-Sn-LS and mutant ω-transaminase biocatalyst in a biphasic system could efficiently convert lignocellulose into furfurylamine.

Formation of process contaminants in commercial and homemade deep-fried breadcrumbs

Breading is a culinary technique widespread throughout the world. Deep-frying breaded foods forms a palatable crust but also promotes the formation of compounds of toxicological relevance. The influence of the composition of breadcrumbs on the risk associated with the formation of acrylamide, hydroxymethylfurfural (HMF), and furfural was investigated in a deep-fried breadcrumb coating model. Commercial (CBC) and homemade (HBC) wheat-based breadcrumbs were characterized by the reducing sugars and the asparagine content among other parameters (moisture, pH, and CIELab color). The formation of process contaminants in fried breadcrumbs were not influenced by their initial content, but they were affected by the precursors level. The HMF content was significantly higher (1.4 times) in fried HBC (172 mg/kg) than in CBC (120 mg/kg). By contrast, the acrylamide content was 3 times higher in fried CBC (332 µg/kg) than in HBC (111 µg/kg). Multivariate analysis shows that asparagine is the limiting factor for acrylamide formation, and the reducing sugar content is the main determinant for the formation of furanic compounds. A signal value of 463 µg/kg is proposed for the acrylamide content in the coating of deep-fried breaded foods. The reducing sugars and asparagine content in breadcrumb coatings should be considered when designing breaded foods, thereby reducing the formation and consequently the dietary exposure to these potentially harmful compounds.

Microwave-assisted choline chloride/1,2-propanediol/methyl isobutyl ketone biphasic system for one-pot fractionation and valorization of Eucalyptus biomass

The developing of pretreatment method to break the biomass barrier of lignocellulosic is a challenging task for achieve high value utilization. A fast microwave-assisted choline chloride/1,2-propanediol/methyl isobutyl ketone biphasic system was constructed for pretreating Eucalyptus to the production of furfural and cellulose-rich residues and the extraction of lignin. Results showed that the combination of AlCl₃·6H₂O and HCl had the best catalytic ability for furfural production among the examined catalysts. Under the optimal conditions (140 °C, 15 min, 0.075 M AlCl₃·6H₂O, 0.05 M HCl), the furfural yield of 55.4 %, the glucose yield of 90.3 % and the delignification rate of 92.4 % could be achieved. Moreover, the extracted lignin samples with a low polydispersity (1.55-1.73) and molecular weight (1380-2040 g/mol) are promising to act as precursor for the value-add products processing. These findings demonstrated an ultrafast pretreatment process with excellent results in biomass fractionation and comprehensive utilization of biomass components.

An efficient and sustainable furfurylamine production from biomass-derived furfural by a robust mutant ω-transaminase biocatalyst

Furfurylamine is a key furan-based compound for manufacturing perfumes, fibers, additives, medicines and agrochemicals. It can be obtained by amination of furfural by ω-transaminase (AtAT) from Aspergillus terreus. In this work, site-directed mutant of amino acid residues [Threonine (T) at AT130 was mutated to Methionine (M) and Glutamic acid (E) at AT133 was mutated to Phenylalanine (F)] was used to change in the flexible region of AtAT. The transamination activity and thermostability were significantly improved. In ChCl:MA (30 wt%), furfural (500 mM) was efficiently transformed into furfurylamine (92% yield) with TMEF after 12 h. 101.3 mM of biomass-derived furfural and 129.7 mM of D-xylose-derived furfural were wholly converted into furfurylamine within 5 h, achieving the productivity of 0.465 g furfurylamine/(g xylan in corncob) and 0.302 g furfurylamine/(g D-xylose). This established chemoenzymatic conversion strategy by bridging chemocatalysis and biocatalysis could be utilized in the valorisation of renewable biomass to valuable furans.

New concept for conversion of lignocellulose to ethanol and furfural

Studies on the chemical mechanisms of furfural formation showed the possibility to apply a new differential catalysis of hemicellulose - its depolymerisation and pentose dehydration to furfural. This change led to the increase in furfural yield and essential decrease of cellulose destruction. The lignocellulose residue that remains after the production of furfural may be subjected to enzymatic hydrolysis to glucose and the subsequent fermentation to ethanol. The remaining lignin appeared to be suitable for the production of additional various value-added products including medicinal mushrooms and laccase-containing enzyme complexes. Based on these developments, an innovative concept is proposed for the waste-free use of lignocellulose to obtain various valuable products. KEY POINTS: • New chemical mechanism of furfural production. • New lignocellulose pretreatment does not damage cellulose and lignin. • Lignocellulose may be processed using waste-free technology.

Process design, simulation, and techno-economic analysis of integrated production of furfural and glucose derived from palm oil empty fruit bunches

This study aims to propose a new process design, simulation, and techno-economic analysis of an integrated process plant that produces glucose and furfural from palm oil empty fruit bunches (EFB). In this work, an Aspen Plus-based simulation has been established to develop a process flow diagram of co-production of glucose and furfural along with the mass and energy balances. The plant's economics are analyzed by calculating the fixed capital income (FCI), operating costs, and working capital. In contrast, profitability is determined using cumulative cash flow (CCF), net present value (NPV), and internal rate of return (IRR). The findings show that the production capacity of 10 kilotons per year (ktpy) of glucose and 4.96 ktpy of furfural with a purity of 98.21 and 99.54%-weight, respectively, was achieved in this study. The FCI is calculated as United States Dollar (USD) 20.80 million, while the working and operating expenses are calculated as USD 3.74 million and USD 16.93 million, respectively. This project achieves USD 7.65 million NPV with a positive IRR of 14.25% and a return on investment (ROI) of 22.06%. The present work successfully develops a profitable integrated process plant that is established with future upscaling parameters and key cost drivers. The findings provided in this work offer a platform and motivation for future research on integrated plants in the food, environment, and energy nexus with the co-location principle.

Graphical Abstract

Biochar and wood ash amended anaerobic digestion of hydrothermally pretreated lignocellulosic biomass for biorefinery applications

This study investigated the effect of biochar and wood ash amendment on the anaerobic digestion of hydrothermally pretreated lignocellulosic biomass. Hydrothermal pretreatment was performed on switchgrass at 200, 250, and 300 °C with 0, 30, and 60 min of retention times. The pretreatment method was optimized using the response surface method for enhanced methane production. At the optimum pretreatment (200 °C/0 min retention time), a specific methane yield of 256.9 mL CH4/g volatile solids (VS), corresponding to an increase of 32.8% with respect to the untreated substrate, was obtained. Hydrothermal pretreatment was beneficial for methane production at temperatures lower than 220 °C and retention times shorter than 20 min. At more severe pretreatment conditions than 220°-20 min, sugars were degraded into other products, causing a decrease in the methane yield. The hydrothermal degradation products, i.e., acetic acid, lactic acid, furfural, and hydroxymethylfurfural concentrations, were also measured and modeled. The addition of biochar and wood ash to BMP assays were tested at 2, 9, 16 g/g VSinoculum ratios and <63, 63-125, 125-250 μm particle sizes. A decline in methane production was observed for all tested doses and particle sizes of both additives. The decline in the methane potential was proportional to the doses and particle sizes. Kinetic modeling of BMP test results also supported that using the additives was not beneficial. Based on the result of this study, it was found that the use of biochar and wood ash in a pretreated lignocellulosic biomass processing biorefinery would not be beneficial.

Towards efficient and greener processes for furfural production from biomass: A review of the recent trends

As mentioned in several recent reviews, biomass-based furfural is attracting increasing interest as a feasible alternative for the synthesis of a wide range of non-petroleum-derived compounds. However, the lack of environmentally friendly, cost-effective, and sustainable industrial procedures is still evident. This review describes the chemical and biological routes for furfural production. The mechanisms proposed for the chemical transformation of xylose to furfural are detailed, as are the current advances in the manufacture of furfural from biomass. The main goal is to overview the different ways of improving the furfural synthesis process. A pretreatment process, particularly chemical and physico-chemical, enhances the digestibility of biomass, leading to the production of >70 % of available sugars for the production of valuable products. The combination of heterogeneous (zeolite and polymeric solid) catalyst and biphasic solvent system (water/GVL and water/CPME) is regarded as an attractive approach, affording >75 % furfural yield for over 80 % of selectivity with the possibility of catalyst reuse. Microwave heating as an activation technique reduces reaction time at least tenfold, making the process more sustainable. The state of the art in industrial processes is also discussed. It shows that, when sulfuric acid is used, the furfural yields do not exceed 55 % for temperatures close to 180 °C. However, the MTC process recently achieved an 83 % yield by continuously removing furfural from the liquid phase. Finally, the CIMV process, using a formic acid/acetic acid mixture, has been developed. The economic aspects of furfural production are then addressed. Future research will be needed to investigate scaling-up and biological techniques that produce acceptable yields and productivities to become commercially viable and competitive in furfural production from biomass.

Process design and life cycle assessment of furfural and glucose co-production derived from palm oil empty fruit bunches

In light of environmental issues, lignocellulosic empty fruit bunch (EFB) biomass is promoted as a carbon-neutral, environmentally friendly, and renewable alternative feedstock. A comprehensive environmental assessment of EFB biorefineries is critical for determining their sustainability in parallel with the bioeconomy policy. Nonetheless, no life cycle assessment (LCA) has been performed on co-producing food and biochemicals (furfural and glucose) derived from EFB biomass. This research is the first to evaluate the environmental performance of the furfural and glucose co-production processes from EFB biomass. Environmental analysis is conducted using a prospective gate-to-gate LCA for four impact categories, including global warming potential (GWP), acidification (ADP), eutrophication (EP), and human toxicity (HT). Aspen Plus is used to simulate the co-production process of furfural and glucose as well as generate mass and energy balances for LCA inventory data usage. The findings suggest that the environmental footprint in respect of GWP, ADP, EP, and HT is 4846.85 kg CO2 equivalent per ton EFB, 7.24 kg SO2 equivalent per ton EFB, 1.52 kg PO4 equivalent per ton EFB, and 2.62E-05 kg 1,4-DB equivalent per ton EFB, respectively. The normalized overall impact scores for GWP, ADP, EP, and HT are 1.16E-10, 2.28E-11, 6.12E-10, and 2.18E-17 years/ton of EFB, respectively. In summary, the proposed integrated plant is not only economically profitable but also environmentally sustainable. In the attempt to enhance the Malaysian economic sector based on the EFB, this study has the potential to serve as an indicator of the environmental sustainability of the palm oil industry.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s10668-022-02633-8.

In-situ generation of fluorescent silica nano-aggregates of silatranyl appended furfural Schiff base and its application to the spectrofluorimetric analysis of phenolic brominated flame retardants in aqueous medium

A silatranyl appended furfural Schiff base (Silt-FUR) has been synthesized and characterized by spectroscopic techniques, elemental analysis and mass spectrometry. The dissolution of Silt-FUR in methanol-water (90:10 v/v) results in the formation of fluorescent nano-aggregates due to the hydrolysis of the silatranyl ring. The formation of nano-aggregates has been confirmed by dynamic light scattering, scanning electron microscopy and transmission electron microscopy. The nano-aggregates exhibit quenching of fluorescence in the presence of phenolic brominated flame retardants such as 3,3',5,5'-tetrabromobisphenol A, 2,4-dibromophenol, 2,4,6-tribromophenol, and pentabromophenol. Density-Functional Theory and NMR titration suggest that acid-base pair formation between azomethinic functionality and flame retardants is the main cause of quenching of fluorescent signal as it causes photoinduced electron transfer. Due to the excellent spectrofluorimetric response of Silt-FUR nano-aggregates to detect brominated phenols, a spectrofluorimetric method has been standardized for the quantification of brominated flame retardants. The detection limit for pentabromophenol obtained is 0.432 µM under optimal experimental conditions, and the linear range of the determination is 0.0495-1.35 µM. Thus, the in-situ generation of nano-aggregates offers a user-friendly method for the detection, quantification and extraction of the brominated phenols with exceptionally high sensitivity and selectivity for pentabromophenol.

Removal of lignin and silica from rice straw for enhanced accessibility of holocellulose for the production of high-value chemicals

The intricate nature and rigidity of rice straw, particularly the presence of lignin and silica, hinders the catalytic valorization, consequently decreasing the yield of target products. This study reports the concurrent removal of lignin and silica from rice straw to obtain enriched holocellulose, then transforming it to furfural (FUR) and levulinic acid (LA). Interestingly, rice straw in the form of powder displays an improved removal of lignin (51.0%) and silica (92.0%) during ammonia treatment. Encouragingly, adding organic solvents, such as THF, to the aqueous system during the pretreatment of rice straw improves the lignin removal to 60.0%. Upon improving lignin removal to 60%, the obtained holocellulose enriched solid residue yields 71.0% FUR along with 52.0% LA, which is 8 and 4-fold higher than what is obtained with parent rice straw, signifying the importance and the prerequisite of lignin and silica removal from rice straw.

Enhanced tolerance of Cupriavidus necator NCIMB 11599 to lignocellulosic derived inhibitors by inserting NAD salvage pathway genes

Polyhydroxybutyrate (PHB) is a bio-based, biodegradable and biocompatible plastic that has the potential to replace petroleum-based plastics. Lignocellulosic biomass is a promising feedstock for industrial fermentation to produce bioproducts such as polyhydroxybutyrate (PHB). However, the pretreatment processes of lignocellulosic biomass lead to the generation of toxic byproducts, such as furfural, 5-HMF, vanillin, and acetate, which affect microbial growth and productivity. In this study, to reduce furfural toxicity during PHB production from lignocellulosic hydrolysates, we genetically engineered Cupriavidus necator NCIMB 11599, by inserting the nicotine amide salvage pathway genes pncB and nadE to increase the NAD(P)H pool. We found that the expression of pncB was the most effective in improving tolerance to inhibitors, cell growth, PHB production and sugar consumption rate. In addition, the engineered strain harboring pncB showed higher PHB production using lignocellulosic hydrolysates than the wild-type strain. Therefore, the application of NAD salvage pathway genes improves the tolerance of Cupriavidus necator to lignocellulosic-derived inhibitors and should be used to optimize PHB production.

Furfural degradation and its effect on Rhodosporidium toruloides-1588 during microbial growth and lipid accumulation

The presence of furfural in the hydrolysates obtained from lignocellulosic biomass sources represents an enormous challenge during their fermentation because furfural is a toxic compound for different microorganisms. Rhodosporidium toruloides-1588 can grow and accumulate lipids using wood hydrolysate as a substrate containing up to 1 g/L of furfural. In this study, the capacity of R. toruloides-1588 to grow and accumulate lipids using furfural without glucose in the media has been observed. R. toruloides-1588 degraded up to 3 g/L of furfural into furfuryl alcohol (1.8 g/L) and 2-furoic acid (0.9 g/L). Furthermore, R. toruloides-1588 accumulated 52% and 30% of its dry weight into lipids using YM media and YM media without glucose, respectively. Fatty acids such as palmitic, stearic and oleic were the most abundant. Finally, R. toruloides-1588 could potentially utilize furfural as a carbon source.

Reductive Carbon-Carbon Coupling on Metal Sites Regulates Photocatalytic CO2 Reduction in Water Using ZnSe Quantum Dots

Colloidal quantum dots (QDs) consisting of precious-metal-free elements show attractive potentials towards solar-driven CO₂ reduction. However, the inhibition of hydrogen (H₂ ) production in aqueous solution remains a challenge. Here, we describe the first example of a carbon-carbon (C-C) coupling reaction to block the competing H₂ evolution in photocatalytic CO₂ reduction in water. In a specific system taking ZnSe QDs as photocatalysts, the introduction of furfural can significantly suppress H₂ evolution leading to CO evolution with a rate of ≈5.3 mmol g^-1  h^-1 and a turnover number (TON) of >7500 under 24 h visible light. Meanwhile, furfural is upgraded to the self-coupling product with a yield of 99.8 % based on the consumption of furfural. Mechanistic insights show that the reductive furfural coupling reaction occurs on surface Zn-sites to consume electrons and protons originally used for H₂ production, while the CO formation pathway at surface anion vacancies from CO₂ remains.

Recent progress in direct production of furfural from lignocellulosic residues and hemicellulose

Furfural is a vital biomass-derived platform molecule, which can be used to synthesize a wide range of value-added chemicals. Furfural and its derivatives are promising alternatives to conventional petroleum chemicals. However, recent industrial production of furfural existed some thorny problems, including low efficiency, energy waste, and environmental pollution. Therefore, tremendous and continuous efforts have been made by researchers to develop novel furfural production processes with high economic viability, production efficiency, and sustainability. This review summarized the merits and shortcomings of disparate catalytic systems for the synthesis of furfural from biomass and biomass pretreatment hydrolysate on the basis of recently published literature. Furthermore, the suggestions for furfural production research were put forward.

A quick and simple paper-based method for detection of furfural and 5-hydroxymethylfurfural in beverages and fruit juices

Improper storage and transportation of non-alcoholic beverages can, over longer periods, induce Maillard reaction, degrading nutritional components and generating genotoxic and carcinogenic by-products such as furfural and 5-hydroxymethylfurfural (HMF), rendering products unsafe for human consumption. Here, we describe a rapid quantitative solution-based method and test-strips for detection of furfural and HMF. The standard spectroscopic method indicated an LOD of 0.006 ± 0.003% (v/v) and 0.005 ± 0.002% (v/v) for furfural and HMF, respectively in fruit juice samples. The novel chromogenic test-strip has sensitivity of 0.008% (v/v) and 0.004% (v/v) for furfural and HMF, respectively in the same samples of fruit juice. Thus, the developed method and test-strips were specific for furfural and HMF and can be used to help ensure food safety and quality in various industrial applications.

Highly efficient conversion of sunflower stalk-hydrolysate to furfural by sunflower stalk residue-derived carbonaceous solid acid in deep eutectic solvent/organic solvent system

Sunflower stalk was utilized as a source of raw material and catalyst for furfural production, and efficient conversion of xylose-rich hydrolysate into furfural was developed in an aqueous deep eutectic solvent/organic solvent medium by carbonaceous solid acid catalyst SO₄^2-/SnO₂-SSXR. The structural characteristics of SO₄^2-/SnO₂-SSXR was characterized by Brunauer-Emmett-Teller (BET), Scanning Electron Microscopy (SEM), Fourier-transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Pyridine Adsorption Fourier-transform Infrared (Py-IR) and Raman. Under the optimum catalytic conditions, furfural (110.1 mM) yield reached 82.6% in a ChCl-MAA/toluene medium at 180 °C in 15 min by 3.6 wt% SO₄^2-/SnO₂-SSXR. Additionally, quite importantly, SO₄^2-/SnO₂-SSXR, ChCl-MAA and toluene had good recyclability for furfural production. The potential catalytic path of xylose dehydration into furfural was proposed by co-catalysis with SO₄^2-/SnO₂-SSXR and ChCl-MAA. This study revealed high potential sustainable application of furfural production.

Co-conversion of wood and polyvinyl chloride to valuable chemicals and high-quality solid fuel

Polyvinyl chloride (PVC)-containing waste streams are difficult to recycle due to high chlorine content in PVC. Toxic dioxins or corrosive hydrogen chloride (HCl) vapor released from improper management of PVC-containing wastes can cause severe environmental pollution and human health problems. While PVC is usually treated as contamination and burden in waste recycling, a novel recycling approach was developed in this study to leverage PVC as an asset. Specifically, red oak and PVC were co-converted in γ-Valerolactone, a green biomass-derivable solvent. During the co-conversion, PVC-derived HCl in the solvent acted as an acid catalyst to produce up to 14.4% levoglucosenone and 14.3% furfural from red oak. On the other hand, dechlorinated PVC hydrocarbons and lignin fraction of red oak reacted each other to form chlorine-free solid fuels with high thermal stability. The higher heating value of the solids was up to 36.2 MJ/kg, which is even higher than the heating value of anthracite coal. After the co-conversion, more than 80% of PVC-contained chlorine turned into chloride ion and the rest formed 5-chlorovaleric acid. 5-chlorovaleric acid crystals were further recovered from the post-reaction liquid with a purity of 91.2%.

Exploration of deep eutectic solvent-based biphasic system for furfural production and enhancing enzymatic hydrolysis: Chemical, topochemical, and morphological changes

Developing a biorefinery process for a highly integrated valorization and fractionation of lignocellulose is crucial for its utilization. Herein, a biphasic system comprising choline chloride/lactic acid and 2-methyltetrahydrofuran with Al₂(SO₄)₃ and H₂SO₄ as catalysts was applied to pretreat Eucalyptus. Results showed that under the optimized conditions (150 °C, 30 min, 0.2 M Al₂(SO₄)₃, 0.075 M H₂SO₄), the furfural yield and enzymatic hydrolysis efficiency could reach 54.7% and 97.0%, respectively. The efficient cellulose conversion was attributed to remarkable removal of lignin (91.0%) and hemicelluloses (100.0%), thereby causing the disruption of cell wall structure and enhancement of cellulose accessibility. Meanwhile, confocal Raman microscope and atomic force microscope displayed that the pretreatment resulted in the decreasing intensities of carbohydrates and lignin different regions of cell walls, and exposing of the embedded microfibers from noncellulosic polymers. Overall, the deep eutectic solvent-based biphasic system displayed high performance for effective utilization of carbohydrate components in lignocellulose.

Catalytic valorization of biomass for furfuryl alcohol by novel deep eutectic solvent-silica chemocatalyst and newly constructed reductase biocatalyst

Chemoenzymatic cascade catalysis using deep eutectic solvent-silica heterogeneous catalyst and reductase biocatalyst was constructed for synthesizing furfuryl alcohol from biomass in one-pot manner. A novel heterogeneous catalyst B:LA-SG(SiO₂) was firstly prepared by immobilizing deep eutectic solvent Betaine:Lactic acid on silica with sol-gel method using tetraethyl orthosilicate as silicon source. High furfural yield (45.3%) was achieved from corncob with B:LA-SG(SiO₂) catalyst (2.5 wt%) in water at 170 ˚C for 0.5 h. Possible catalytic mechanism for converting biomass into furfural was proposed. Moreover, one newly constructed recombinant E. coli KF2021 cells containing formate dehydrogenase and reductase was utilized to transform corncob-valorized furfural into furfuralcohol at 97.7% yield at pH 7.5 and 40 ˚C via HCOONa-driven coenzyme regeneration. Such a hybrid process was constructed for tandem chemocatalysis and biocatalysis in a same reactor, potentially reducing the operation cost, which had potential application for valorization of biomass to value-added furans.

Characteristics and formation mechanism of key volatile compounds in sugar-smoked chicken

In this paper, the volatile compounds and profile of sugar-smoked chicken thighs were studied, which were proceed by using dividual smoking materials such as sucrose, maltose, glucose, fructose and xylose. A total of 33 volatile compounds in sugar-smoked samples were identified and quantitated by gas chromatography/mass spectrometry (GC/MS). The furfural, 5-methylfurfural, 1-octene-3-ol, hexanal, heptanal and nonanal were the most important volatile compounds with odour activity values (OAVs) greater than 1, among which furfural and 5-methylfurfural contributed mainly to the smoky aroma. The sucrose, glucose and fructose pyrolysis all produced high yield of furans, such as furfural (FF) and 5-hydroxymethylfurfural (5-HMF) based on pyrolysis mass spectrometry and gas chromatography/mass spectrometry (Py-GC/MS). During the smoking process, then the 5-HMF pyrolyzed into 5-methylfurfural. The sucrose was the good carbohydrate to form furans with smoky aroma.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13197-021-05071-y.