Steam explosion and its combinatorial pretreatment refining technology of plant biomass to bio-based products

Enhancing the Hypolipidemic and Functional Properties of Flammulina velutipes Root Dietary Fiber via Steam Explosion

Flammulina velutipes is an edible mushroom widely cultivated in China. As a by-product of Flammulina velutipes, the roots are rich in high-quality dietary fiber (DF). In order to obtain high-quality soluble dietary fiber (SDF), steam explosion (SE) is used as an effective modification method to improve the extraction rate and avoid the loss of active substances. Mounting evidence shows that SDF alleviates lipid metabolism disorders. However, it is not well understood how the influence of SDF with SE pretreatment could benefit lipid metabolism. In this study, we extracted a soluble dietary fiber from Flammulina velutipes root with an SE treatment, named SE-SDF, using enzymatic assisted extraction. The physicochemical and structural properties of the SE-SDF were investigated, and its hypolipidemic effects were also analyzed using oleic-acid-induced HepG2 cells. In addition, the anti-obesity and hypolipidemic effects of SE-SDF were investigated using a high-fat diet (HFD) mouse model. The results indicate that SE treatment (1.0 MPa, 105 s) increased the SDF content to 8.73 ± 0.23%. The SE-SDF was primarily composed of glucose, galactose, and mannose. In HFD-fed mice, SE-SDF significantly reduced weight gain and improved lipid profiles, while restoring liver function and reducing injury. This work provides an effective method for the processing of fungi waste and adds to its economic value. In future studies, the structural characteristics and the anti-obesity and gut microbiota regulation mechanisms of SE-SDF will be explored in depth, supporting its high-value utilization in healthcare products.

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.

Enhancing detoxification of inhibitors in lignocellulosic pretreatment wastewater by bacterial Action: A pathway to improved biomass utilization

The process of preprocessing techniques such as acid and alkali pretreatment in lignocellulosic industry generates substantial solid residues and lignocellulosic pretreatment wastewater (LPW) containing glucose, xylose and toxic byproducts. In this study, furfural and vanillin were selected as model toxic byproducts. Kurthia huakuii as potential strain could tolerate to high concentrations of inhibitors. The results indicated that vanillin exhibited a higher inhibitory effect on K. huakuii (3.95 % inhibition rate at 1 g/L than furfural (0.45 %). However, 0.5 g/L vanillin promoted the bacterial growth (-2.35 % inhibition rate). Interestingly, the combination of furfural and vanillin exhibited antagonistic effects on bacterial growth (Q<0.85). Furfural and vanillin could be bio-transformed into less toxic molecules (furfuryl alcohol, furoic acid, vanillyl alcohol, and vanillic acid) by K. huakuii, and inhibitor degradation rate could be promoted by expression of antioxidant enzymes. This study provides important insights into how bacteria detoxify inhibitors in LPW, potentially enhancing resource utilization.

Extraction and improvement of protein functionality using steam explosion pretreatment: advances, challenges, and perspectives

Protein has become an increasingly valuable food component with high global demand. Consequently, unconventional sources, such as industrial and agroindustrial wastes and by-products, emerge as interesting alternatives to meet this demand, considering the UN Sustainable Development Goals and the transition to a circular economy. In this context, this work presents a review of the use of Steam Explosion (SE), a green technique that can be employed as a pretreatment for various waste materials, including bones, hide/leather, feathers, and wool, aimming the extraction of protein compounds, such as low molecular weight biopeptides, gelatin, and keratin, as well as to enhance the protein functionality of grains and meals. The SE technique and the main factors affecting the process's efficiency were detailed. Promising experimental studies are discussed, along with the mechanisms responsible for protein extraction and functionality improvement, as well as the main reported and suggested applications. In general, steam explosion favored yields in subsequent extraction processes, ranging from 27 to 95%, in addition to enhancing solubility and functional protein properties. Nonetheless, it is crucial to maintain the continuity of research on this topic to drive advancements in ensuring the safety of the extracted compounds for use in consumable products and oral ingestion.

Common operational issues and possible solutions for sustainable biosurfactant production from lignocellulosic feedstock

Surfactants are compounds with high surface activity and emulsifying property. These compounds find application in food, medical, pharmaceutical, and petroleum industries, as well as in agriculture, bioremediation, cleaning, cosmetics, and personal care product formulations. Due to their widespread use and environmental persistence, ensuring biodegradability and sustainability is necessary so as not to harm the environment. Biosurfactants, i.e., surfactants of plant or microbial origin produced from lignocellulosic feedstock, perform better than their petrochemically derived counterparts on the scale of net-carbon-negativity. Although many biosurfactants are commercially available, their high cost of production justifies their application only in expensive pharmaceuticals and cosmetics. Besides, the annual number of new biosurfactant compounds reported is less, compared to that of chemical surfactants. Multiple operational issues persist in the biosurfactant value chain. In this review, we have categorized some of these issues based on their relative position in the value chain - hurdles occurring during planning, upstream processes, production stage, and downstream processes - alongside plausible solutions. Moreover, we have presented the available paths forward for this industry in terms of process development and integrated pretreatment, combining conventional tried-and-tested strategies, such as reactor designing and statistical optimization with cutting-edge technologies including metabolic modeling and artificial intelligence. The development of techno-economically feasible biosurfactant production processes would be instrumental in the complete substitution of petrochemical surfactants, rather than mere supplementation.

Enhanced production of lactic acid from pretreated rice straw using co-cultivation of Bacillus licheniformis and Bacillus sonorenesis

Lactic acid (LA) production from sugar mixture derived from lignocellulosic rice straw employing co- culture system of thermotolerant and inhibitor tolerant Bacillus licheniformis DGB and Bacillus sonorenesis DGS15 was carried out. In minimal media, both the strains of Bacillus DGB and DGS15 worked together by efficiently utilising glucose and xylose respectively. Response Surface Methodology (RSM) was used for optimisation of pretreatment of rice straw to achieve maximum yield of 50.852 g/L total reducing sugar (TRS) from 100 gm of rice straw biomass. Pretreatment of rice straw resulted in its delignification, as confirmed by FTIR spectroscopy, since the peak at 1668 cm-1 disappeared due to removal of lignin and scanning electron microscopy (SEM) revealed disruption in structural and morphological features. Crystallinity index (CrI) of treated rice straw increased by 15.54% in comparison to native biomass. DGB and DGS15 individually yielded 0.64 g/g and 0.82 g/g lactic acid respectively, where as their co-cultivation led to effective utilisation of both glucose and xylose within 15 h (70%) and complete utilisation in 48 h, producing 49.75 g/L LA with a yield of 0.98 g/g and productivity of 1.036 g/L/h, and resulting in reduction in fermentation time. Separate hydrolysis of rice straw and co-fermentation (SHCF) of hydrolysates by Bacillus spp. enhanced the production of lactic acid, can circumvent challenges in biorefining of lignocellulosic biomass.

Sustainable biorefinery approach by utilizing xylose fraction of lignocellulosic biomass

Lignocellulosic biomass (LCB) has been a lucrative feedstock for developing biochemical products due to its rich organic content, low carbon footprint and abundant accessibility. The recalcitrant nature of this feedstock is a foremost bottleneck. It needs suitable pretreatment techniques to achieve a high yield of sugar fractions such as glucose and xylose with low inhibitory components. Cellulosic sugars are commonly used for the bio-manufacturing process, and the xylose sugar, which is predominant in the hemicellulosic fraction, is rejected as most cell factories lack the five‑carbon metabolic pathways. In the present review, more emphasis was placed on the efficient pretreatment techniques developed for disintegrating LCB and enhancing xylose sugars. Further, the transformation of the xylose to value-added products through chemo-catalytic routes was highlighted. In addition, the review also recapitulates the sustainable production of biochemicals by native xylose assimilating microbes and engineering the metabolic pathway to ameliorate biomanufacturing using xylose as the sole carbon source. Overall, this review will give an edge on the bioprocessing of microbial metabolism for the efficient utilization of xylose in the LCB.

Expansion Improved the Physical and Chemical Properties and In Vitro Rumen Digestibility of Buckwheat Straw

The hard texture and poor palatability of straw are important factors that hinder its application in feed. Expansion is a technology that can improve the utilization of biomass, but few studies have comprehensively revealed how to change physicochemical characteristics to improve nutritional value. In this study, mechanical and chemical methods were combined to study the texture properties, rheological properties, and physicochemical structures of straw, and its utilization value was evaluated by in vitro rumen digestion. Expansion caused hemicellulose degradation, cellulose separation, and lignin redistribution, resulting in a decrease in crystallinity. The hardness and chewiness of expanded straw were reduced by 55% to 66%, significantly improving palatability. The compressive stress could be reduced by 54-73%, and the relaxation elasticity was reduced by 5% when expanded straw was compressed. The compression deformation of expanded straw was doubled compared to feedstock, and the compacting degree was improved. Expanded straw significantly improved digestibility and gas production efficiency, which was due to the pore structure increasing the attachment of rumen microorganisms; besides that, the reduction of the internal structural force of the straw reduced energy consumption during digestion. The lignin content decreased by 10%, the hardness decreased further in secondary expansion, but the digestibility did not improve significantly.

The key role of pretreatment for the one-step and multi-step conversions of European lignocellulosic materials into furan compounds

Nowadays, an increased interest from the chemical industry towards the furanic compounds production, renewable molecules alternatives to fossil molecules, which can be transformed into a wide range of chemicals and biopolymers. These molecules are produced following hexose and pentose dehydration. In this context, lignocellulosic biomass, owing to its richness in carbohydrates, notably cellulose and hemicellulose, can be the starting material for monosaccharide supply to be converted into bio-based products. Nevertheless, processing biomass is essential to overcome the recalcitrance of biomass, cellulose crystallinity, and lignin crosslinked structure. The previous reports describe only the furanic compound production from monosaccharides, without considering the starting raw material from which they would be extracted, and without paying attention to raw material pretreatment for the furan production pathway, nor the mass balance of the whole process. Taking account of these shortcomings, this review focuses, firstly, on the conversion potential of different European abundant lignocellulosic matrices into 5-hydroxymethyl furfural and 2-furfural based on their chemical composition. The second line of discussion is focused on the many technological approaches reported so far for the conversion of feedstocks into furan intermediates for polymer technology but highlighting those adopting the minimum possible steps and with the lowest possible environmental impact. The focus of this review is to providing an updated discussion of the important issues relevant to bringing chemically furan derivatives into a market context within a green European context.

Efficient Secretory Production of Lytic Polysaccharide Monooxygenase BaLPMO10 and Its Application in Plant Biomass Conversion

Lytic polysaccharide monooxygenases (LPMOs) can oxidatively break the glycosidic bonds of crystalline cellulose, providing more actionable sites for cellulase to facilitate the conversion of cellulose to cello-oligosaccharides, cellobiose and glucose. In this work, a bioinformatics analysis of BaLPMO10 revealed that it is a hydrophobic, stable and secreted protein. By optimizing the fermentation conditions, the highest protein secretion level was found at a IPTG concentration of 0.5 mM and 20 h of fermentation at 37 °C, with a yield of 20 mg/L and purity > 95%. The effect of metal ions on the enzyme activity of BaLPMO10 was measured, and it was found that 10 mM Ca²⁺ and Na⁺ increased the enzyme activity by 47.8% and 98.0%, respectively. However, DTT, EDTA and five organic reagents inhibited the enzyme activity of BaLPMO10. Finally, BaLPMO10 was applied in biomass conversion. The degradation of corn stover pretreated with different steam explosions was performed. BaLPMO10 and cellulase had the best synergistic degradation effect on corn stover pretreated at 200 °C for 12 min, improving reducing sugars by 9.2% compared to cellulase alone. BaLPMO10 was found to be the most efficient for ethylenediamine-pretreated Caragana korshinskii by degrading three different biomasses, increasing the content of reducing sugars by 40.5% compared to cellulase alone following co-degradation with cellulase for 48 h. The results of scanning electron microscopy revealed that BaLPMO10 disrupted the structure of Caragana korshinskii, making its surface coarse and poriferous, which increased the accessibility of other enzymes and thus promoted the process of conversion. These findings provide guidance for improving the efficiency of enzymatic digestion of lignocellulosic biomass.

Advances in extraction and purification of citrus flavonoids

Flavonoids are the representative active substances of citrus with various biological activities and high nutritional value. In order to evaluate and utilize citrus flavonoids, isolation and purification are necessary steps. This manuscript reviewed the research advances in the extraction and purification of citrus flavonoids. The structure classification, the plant and nutritional functions, and the biosynthesis of citrus flavonoids were summarized. The characteristics of citrus flavonoids and the selection of separation strategies were explained. The technical system of extraction and purification of citrus flavonoids was systematically described. Finally, outlook and research directions were proposed.

Correlation of steam explosion severity with morphological and physicochemical characterization of soybean meal

Steam explosion, a novel effective technology for cereal modification, integrates high-temperature autohydrolysis and structural disruption, which can significantly influence the morphological and physicochemical characterization of the feedstocks. The deep knowledge of the structural changes that are brought about by the treatment severity is connected with the technological demands to improve the processing efficiency and to increase the industrial application of the feedstocks by steam explosion. In this study, the changes in morphological and physicochemical properties of soybean meal induced by steam explosion were investigated. The correlation of steam explosion severity with soybean meal's final quality was also analyzed. The results showed that steam explosion effectively increased the fractal dimension from 1.6553 to 1.8871, the glycinin content from 151.38 to 334.94 mg/g, and the 2,2-diphenylpicrylhydrazyl (DPPH) radical scavenging activity from 28.69 to 63.78%. The gray value, color (L* and a* values), and the total phenol and polysaccharide contents of soybean meal were reduced with greater steam explosion severity. Steam explosion severity had a remarkable positive correlation with the fractal dimension and DPPH radical scavenging activity. However, steam explosion severity had no significant correlation with the textural and adsorption properties of the soybean meal. This study focused on the morphological and physicochemical property changes of the soybean meal during a steam explosion process, which could guide the application of steam explosion in food systems.

Effect of steam explosion on nutritional components, physicochemical and rheological properties of brown rice powder

Brown rice powder is underutilized mainly due to its lower starch digestibility and poor processing performance. The present study investigated the potential of steam explosion on the improvement of nutritional and physicochemical characteristic in brown rice powder and rheological property of paste. Compared with native brown rice powder, steam explosion at 0.5 MPa for 7 min increased the water-extractable arabinoxylans (5.77%), reducing sugar content (21.04%), and iodine blue value (30.38%), which indicated steam explosion that destroyed the intact cells of brown rice. Later the crystalline structure of brown rice powder was destroyed into an amorphous structure by steam explosion. Steam explosion enhanced the degree of gelatinization (4.76~351.85%) and solvent retention capacity (SRC) of brown rice powder, compared with native sample. The effect on the intact cells and starch structure of brown rice caused the starch digestibility enhancement remarkable. Viscoelastic profiles confirmed that steam explosion weakened the paste strength and elasticity corresponded with hardness and cohesiveness by increasing the loss factor (tanδ). This work provided important information for brown rice powder modified by steam explosion (0.5 MPa, 7 min) with good nutritional property (nutrients and digestibility) and processability (SRC, textural, and rheological property). Steam exploded brown rice powder (0.5 MPa, 7 min) could serve as a potential ingredient widely used in food products.

Isolation and characterization of thermostable and alkali-tolerant cellulase from litter endophytic fungus Bartalinia pondoensis

Endophytic fungi in plant tissues produce a wide range of secondary metabolites and enzymes, which exhibit a variety of biological activities. In the present study, litter endophytic fungi were isolated from a fire-prone forest and screened for thermostable cellulases. Among nine endophytic fungi tested, two isolates, Bartalinia pondoensis and Phoma sp., showed the maximum cellulase activity. Bartalinia pondoensis was further selected for its cellulase production and characterization. Among the carbon and nitrogen sources tested, maximum cellulase production was observed with maltose and yeast extract, and the eucalyptus leaves and rice bran served as the best natural substrates. The cellulase activity increased with increasing temperature, with maximum activity recorded at 100 °C. The maximum CMCase activity was observed between pH 6.0 and 7.0 and retained 80% of its activity in the pH range of 8-10. Partially purified cellulase of B. pondoensis retained 50% of its activity after 2 h of incubation at 60 °C, 80 °C and 100 °C. These results suggest that litter endophytic fungus B. pondoensis is a potential source for the production of thermostable and alkali-tolerant cellulase.

Improving bioaccessibility and physicochemical property of blue-grained wholemeal flour by steam explosion

Whole grain contains many health-promoting ingredients, but due to its poor bioaccessibility and processibility, it is not widely accepted by consumers. The steam explosion was exploited to modify the nutritional bioaccessibility and the physicochemical properties of wholemeal flour in this study. In vitro starch digestibility, in vitro protein digestibility of wholemeal flour, total flavonoids content, and total phenolics content of digestive juice were used to evaluate the bioaccessibility, and a significant variation (p < 0.05) was noted. Results showed that steam explosion enhanced the gastric protein digestibility ranged from 5.67 to 6.92% and the intestinal protein digestibility ranged from 16.77 to 49.12%. Steam-exploded wholemeal flour (0.5 MPa, 5 min) had the highest protein digestibility and rapidly digestible starch content. Compared with native flour, steam explosion (0.5 MPa, 5 min) contributed to a 0.72-fold and 0.33-fold increment of total flavonoids content and total phenolics content in digestible juice. Chemical changes of wholemeal flour, induced by steam explosion, caused the changes in the solvent retention capacity, rheological property of wholemeal flour, and altered the falling number (and liquefaction number). An increasing tendency to solid-like behavior and the gel strength of wholemeal flour was significantly enhanced by the steam explosion at 0.5 MPa for 5 min, while the gluten was not weakened. This study indicated that steam-exploded wholemeal flour (0.5 MPa, 5 min) could serve as a potential ingredient with the noticeable bioaccessibility and physicochemical properties in cereal products.

Improving Antioxidative and Antiproliferative Properties Through the Release of Bioactive Compounds From Eucommia ulmoides Oliver Bark by Steam Explosion

Eucommia ulmoides Oliver bark is a potential medicinal plant-based feedstock for bioactive products and possesses the effective functions of antioxidant and antitumor. Network pharmacology was employed to reveal the oxidative and free radical damage and cancer-related potential compounds of Eucommia ulmoides Oliver in this study. The result showed that quercetin might be the key compound to resist these two types of diseases. Then, the effect of steam explosion on the release of bioactive compounds and the antioxidative and antiproliferative properties of the extract from Eucommia ulmoides Oliver bark were investigated. Results showed that steam explosion at 0.7 MPa for 30 min significantly enhanced the total phenolic, total flavonoids, and quercetin content of Eucommia ulmoides Oliver bark. Reducing power and 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radical scavenging activity of the steam-exploded extracting solution were 1.72 and 2.76 times of native. The antiproliferative activity to CT26 and HepG2 of the extract from steam-exploded Eucommia ulmoides Oliver bark (SEU) was higher than those of native-exploded Eucommia ulmoides Oliver bark (NEU). All these results suggested that steam explosion could be applied to release the bioactive compounds, thus enhanced the antioxidative and antiproliferative activities of medicinal and edible plant-based sources.

Effect of Steam Explosion on Structural Characteristics of β-Conglycinin and Morphology, Chemical Compositions of Soybean Meal

In this study, steam explosion was applied as a means to degrade β-conglycinin. We investigated changes in morphology, the chemical composition of soybean meal, and the structural characteristics of β-conglycinin. The results showed that steam explosion at 0.7 MPa for 8 min could effectively decrease the β-conglycinin content of soybean meal while the histamine content was not increased. The structural characteristics of soybean meal proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD), and X-ray diffraction (XRD). Steam explosion caused the degradation of high weight proteins and reduced the band density of α', α, and β subunits in β-conglycinin. The micro-surface of soybean meal seemed to be in the cracked or puffed stage and the color became brown or dark after steam explosion. Steam explosion facilitated the dissolution of water-extractable arabinoxylans, which are 4.81 fold higher than that of native soybean meal. Phytic acid was exposed to the hydrothermal environment of the steam explosion process and consequently degraded by 12.95-24.69%. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity of soybean meal extract was gradually increased from 20.70 to 33.71% with the rising of treated pressure from 0.3 to 0.7 MPa, which was 1.11-1.81 fold of native extract. The steam explosion may be a new modification technology that could decrease antigenicity, and steam-exploded soybean meal (0.7 MPa, 8 min) with lower β-conglycinin and phytic acid content that could be widely used in food products.

Thermo-Mechanical and Fungi Treatment as an Alternative Lignin Degradation Method for Bambusa oldhamii and Guadua angustifolia Fibers

Different strategies have been used to degrade the molecular structure of lignins in natural fibers. Both chemical and biological processes can obtain different types of lignins for industrial use. In this study, a variation of the spectral intensity of the thermo-mechanical and fungi-modified Bambusa oldhamii (giant bamboo) and Guadua angustifolia Kunt fibers were examined via Fouriertransform infrared spectroscopy. The giant bamboo and Guadua angustifolia Kunt specimens were modified using a non-chemical alternative steam pressure method for degrading lignins, followed by mechanical sieving to obtain fibers of different lengths. The obtained fibers were treated with the Fusarium incarnatum-equiseti MF18MH45591 strain in a 21 d degradation process. The samples were subjected to Fouriertransform infrared spectroscopy before and after the strain treatment. The intensity variation was found to be in the spectral range of 1200 cm⁻¹ to 1800 cm⁻¹, in which lignin components are commonly found in most plant species. A multivariate analysis of the principal components of the treated and untreated control samples confirmed the changes in the spectral region of interest, which were associated with the thermo-mechanical and fungal treatment.

Liquid hot water as sustainable biomass pretreatment technique for bioenergy production: A review

In recent years, lignocellulosic biomass has emerged as one of the most versatile energy sources among the research community for the production of biofuels and value-added chemicals. However, biomass pretreatment plays an important role in reducing the recalcitrant properties of lignocellulose, leading to superior quality of target products in bioenergy production. Among existing pretreatment techniques, liquid hot water (LHW) pretreatment has several outstanding advantages compared to others including minimum formation of monomeric sugars, significant removal of hemicellulose, and positive environmental impacts; however, several constraints of LHW pretreatment should be clarified. This contribution aims to provide a comprehensive analysis of reaction mechanism, reactor characteristics, influencing factors, techno-economic aspects, challenges, and prospects for LHW-based biomass pretreatment. Generally, LHW pretreatment could be widely employed in bioenergy processing from biomass, but circular economy-based advanced pretreatment techniques should be further studied in the future to achieve maximum efficiency, and minimum cost and drawbacks.

Loop engineering of a thermostable GH10 xylanase to improve low-temperature catalytic performance for better synergistic biomass-degrading abilities

Lignocellulosic biorefining for producing biofuels poses technical challenges. It is usually conducted over a long time using heat, making it energy intensive. In this study, we lowered the energy consumption of this process through an optimized enzyme and pretreatment strategy. First, the dominant mutant M137E/N269G of Bispora sp. MEY-1XYL10C_ΔN was obtained by directed evolution with highcatalytic efficiency (970 mL/s∙mg)and specific activity (2090 U/mg)at 37 °C, and thermostability was improved (T₅₀ increased by5 °C). After pretreatment with seawater immersionfollowing steam explosion,bagasse was co-treated with cellulase and M137E/N269G under mild conditions (37 °C), the resulting highest yield of fermentable sugars reached 219 µmol/g of bagasse,46% higher than that of the non-seawater treatment group, with the highest degree of synergy of 2.0. Pretreatment with seawater following steam explosion and synergistic hydrolysis through high activity xylanase and cellulase helped to achieve low energy degradation of lignocellulosic biomass.

Steam Explosion Pretreatment of Lignocellulosic Biomass: A Mini-Review of Theorical and Experimental Approaches

Steam Explosion (SE) is one of the most efficient and environmentally friendly processes for the pretreatment of lignocellulosic biomass. It is an important tool for the development of the biorefinery concept to mitigate the recalcitrance of biomass. However, the two distinct steps of SE, steam cracking and explosive decompression, leading to the breakdown of the lignocellulosic matrix have generally been studied in empiric ways and clarification are needed. This mini-review provides new insights and recommendations regarding the properties of subcritical water, process modeling and the importance of the depressurization rate.

Recent advances in green solvents for lignocellulosic biomass pretreatment: Potential of choline chloride (ChCl) based solvents

Biomass wastes exhibit a great potential to be used as a source of non-depleting renewable energy and synthesis of value-added products. The key to the valorization of excess lignocellulosic biomass wastes in the world lies on the pretreatment process to recalcitrant barrier of the lignocellulosic material for the access to useful substrates. A wide range of pretreatment techniques are available and advances in this field is continuously happening, in search for cheap, effective, and environmentally friendly methods. This review starts with an introduction to conventional approaches and green solvents for pretreatment of lignocellulosic biomass. Subsequently, the mechanism of actions along with the advantages and disadvantages of pretreatment techniques were reviewed. The roles of choline chloride (ChCl) in green solvents and their potential applications were also comprehensively reviewed. The collection of ideas in this review serve as an insight for future works or interest on biomass-to-energy conversion using green solvents.

Advances in Pretreatment of Straw Biomass for Sugar Production

Straw biomass is an inexpensive, sustainable, and abundant renewable feedstock for the production of valuable chemicals and biofuels, which can surmount the main drawbacks such as greenhouse gas emission and environmental pollution, aroused from the consumption of fossil fuels. It is rich in organic content but is not sufficient for extensive applications because of its natural recalcitrance. Therefore, suitable pretreatment is a prerequisite for the efficient production of fermentable sugars by enzymatic hydrolysis. Here, we provide an overview of various pretreatment methods to effectively separate the major components such as hemicellulose, cellulose, and lignin and enhance the accessibility and susceptibility of every single component. This review outlines the diverse approaches (e.g., chemical, physical, biological, and combined treatments) for the excellent conversion of straw biomass to fermentable sugars, summarizes the benefits and drawbacks of each pretreatment method, and proposes some investigation prospects for the future pretreatments.

Persea Americana Agro-Industrial Waste Biorefinery for Sustainable High-Value-Added Products

Significant problems have arisen in recent years, such as global warming and hunger. These complications are related to the depletion and exploitation of natural resources, as well as environmental pollution. In this context, bioprocesses and biorefinery can be used to manage agro-industrial wastes for obtaining high-value-added products. A large number of by-products are composed of lignin and cellulose, having the potential to be exploited sustainably for chemical and biological conversion. The biorefinery of agro-industrial wastes has applications in many fields, such as pharmaceuticals, medicine, material engineering, and environmental remediation. A comprehensive approach has been developed toward the agro-industrial management of avocado (Persea americana) biomass waste, which can be transformed into high-value-added products to mitigate global warming, save non-renewable energy, and contribute to health and science. Therefore, this work presents a comprehensive review on avocado fruit waste biorefinery and its possible applications as biofuel, as drugs, as bioplastics, in the environmental field, and in emerging nanotechnological opportunities for economic and scientific growth.

Production of oligosaccharides and biofuels from Miscanthus using combinatorial steam explosion and ionic liquid pretreatment

Pretreatment strategies are fundamental to effectively deconstruct lignocellulosic biomass and economically produce biofuels, biomaterials and bio-based chemicals. This study evaluated individual and combinatorial steam explosion (SE) and ionic liquid (IL) pretreatments for production of high-value oligosaccharides from a novel seed-based Miscanthus hybrid (Mx2779). The two ILs used for pretreatment were triethylammonium hydrogen sulphate [TEA][HSO₄] and 1-ethyl-3-methylimidazolium acetate [C₂mim][OAc]. The results showed that each pretreatment leads to distinct effects on the fragmentation (cellulose and xylan dissolution, delignification, deacetylation) and physicochemical modification (cellulose and lignin properties) of lignocellulose. This, in turn, dictated enzymatic hydrolysis efficiencies of the cellulose pulp to glucose or gluco-oligosaccharides for downstream applications. Our findings suggest that the stand-alone SE or [C₂mim][OAc] pretreatments may offer cost advantages over [TEA][HSO₄] through the production of oligosaccharides such as xylo- and gluco-oligosaccharides. This study also highlights technical and economic pretreatment process challenges related to the production of oligosaccharides from Miscanthus Mx2779 biomass.

One-pot production of lactic acid from rice straw pretreated with ionic liquid

Production of platform chemicals has been advocated as a sustainable option to tackle the problems associated with agro-waste management. In this report, for the first time, efforts were made to effectively produce second-generation lactic acid from rice straw pretreated with imidazolium ionic liquid [EMIM][OAc] and subsequently fermented with a promising Lactobacillus plantarum SKL-22 strain saccharified with a commercial cellulase enzyme. Medium optimization was carried out to enhance the lactic acid (LA) yield by response surface methodology. In a 5 L bioreactor, the process was further upscale, and a yield increment of 1.11% was observed. The process using rice straw as substrate led to a LA yield of 36.75 g/L from L. plantarum SKL-22 in a single pot bioprocess. Overall, the above finding has shown the ability of L. plantarum SKL-22 to produce LA from the hydrolysate of rice straw. This study presented a novel environmental-friendly method for LA production.

Plant Biosystems Design Research Roadmap 1.0

Human life intimately depends on plants for food, biomaterials, health, energy, and a sustainable environment. Various plants have been genetically improved mostly through breeding, along with limited modification via genetic engineering, yet they are still not able to meet the ever-increasing needs, in terms of both quantity and quality, resulting from the rapid increase in world population and expected standards of living. A step change that may address these challenges would be to expand the potential of plants using biosystems design approaches. This represents a shift in plant science research from relatively simple trial-and-error approaches to innovative strategies based on predictive models of biological systems. Plant biosystems design seeks to accelerate plant genetic improvement using genome editing and genetic circuit engineering or create novel plant systems through de novo synthesis of plant genomes. From this perspective, we present a comprehensive roadmap of plant biosystems design covering theories, principles, and technical methods, along with potential applications in basic and applied plant biology research. We highlight current challenges, future opportunities, and research priorities, along with a framework for international collaboration, towards rapid advancement of this emerging interdisciplinary area of research. Finally, we discuss the importance of social responsibility in utilizing plant biosystems design and suggest strategies for improving public perception, trust, and acceptance.

Sugars Production from Municipal Forestry and Greening Wastes Pretreated by an Integrated Steam Explosion-Based Process

Increasing awareness of resource sustainability and waste management has led to the search for solutions while promoting circular economy principles. Among all kinds of lignocellulosic biomass available, one with growing interest is municipal forestry and greening waste (MFGW). MFGW makes up an important part of waste streams of municipal solid waste and is a potential feedstock for biological conversion in a lignocellulosic biorefinery. This work studied the fermentable sugars production from MFGW after steam explosion (SE) pretreatment combined with other pretreatments such as dilute acid, organosolv, and metal salts. A range of pretreatment conditions was evaluated according to different parameters: sugars recovery, degradation product generation, and enzymatic hydrolysis yield. At selected pretreatment conditions (diluted acid plus SE, 195 °C, 10 min, and 60 mg H2SO4/g MFGW), 77% of potential sugars content in MFGW was obtained. The effect of solids loading and enzyme dose on glucose release and glucose yield on enzymatic hydrolysis were also determined. Up to 70% of the main sugars in the MFGW were recovered for the coupled pretreatment and enzymatic hydrolysis (45 FPU/g glucan enzyme loading and 20% dry matter solid consistency), resulting in 80 g/L glucose that could be further utilized for ethanol production.

Effects of steam explosion pretreatment on the composition and biological activities of tartary buckwheat bran phenolics

Steam explosion (SE) is an efficient technology to disrupt materials for improving their quality. In this study, SE was applied to release phenolics and improve the roughening of tartary buckwheat bran. The results showed that SE promoted the dissolution of phenolics, particularly, the content of the bound fraction was nearly increased by two times (0.36 vs. 0.99 mg GAE per g DW). The analysis of the phenolic composition showed that SE improved the liberation of bound pyrogallic acid, protocatechuic acid and caffeic acid. The biological activity tests indicated that SE effectively enhanced the oxygen radical absorbance capacity (ORAC) in vitro of the extract of bound phenolics by 270%. It also improved the cellular antioxidant activity (CAA) in vitro of the extract of free phenolics by 215%. Furthermore, SE showed potential in improving the antiproliferative activity of the total phenolic extract against Caco-2 cells as well as the bound phenolic extract against HepG2 cells in vitro.

Pilot-scale production of xylo-oligosaccharides and fermentable sugars from Miscanthus using steam explosion pretreatment

This study investigated pilot-scale production of xylo-oligosaccharides (XOS) and fermentable sugars from Miscanthus using steam explosion (SE) pretreatment. SE conditions (200 °C; 15 bar; 10 min) led to XOS yields up to 52 % (w/w of initial xylan) in the hydrolysate. Liquid chromatography-mass spectrometry demonstrated that the solubilised XOS contained bound acetyl- and hydroxycinnamate residues, physicochemical properties known for high prebiotic effects and anti-oxidant activity in nutraceutical foods. Enzymatic hydrolysis of XOS-rich hydrolysate with commercial endo-xylanases resulted in xylobiose yields of 380 to 500 g/kg of initial xylan in the biomass after only 4 h, equivalent to ~74 to 90 % conversion of XOS into xylobiose. Fermentable glucose yields from enzymatic hydrolysis of solid residues were 8 to 9-fold higher than for untreated material. In view of an integrated biorefinery, we demonstrate the potential for efficient utilisation of Miscanthus for the production of renewable sources, including biochemicals and biofuels.

Redesigning the Aspergillus nidulans xylanase regulatory pathway to enhance cellulase production with xylose as the carbon and inducer source

Background

Biomass contains cellulose (C6-sugars), hemicellulose (C5-sugars) and lignin. Biomass ranks amongst the most abundant hydrocarbon resources on earth. However, biomass is recalcitrant to enzymatic digestion by cellulases. Physicochemical pretreatment methods make cellulose accessible but partially destroy hemicellulose, producing a C5-sugar-rich liquor. Typically, digestion of pretreated LCB is performed with commercial cellulase preparations, but C5-sugars could in principle be used for “on site” production of cellulases by genetically engineered microorganism, thereby reducing costs.

Results

Here we report a succession of genetic interventions in Aspergillus nidulans that redesign the natural regulatory circuitry of cellulase genes in such a way that recombinant strains use C5-sugar liquors (xylose) to grow a vegetative tissue and simultaneously accumulate large amounts of cellulases. Overexpression of XlnR showed that under xylose-induction conditions only xylanase C was produced. XlnR overexpression strains were constructed that use the xynCp promoter to drive the production of cellobiohydrolases, endoglucanases and β-glucosidase. All five cellulases accumulated at high levels when grown on xylose. Production of cellulases in the presence of pretreated-biomass C5-sugar liquors was investigated, and cellulases accumulated to much higher enzyme titers than those obtained for traditional fungal cell factories with cellulase-inducing substrates.

Conclusions

By replacing expensive substrates with a cheap by-product carbon source, the use of C5-sugar liquors directly derived from LCB pretreatment processes not only reduces enzyme production costs, but also lowers operational costs by eliminating the need for off-site enzyme production, purification, concentration, transport and dilution.

Immobilization of cellulase in the non-natural ionic liquid environments to enhance cellulase activity and functional stability

Ionic liquids (ILs) have been applied as an environmentally friendly solvent in the pretreatment of lignocellulosic biomass for more than a decade. The ILs involved pretreatment processes for cellulases mediated saccharification lead to both the breakdown of cellulose crystallinity and the decrease of lignin content, thereby improving the solubility of cellulose and the accessibility of cellulase. However, most cellulases are partially or completely inactivated in the presence of even low amount of ILs. Immobilized cellulases are found to perform improved stability and higher apparent activity in practical application compared with its free counterparts. Enzyme immobilization therefore has become a promising way to relieve the deactivation of cellulase in ILs. Various immobilization carriers and methods have been developed and achieved satisfactory results in improving the stability, activity, and recycling of cellulases in IL pretreatment systems. This review aims to provide detailed introduction of immobilization methods and carrier materials of cellulase, including natural polysaccharides, synthetic polymers, inorganic materials, magnetic materials, and newly developed composite materials, and illustrate key methodologies in improving the performance of cellulase in the presence of ILs. Especially, novel materials and concepts from the recently representative researches are focused and discussed comprehensively, and future trends in immobilization of cellulases in non-natural ILs environments are speculated in the end.

Biodegradation of lignin by Pseudomonas sp. Q18 and the characterization of a novel bacterial DyP-type peroxidase

Lignin valorization can be obtained through cleavage of selected bonds by microbial enzymes, in which lignin is segregated from cellulose and hemicellulose and abundant phenolic compounds can be provided. In this study, Pseudomonas sp. Q18, previously isolated from rotten wood in China, was used to degrade alkali lignin and raw lignocellulosic material. Gel-permeation chromatography, field-emission scanning electron microscope, and GC-MS were combined to investigate the degradation process. The GC-MS results revealed that the quantities of aromatic compounds with phenol ring from lignin increased significantly after incubation with Pseudomonas sp. Q18, which indicated the degradation of lignin. According to the lignin-derived metabolite analysis, it was proposed that a DyP-type peroxidase (PmDyP) might exist in strain Q18. Thereafter, the gene of PmDyP was cloned and expressed, after which the recombinant PmDyP was purified and the enzymatic kinetics of PmDyP were assayed. According to results, PmDyP showed promising characteristics for lignocellulosic biodegradation in biorefinery.

Eco-friendly process combining acid-catalyst and thermomechanical pretreatment for improving enzymatic hydrolysis of hemp hurds

The aim of this study was to investigate a pretreatment by combined H₂SO₄ acid-catalyst and thermomechanical process to improve hemicelluloses solubilization of hemp hurds and subsequently enzymatic hydrolysis extent of potentially fermentable sugars. It was found that the sugars released were gradually increased with treatment severity. Soluble sugars generated before enzymatic hydrolysis (R₁) increased up to 2.23 g/L indicating that autohydrolysis reaction occurred during pretreatment. Consequently, the solubilization of hemicelluloses was correlated with combined severity factor (CS). As a result, increase of overall reducing sugars (ORS) from 23.4% (untreated) to 81.4% was observed at optimized conditions of steaming temperature of 165 °C for 30 min and acid loading of 62.9 g/kg DM (dry material) corresponding to CS = 1.2, with limited production of identified by-products: 0.035 g/L and 0.46 g/L (per 100 g DM) for furfural and HMF, respectively. Structural and physicochemical modifications of biomass were observed by FTIR, A_BET and SEM.

High-level expression of an engineered β-mannanase (mRmMan5A) in Pichia pastoris for manno-oligosaccharide production using steam explosion pretreated palm kernel cake

An engineered β-mannanase (mRmMan5A) from Rhizomucor miehei was successfully expressed in Pichia pastoris. Through high cell density fermentation, the expression level of mRmMan5A reached 79,680 U mL^-1. The mRmMan5A showed maximum activity at pH 4.5 and 65 °C, and exhibited high specific activities towards mannans. To produce manno-oligosaccharides, palm kernel cake (PKC) was pretreated by steam explosion at 200 °C for 7.5 min, and then hydrolyzed by mRmMan5A. As a result, the total manno-oligosaccharide yield reached 34.8 g/100 g dry PKC, indicating that 80.6% of total mannan in PKC was hydrolyzed. Moreover, the kilo-scale production of manno-oligosaccharides was carried out to verify the feasibility of mass production. A total of 261.3 g manno-oligosaccharides were produced from 1.0 kg of dry PKC. An effective β-mannanase for the bioconversion of mannan-rich biomasses and an efficient method for the production of manno-oligosaccharides from PKC are provided in this paper.

Economic, Environmental and Moral Acceptance of Renewable Energy: A Case Study-The Agricultural Biogas Plant at Pěčín

The production of renewable energy in agricultural biogas plants is being widely criticized because-among other things-most of the feedstock comes from purpose-grown crops like maize. These activities (generously subsidized in the Czech Republic) generate competitive pressure to other crops that are used for feeding or food production, worsening their affordability. Unique pretreatment technology that allows substitution of the purpose-grown crops by farming residues (such as husk or straw) was built 6 years ago on a commercial basis in Pěčín (Czech Republic) under modest funding and without publicity. The design of the concept; financial assessment and moral viewpoint were analyzed based on practical operating data. It showed that the apparatus improves economic, environmental and moral acceptance as well. However, according to the government's view, public funding for this type of processing was shortened, "because waste materials represent a lower cost". The impact of such governance was analyzed as well.

Combinatorial pretreatment and fermentation optimization enabled a record yield on lignin bioconversion

BACKGROUND

Lignin valorization has recently been considered to be an essential process for sustainable and cost-effective biorefineries. Lignin represents a potential new feedstock for value-added products. Oleaginous bacteria such as Rhodococcus opacus can produce intracellular lipids from biodegradation of aromatic substrates. These lipids can be used for biofuel production, which can potentially replace petroleum-derived chemicals. However, the low reactivity of lignin produced from pretreatment and the underdeveloped fermentation technology hindered lignin bioconversion to lipids. In this study, combinatorial pretreatment with an optimized fermentation strategy was evaluated to improve lignin valorization into lipids using R. opacus PD630.

RESULTS

As opposed to single pretreatment, combinatorial pretreatment produced a 12.8-75.6% higher lipid concentration in fermentation using lignin as the carbon source. Gas chromatography-mass spectrometry analysis showed that combinatorial pretreatment released more aromatic monomers, which could be more readily utilized by lignin-degrading strains. Three detoxification strategies were used to remove potential inhibitors produced from pretreatment. After heating detoxification of the lignin stream, the lipid concentration further increased by 2.9-9.7%. Different fermentation strategies were evaluated in scale-up lipid fermentation using a 2.0-l fermenter. With laccase treatment of the lignin stream produced from combinatorial pretreatment, the highest cell dry weight and lipid concentration were 10.1 and 1.83 g/l, respectively, in fed-batch fermentation, with a total soluble substrate concentration of 40 g/l. The improvement of the lipid fermentation performance may have resulted from lignin depolymerization by the combinatorial pretreatment and laccase treatment, reduced inhibition effects by fed-batch fermentation, adequate oxygen supply, and an accurate pH control in the fermenter.

CONCLUSIONS

Overall, these results demonstrate that combinatorial pretreatment, together with fermentation optimization, favorably improves lipid production using lignin as the carbon source. Combinatorial pretreatment integrated with fed-batch fermentation was an effective strategy to improve the bioconversion of lignin into lipids, thus facilitating lignin valorization in biorefineries.

Cellulose Biorefinery Based on a Combined Catalytic and Biotechnological Approach for Production of 5-HMF and Ethanol

In this study, a combination of catalytic and biotechnological processes was proposed for the first time for application in a cellulose biorefinery for the production of 5-hydroxymethylfurfural (5-HMF) and bioethanol. Hydrolytic dehydration of the mechanically activated microcrystalline cellulose over a carbon-based mesoporous Sibunt-4 catalyst resulted in moderate yields of glucose and 5-HMF (21.1-25.1 and 6.6-9.4 %). 5-HMF was extracted from the resulting mixture with isobutanol and subjected to ethanol fermentation. A number of yeast strains were isolated that also revealed high thermotolerance (up to 50 °C) and resistance to inhibitors found in the hydrolysates. The strains Kluyveromyces marxianus C1 and Ogataea polymorpha CBS4732 were capable of producing ethanol from processed catalytic hydrolysates of cellulose at 42 °C, with yields of 72.0±5.7 and 75.2±4.3 % from the maximum theoretical yield of ethanol, respectively.

Two-step size reduction and post-washing of steam exploded corn stover improving simultaneous saccharification and fermentation for ethanol production

The simultaneous saccharification and fermentation (SSF) of corn stover biomass for ethanol production was performed by integrating steam explosion (SE) pretreatment, hydrolysis and fermentation. Higher SE pretreatment severity and two-step size reduction increased the specific surface area, swollen volume and water holding capacity of steam exploded corn stover (SECS) and hence facilitated the efficiency of hydrolysis and fermentation. The ethanol production and yield in SSF increased with the decrease of particle size and post-washing of SECS prior to fermentation to remove the inhibitors. Under the SE conditions of 1.5MPa and 9min using 2.0cm particle size, glucan recovery and conversion to glucose by enzymes were 86.2% and 87.2%, respectively. The ethanol concentration and yield were 45.0g/L and 85.6%, respectively. With this two-step size reduction and post-washing strategy, the water utilization efficiency, sugar recovery and conversion, and ethanol concentration and yield by the SSF process were improved.

Enzymatic hydrolysis of lignocellulosic biomass from low to high solids loading

Solid state enzymatic hydrolysis (SSEH) has many advantages, such as higher sugar concentration, lower operating costs, and less energy input. It should be a potential approach for the industrial application of lignocellulosic ethanol. The purpose of this work is to review the enzymatic hydrolysis of lignocellulosic biomass from low to high solids loading and introduce its both challenges and perspectives. The limitations of SSEH, including inhibition effects, water constraint, and rheology characteristic, are summarized firstly. Various strategies for overcoming these limitations are proposed correspondingly. Fed batch process and its feeding strategy to improve the SSEH efficiency are then discussed. Finally, several intensification methods, hydrolysis reactor, and pilot- and demonstration-scale operations of SSEH are described. In-depth analysis of main limitations and development of novel intensification methods and reactors should provide an effective way to achieve large-scale implementation of SSEH.

Mechanical property of different corn stover morphological fractions and its correlations with high solids enzymatic hydrolysis by periodic peristalsis

Selective structure fractionation combined with periodic peristalsis was exploited to improve the conversion performance of corn stover. The increase of glucan and lignin content and the decrease of xylan content in stem pith were highest after SE, whereas they were lowest in stem node. Glucan conversion increased in this order: steam node<stem rind<whole corn stover (WCS)<stem pith<leaf sheath<leaf. Glucan conversion using periodic peristalsis increased by 10-17% before 24h compared with that using incubator shaker. Stem pith, leaf sheath, leaf, and WCS showed lower hardness and total work in texture profile analysis, resulting in higher glucan conversion compared with stem node and stem rind. Periodic peristalsis reduced hardness and total work before 24h, which was consistent with increased glucan conversion. Periodic peristalsis was an effective strategy to increase high solids enzymatic hydrolysis efficiency of different corn stover morphological fractions.