Corncob Residue Research Articles

Basic research about corncob residue as Lyocell spinning material

Using the corncob residue as a new cheaper source material for Lyocell spinning technology. Chemical properties of the corncob residue after extraction of hemicellulose and lignin were investigated in this paper. It was found that the main composition of corncob residue is cellulose, accompanied by slight hemicellulose and very tiny amount of spinning insoluble components. Compared to wood pulp, corncob residue has a similar number-average molecular weight, a slightly larger weight-average molecular weight, a lower peak-relative molecular weight, and a larger polydispersity. All those properties suggest that this kind of corncob residue has big potential to be used as spinning material for regenerated cellulose fiber. A new type corncob residue made fiber was produced, using the Lyocell spinning technology. Mechanical properties of the corncob residue fiber were analyzed. The corncob residue fiber has a tensile strength value between that of viscose fiber and Lyocell fiber, indicating its good application prospects. However, the corncob residue fiber has a high crystallinity and the orientation value with large fiber linear density, suggesting that the spinning technology needs to be further improved.

L-Lactic acid production by Bacillus coagulans through simultaneous saccharification and fermentation of lignocellulosic corncob residue

l-Lactic acid is an important monomer of polylactic acid, a biodegradable plastic. In this study, we systematically investigated l-lactic acid fermentation by thermophilic Bacillus coagulans strains using the corncob residue (CCR), a widely available lignocellulosic material. Our results showed that 68.0 g/L l-lactic acid was obtained with a high yield of 0.85 g/g cellulose by B. coagulans strain H-1 after 36 h in batch fermentation. Strain H-1 could produce 79.1 g/L l-lactic acid with a yield of 0.76 g/g cellulose after 84 h in fed-batch fermentation. The results suggest that attractive lignocellulosic wastes such as CCR could be used in the efficient biomanufacture of l-lactic acid.

Synergistic Effect of Different Species in Stannic Chloride Solution on the Production of Levulinic Acid from Biomass

Metal chloride has shown high potential in biomass conversion to valuable chemicals, but the nature of active species and the corresponding performances on each successive reaction step need further elucidation. In this work, SnCl4 was found to exhibit satisfactory catalytic activity, achieving 64.6 mol % yield of levulinic acid from corncob residue. The levulinic acid obtained could be further converted to more valuable ethyl levulinate with 85% yield without any extra catalyst addition. In water medium, the hydrolysis of SnCl4 resulted in the formation of stannic oxide, H+ and Cl–, which showed a synergistic effect and all contributed to levulinic acid production. It was demystified that Cl– promoted cellulose hydrolysis, and the formed H+ as Bronsted acid mainly contributed to cellulose hydrolysis and fructose dehydration, as well as HMF decomposition to levulinic acid. Sn(IV) species facilitated both glucose-to-fructose isomerization and fructose consumption yielding undesirable polymers, but exhibite...

Catalytic depolymerization of organosolv lignin to phenolic monomers and low molecular weight oligomers

The lignin-first strategy provides significant potential for producing value-added phenolics and high-quality biofuels. In this contribution, stepwise extraction and depolymerization of lignin in corncob residue towards the production of phenolic monomers, lignin-derived dimers and trimers was investigated. H2O/n-butanol (4:6, v/v) co-solvent could extract 87.1% of lignin in corncob residue, retaining a high-purity (86.0%) cellulose pulp. Ni/HZSM-5 catalysts with different Ni loadings were prepared and applied for further degradation of organosolv lignin. Over 5% Ni/HZSM-5, the highest yield of phenolic monomer was 19.5% with the selectivity of 66.7% towards 4-ethyl phenols (4-ethyl phenol and 4-ethyl guaiacol) at 300 °C, and liquid products with higher heating value (HHV) of 29.2 MJ kg−1 were obtained. The 5% Ni/HZSM-5 catalyst promoted the cleavage of intramolecular β-O-4 and Cβ-Cγ linkages, resulting in substantially decreased weight-average molecular weight (Mw)/number-average molecular weight (Mn) of the organosolv lignin from 2541/1064 Da to 562/391 Da, which implied the degradation of high-Mw oligomers to dimers and trimers. The catalyst also contributed to the hydrogenation of CαCβ bonds in unsaturated intermediates (coniferyl alcohol and coumaryl alcohol). The possible cleavage mechanism for the degradation of lignin-derived oligomers was also proposed.

Expansin assisted bio-affinity immobilization of endoxylanase from Bacillus subtilis onto corncob residue: Characterization and efficient production of xylooligosaccharides

A one-step method to immobilize xylanase onto cellulosic material by fusion of expansin from Bacillus subtilis to xylanase LC9 without the requirement of prior purification of enzyme has been developed. Fusion enzyme EXLX-R2-XYN was specifically adsorbed onto corncob residue with high loading capacity due to bio-affinity adsorption of expansin onto cellulose. The immobilization yield was close to 100%, with a recovered activity of 82.4%. The immobilized EXLX-R2-XYN retained 45.3% of its activity after incubation at 70 °C for 3 h, whereas only 16.3% of the activity was left in free form under the same conditions. The conversion yield of XOS by using immobilized EXLX-R2-XYN reached up to 515 mg/g xylan from 2% corncob extracted xylan, which was higher than that of the free enzyme. The hydrolysis products were mainly xylobiose (57.5%) and xylotriose (38.4%), without undesirable xylose production. After five cycles of hydrolysis, more than 70% of conversion was obtained.

A clean and effective potassium hydroxide pretreatment of corncob residue for the enhancement of enzymatic hydrolysis at high solids loading.

Corncob residue (CCR) is an economic feedstock with enormous potential for the production of bioethanol. In this work, potassium hydroxide (KOH) pretreatment of CCR was investigated under relatively mild conditions, and the effectiveness of KOH pretreatment was evaluated by enzymatic saccharification at high solid loading. Results showed that after KOH pretreatment (16 wt% KOH dosage at 70 °C for 90 min) and the enzymatic hydrolysis at 20% solids loading and 20 FPU g−1-substrate of cellulase loading, the glucose yield could reach up to about 91%, which was over 90% higher compared to the raw CCR without KOH pretreatment. Correspondingly, about 89% of lignin and 79% of extractives were removed after KOH pretreatment. In addition, the spent liquor of KOH pretreatment containing sylvite could be used as lignin-based fertilizer based on the concept of biorefinery. In this case, the entire process for the production of fermentable sugars was clean and sustainable, which is very vital for the conversion of lignocelluloses to bioenergy or chemicals.

Efficient l-lactic acid production from corncob residue using metabolically engineered thermo-tolerant yeast

Lactic acid is an important industrial product and the production from inexpensive and renewable lignocellulose can reduce the cost and environmental pollution. In this study, a Kluyveromyces marxianus strain which produced lactic acid efficiently from corncob was constructed. Firstly, two of six different lactate dehydrogenases, which from Plasmodium falciparum and Bacillus subtilis, respectively, were proved to be effective for l-lactic acid production. Then, five single genetic modifications were conducted. The overexpression of Saccharomyces cerevisiae proton-coupled monocarboxylate transporter, K. marxianus 6-phosphofructokinase, or disruption of K. marxianus putative d-lactate dehydrogenase enhanced the l-lactic acid accumulation. Finally, the strain YKX071, obtained via combination of above effective genetic engineering, produced 103.00 g/L l-lactic acid at 42 °C with optical purity of 99.5% from corncob residue via simultaneous saccharification and co-fermentation. This study first developed an effective platform for high optical purity l-lactic acid production from lignocellulose using yeast with inexpensive nitrogen sources.

Structure characterization and pyrolysis behavior of organosolv lignin isolated from corncob residue

Structural features and pyrolysis behavior of organosolv lignin isolated from corncob residue by THF-H2O solvent were studied. The average molecular weight (Mw) of the organosolv lignin, mainly constituted of p-hydroxyphenyl (H), guaiacyl (G), syringyl (S) and various substructures with β-O-4, β-β bonds, was mainly distributed between 10,000 and 600 g/mol, occupying about 81%. TG/DTG curves of the organosolv lignin showed three maximum weight loss peaks at about 120, 150 and 350 °C, respectively. The pyrolysis of organosolv lignin was performed through two ways, that is, one-step at different temperature (RT-120 °C, RT-150 °C, RT-350 °C) and stepwise (120–150 °C, 150–350 °C) pyrolysis over different temperature range. The results indicated that oligomers with molecular weight between 200 and 500 Da were the main products in bio-oil at the low temperature step, while high temperature step produced certain amount of monomers of phenols, guaiacols and syringols. The variation of structure and molecular weight distribution of pyrolyzed residues was further investigated.

Tracing cellulase components in hydrolyzate during the enzymatic hydrolysis of corncob residue and its analysis

Cellulase components in hydrolyzate were accurately traced by SDS-PAGE gel electrophoresis during the enzymatic hydrolysis of corncob residual (CCR) and delignified CCR (CCR-DL). After a quick initial adsorption on substrates, cellulase in hydrolyzate remained stable for CCR, but showed an obvious increasing trend for CCR-DL. It indicated that lignin in CCR was the main factor for the loss of cellulase in hydrolyzate. During CCR's hydrolysis, β‑glucosidase, xylanase, endoglucanase III (EGIII) and EGV were rapidly adsorbed on lignin and weren't released in subsequent, however, cellobiohydrolase I (CBHI), CBHII, EGI and EGIV were mainly adsorbed on cellulose in the early stage. With the hydrolysis of substrate, cellulase on cellulose would be released into hydrolyzate, but cellulase in hydrolyzate gradually became hydrophobic and much easier to be adsorb on lignin by the increasing hydrophobic interaction. These two factors dominated the change of cellulase concentration in hydrolyzate in the later stage of CCR's hydrolysis.

Production of levulinic acid from corn cob residue in a fed-batch acid hydrolysis process

Abstract Levulinic acid (LA) is an important platform chemical, the production of which by using biomass resources such as corncob is of great significance to the sustainable development. Traditional hydrolysis processes yield low concentrations of levulinic acid with large amounts of acid being consumed. In this paper, a new fed-batch process for hydrolyzing corncob residues with sulfuric acid being utilized as the catalysis to produce levulinic acid at high concentrations is proposed. The mass concentration of the levulinic acid increased with growing the times of feeding and a 107.93 g/L of the levulinic acid can be reached at the 7th hydrolysis. However, the yield of levulinic acid reduces gradually during the fed-batch process. To explore the phenomenon, the reaction mechanism of cellulose acid hydrolysis was experimentally studied. It can be deduced that the reduction of the levulinic acid yield was caused by the polymerization of the soluble humin analogues and the 5-hydroxymethyl furfural (5-HMF) as well as the glucose.

Corncob residual reinforced polyethylene composites considering the biorefinery process and the enhancement of performance

Abstract Aiming to improve the economic feasibility of the corncob biorefinery process, fibers, including the corncob bagasse, xylose-extracted corncob residue and the ethanol-processing residue, were used as the reinforcing phase for the preparation of wood plastic composites (WPCs). The mechanical properties and the weathering performance of the composites were compared. The results indicated that the WPCs reinforced by the ethanol-processing residue showed balanced advantages in mechanical properties and weathering performance. The effects of the compatibilizer and the cellulose/lignin mixture on the WPC properties were further evaluated, indicating that use of 4 wt % of Polyethylene-graft-maleic anhydride (PE-g-MA) as the compatibilizer and a mixture of the EPR with lignin at a ratio of (9:1) were the optimized conditions for WPCs. The current work showed potential in making full use of the solid residue of biorefinery processes and making the waste profitable.

The cellulose binding region in Trichoderma reesei cellobiohydrolase I has a higher capacity in improving crystalline cellulose degradation than that of Penicillium oxalicum

Commercial cellulase preparations for lignocellulose bioconversion are mainly produced by the fungus Trichoderma reesei. The maximum cellulose conversion of T. reesei cellulase mixture was 15%–20% higher than that of Penicillium oxalicum in the hydrolysis of corncob residue and Avicel. Nevertheless, both preparations hydrolyzed more than 92% of cellulose in NaOH-mercerized Avicel. When added to Avicel hydrolysis residue that was less reactive to P. oxalicum cellulases, cellobiohydrolase I (CBH I) from T. reesei resulted in a higher cellulose conversion than its homologous proteins from P. oxalicum and Aspergillus niger at the same protein loadings. Further domain exchange experiment attributed the high hydrolytic efficiency of T. reesei CBH I to its inter-domain linker and cellulose-binding domain. The results in part explained the superior performance of T. reesei cellulases on the degradation of native crystalline cellulose, and highlighted the important role of cellulose-binding region in determining the degree of hydrolysis by cellulases.

Enhanced rhizosphere competence of Trichoderma viride grown in solid state fermentation on corn cob residue

A process has been disclosed in the present investigation for the production of a formulation of mycopesticide with enhanced shelf life of Trichoderma viride. A comparative evaluation of talc-based and corn cob formulations in the form of seed coat and soil treatment brought to light that the soil treatment significantly enhanced the plant growth performance of pea, green gram and pigeon pea. Among the two formulations, the corn cob formulation proved to be better as the rhizosphere competence of corn cob formulation was superior to that of talc formulation. Our results suggest that corn cob residue is a better substrate owing to high cellulase and spore production. Solid-state fermentation in batch cultures. The biocontrol ability of both formulations was tested against Fusarium in Cajanus species and it was found that the disease incidence was reduced by 86% when the corn cob formulation was given as soil application.

Making Sustainable Biofuels and Sunscreen from Corncobs To Introduce Students to Integrated Biorefinery Concepts and Techniques

To inspire upper-division undergraduate students to gain a deeper understanding of biorefinery, an experiment related to biofuels and lignin-based sunscreen products from corncob was performed in multiple offerings of a summer-semester class. Specifically, corncobs were pretreated with 1% H2SO4 to obtain hemicellulose hydrolysates, which were detoxified, and followed with oleaginous yeast fermentation to yield microbial lipids. The microbial lipids were chemically transesterified into biodiesel in situ by an alkali catalyst. Subsequently, dilute acid-pretreated corncob residue was enzymatically saccharified to release glucose for ethanol production by separation hydrolysis and fermentation. Finally, the resultant lignin from the cellulosic ethanol production was valorized to make sunscreen. The main objectives of this work are to introduce students to integrated biorefinery concepts and techniques so that they can learn how to obtain added-value products from waste materials and to evoke students’ awarene...

Heterologous expression of Talaromyces emersonii cellobiohydrolase Cel7A in Trichoderma reesei increases the efficiency of corncob residues saccharification.

Improve the hydrolysis efficiency of the Trichoderma reesei cellulase system by heterologously expressing cellobiohydrolase Cel7A (Te-Cel7A) from the thermophilic fungus Talaromyces emersonii. Te-Cel7A was expressed in T. reesei under control of the cdna1 promoter and the generated transformant QTC14 could successfully secrete Te-Cel7A into the supernatant using glucose as carbon source. The recombinant Te-Cel7A had a temperature optimum at 65°C and an optimal pH of 5, which were similar to those from the native host. The culture supernatant of QTC14 exhibited a 28.8% enhancement in cellobiohydrolase activity and a 65.2% increase in filter paper activity relative to that of the parental strain QP4. Moreover, the QTC14 cellulase system showed higher thermal stability than that of the parental strain QP4. In the saccharification of delignified corncob residue, the cellulose conversion of QTC14 showed 13.9% higher than that of QP4 at the end of reaction. The thermophilic fungus-derived cellulases could be efficiently expressed by T. reesei and the recombinant cellulases had potential applications for biomass conversion.

Differential reinforcement of enzymatic hydrolysis by adding chemicals and accessory proteins to high solid loading substrates with different pretreatments.

High dosage of enzyme is required to achieve effective lignocellulose hydrolysis, especially at high-solid loadings, which is a significant barrier to large-scale bioconversion of lignocellulose. Here, we screened four chemical additives and three accessory proteins for their effects on the enzymatic hydrolysis of various lignocellulosic materials. The effects were found to be highly dependent on the composition and solid loadings of substrates. For xylan-extracted lignin-rich corncob residue, the enhancing effect of PEG 6000 was most pronounced and negligibly affected by solid content, which reduced more than half of enzyme demand at 20% dry matter (DM). Lytic polysaccharide monooxygenase enhanced the hydrolysis of ammonium sulfite wheat straw pulp, and its addition reduced about half of protein demand at the solid loading of 20% DM. Supplementation of the additives in the hydrolysis of pure cellulose and complex lignocellulosic materials revealed that their effects are tightly linked to pretreatment strategies.

Performances of Several Solvents on the Cleavage of Inter- and Intramolecular Linkages of Lignin in Corncob Residue.

The performances of solvents, including γ-butyrolactone (GBL), γ-valerolactone (GVL), tetrahydrofuran (THF), ethyl acetate (EAC), 2-methyltetrahydrofuran (2-MeTHF), and the corresponding mixtures with H2 O, on the cleavage of inter- and intramolecular linkages of lignin in corncob residue were investigated. At 200 °C, miscible cosolvents (H2 O-GBL, H2 O-GVL, and H2 O-THF) exhibited much better efficiency for lignin dissolution than that of both immiscible cosolvents (H2 O-EAC and H2 O-2-MeTHF) and pure solvents. The synergetic effect between H2 O and organic solvent significantly promoted the breakage of intermolecular linkages between C6-O-H of amorphous cellulose and lignin. GBL and THF solvents preferentially dissolved lignin with H and G units, whereas GVL, EAC, and 2-MeTHF solvents exhibited high selectivity for the dissolution of lignin with S and G units. In addition to dissolution, the intramolecular β-O-4 linkage in lignin could be selectively cleaved in H2 O-GBL cosolvent, whereas the β-O-4, α-O-4, and β-5 linkages were cleaved in H2 O-EAC, H2 O-THF, and H2 O-2-MeTHF cosolvents. At 300 °C, the breakage of the β-γ bond prior to β-O-4 in H2 O-GBL, H2 O-THF, H2 O-EAC, and H2 O-2-MeTHF produced 4-ethylphenol and 4-ethylguaiacol selectively (accounting for ≈70 % of the total identified monophenols), whereas the α-1 bond was preferably broken in H2 O-GVL to form guaiacol (accounting for ≈75 % of the total identified monophenols).

Enhancing Biogas Production from Lime Soaked Corn Cob Residue

This study assessed the impact of lime (Ca(OH) 2 ) soaking pretreatment on biomass digestibility and potential of biogas production compare to untreated corn cob. Corn cob was soaked for different time of incubation, 7, 15, and 30 days. Scanning electron micrograph perceived destruction in the morphology of treated corn cob. The highest cumulative biogas of 360.5, 305.4, 218.6 NmL/gVS was obtained from 30, 15, 7 days pretreated corn cob respectively, which was 2-times higher than the cumulative biogas produced from the untreated corn cob 115.1 NmL/gVS. The best result for the methane yield (136.8 NmL/gVS) was obtained for 30 days soaking. The present study suggested that soaking with Ca(OH) 2 for longer time is effective for increasing digestibility of agriculture waste biomass and improving biogas production.

Production of highly efficient cellulase mixtures by genetically exploiting the potentials of Trichoderma reesei endogenous cellulases for hydrolysis of corncob residues

BackgroundTrichoderma reesei is one of the most important fungi utilized for cellulase production. However, its cellulase system has been proven to be present in suboptimal ratio for deconstruction of lignocellulosic substrates. Although previous enzymatic optimization studies have acquired different types of in vitro synthetic mixtures for efficient lignocellulose hydrolysis, production of in vivo optimized cellulase mixtures by industrial strains remains one of the obstacles to reduce enzyme cost in the biofuels production from lignocellulosic biomass.ResultsIn this study, we used a systematic genetic strategy based on the pyrG marker to overexpress the major cellulase components in a hypercellulolytic T. reesei strain and produce the highly efficient cellulase mixture for saccharification of corncob residues. We found that overexpression of CBH2 exhibited a 32-fold increase in the transcription level and a comparable protein level to CBH1, the most abundant secreted protein in T. reesei, but did not contribute much to the cellulolytic ability. However, when EG2 was overexpressed with a 46-fold increase in the transcription level and a comparable protein level to CBH2, the engineered strain QPE36 showed a 1.5-fold enhancement in the total cellulase activity (up to 5.8 U/mL FPA) and a significant promotion of saccharification efficiency towards differently pretreated corncob residues. To assist the following genetic manipulations, the marker pyrG was successfully excised by homologous recombination based on resistance to 5-FOA. Furthermore, BGL1 was overexpressed in the EG2 overexpression strain QE51 (pyrG-excised) and a 11.6-fold increase in BGL activity was obtained. The EG2–BGL1 double overexpression strain QEB4 displayed a remarkable enhancement of cellulolytic ability on pretreated corncob residues. Especially, a nearly complete cellulose conversion (94.2%) was found for the delignified corncob residues after 48 h enzymatic saccharification.ConclusionsThese results demonstrate that genetically exploiting the potentials of T. reesei endogenous cellulases to produce highly efficient cellulase mixtures is a powerful strategy to promote the saccharification efficiency, which will eventually facilitate cost reduction for lignocellulose-based biofuels.

Production of the versatile cellulase for cellulose bioconversion and cellulase inducer synthesis by genetic improvement of Trichoderma reesei

BackgroundThe enzymes for efficient hydrolysis of lignocellulosic biomass are a major factor in the development of an economically feasible cellulose bioconversion process. Up to now, low hydrolysis efficiency and high production cost of cellulases remain the significant hurdles in this process. The aim of the present study was to develop a versatile cellulase system with the enhanced hydrolytic efficiency and the ability to synthesize powerful inducers by genetically engineering Trichoderma reesei.ResultsIn our study, we employed a systematic genetic strategy to construct the carbon catabolite-derepressed strain T. reesei SCB18 to produce the cellulase complex that exhibited a strong cellulolytic capacity for biomass saccharification and an extraordinary high β-glucosidase (BGL) activity for cellulase-inducing disaccharides synthesis. We first identified the hypercellulolytic and uracil auxotrophic strain T. reesei SP4 as carbon catabolite repressed, and then deleted the carbon catabolite repressor gene cre1 in the genome. We found that the deletion of cre1 with the selectable marker pyrG led to a 72.6% increase in total cellulase activity, but a slight reduction in saccharification efficiency. To facilitate the following genetic modification, the marker pyrG was successfully removed by homologous recombination based on resistance to 5-FOA. Furthermore, the Aspergillus niger BGLA-encoding gene bglA was overexpressed, and the generated strain T. reesei SCB18 exhibited a 29.8% increase in total cellulase activity and a 51.3-fold enhancement in BGL activity (up to 103.9 IU/mL). We observed that the cellulase system of SCB18 showed significantly higher saccharification efficiency toward differently pretreated corncob residues than the control strains SDC11 and SP4. Moreover, the crude enzyme preparation from SCB18 with high BGL activity possessed strong transglycosylation ability to synthesize β-disaccharides from glucose. The transglycosylation product was finally utilized as the inducer for cellulase production, which provided a 63.0% increase in total cellulase activity compared to the frequently used soluble inducer, lactose.ConclusionsIn summary, we constructed a versatile cellulase system in T. reesei for efficient biomass saccharification and powerful cellulase inducer synthesis by combinational genetic manipulation of three distinct types of genes to achieve the customized cellulase production, thus providing a viable strategy for further strain improvement to reduce the cost of biomass-based biofuel production.