Maximum Glucose Yield Research Articles

Enhanced bioethanol production from cassava waste: optimization of thermochemical pretreatment for maximum sugar recovery and characterisation of potential fractions

ABSTRACT Thermochemical pretreatment is an interesting approach for the effective separation of lignocellulosic biomass before fermentation for bioethanol production. This research focused on optimising the thermochemical pretreatment conditions of cassava waste using response surface methodology to predict the glucose yields under the optimal condition. The optimised conditions of 0.045 M of NaOH concentration at 153.59 °C for 48.03 min resulted in the maximum glucose yield of 93.87%. In addition, fermentation process can generate ethanol within a range of solid loading from 10% to 20%. The highest concentration of ethanol was 34.53 ± 0.56 g/L after 72 h, equivalent to ethanol yield of 0.46 g/g. The co-products were also characterised for further utilisation in biorefinery concept. The results of this study confirmed that the thermochemical pretreatment process using the NaOH catalyst could provide high glucose yields, which can be easily converted into bio-based fuels and further valorised of co-products to value-added chemicals.

Cascading Recovery of Added-Value Cocoa Bean Shell Fractions Through Autohydrolysis Treatments

AbstractIn this work, an autohydrolysis treatment was applied to cocoa bean shells (CBS) to obtain different potentially added-value fractions rich in phenolic compounds with antioxidant potential and oligosaccharides with potential prebiotic properties. The final residue was enzymatically treated to deliver sugars that can undergo fermentation-based biotransformation. This hydrothermal pretreatment was assessed for maximum temperatures (Tmax) between 120 to 200 °C and severities (S0) between 1.1 and 3.4. The highest oligosaccharide concentration (5.5 g/L) was achieved at S0 of 3.4. The increase of S0 during the process allowed to increase the recovery of interesting bioactive compounds, achieving a maximum TPC and antioxidant activity of 2.8 g/L and 17178.5 µmol Fe2+/L, respectively, when the Tmax reached 200 °C. However, at this temperature, a significant amount of degradation products such as organic acids and HMF was already formed, and a compromise temperature of 160 °C was chosen for further tests. It was possible to obtain a maximum glucose yield of 71% when the pretreated solids were enzymatically hydrolysed. Hence, the use of autohydrolysis, avoiding the use of toxic chemicals, has proved to be a sustainable alternative to obtain different CBS fractions with interesting composition to be potentially employed in multiple sectors.

Enhancing fermentable sugar production from sugarcane bagasse through surfactant-assisted ethylene glycol pretreatment and enzymatic hydrolysis: Reduced temperature and enzyme loading

In this study, an efficient coupling surfactant to ethylene glycol pretreatment (EG) and enzymatic hydrolysis of sugarcane bagasse (SCB) was proposed to enhance fermentable sugar production with lower pretreatment energy consumption and reduced enzyme loading. Under optimized conditions, 5 % Tween 80-assisted EG pretreatment of SCB achieved 80.5 % delignification while retaining cellulose (91.6 %) and hemicellulose (81.6 %) content. This led to an enhanced glucose yield of 81.3 %, compared to 65.1 % without Tween 80. The addition of Tween 80 to pretreatment modified residual lignin through etherification, reduced phenolic hydroxyl groups and enhanced hydrophilicity by 23.7 % and 9.4 %, respectively, compared to the lignin sample without Tween 80. Consequently, this modification alleviated non-productive adsorption between lignin and enzymes, improving substrate hydrolyzability. Moreover, when 4.5 % Triton-X 100 was introduced during the hydrolysis of Tween 80-assisted EG-pretreated substrates, a maximum glucose yield of 91.8 % and xylose yield of 92.6 % were achieved. Energy and enzyme cost analyses revealed a reduction of 35 % in pretreatment energy consumption and a 58.8 % decrease in enzyme costs, thanks to the synergistic action of surfactants in EG pretreatment and enzymatic hydrolysis. Overall, integrating surfactants into pretreatment and enzymatic hydrolysis holds promise for highly efficient conversion of SCB into fermentable sugars in enzyme-mediated lignocellulosic biorefineries.

A novel Ruminiclostridium thermocellum cellulase system enhances cellulosic saccharification by elimination of cellobiose feedback inhibition

The Ruminiclostridium thermocellum cellulosome system is one of the most efficient cellulase systems in nature. The main hydrolysis product of cellulosic saccharification by R. thermocellum was cellobiose, which served as a strong feedback inhibitor to the cellulosome. In this study, R. thermocellum M3, which directly hydrolyzes cellulosic biomass into monosaccharides, was used to degrade cellobiose to investigate the kinetic characteristics of cellobiose degradation. Moreover, the transcriptomic characteristics of strain M3 under cellobiose and Avicel culture conditions were compared. The results indicated that strain M3 was able to grow and hydrolyze cellobiose under cellobiose concentrations higher than 20 g/L. The best growth performance and glucose production were obtained under 12 g/L cellobiose. Compared with that of Avicel, cellobiose had greater β-glucosidase activity under cellobiose culture, with a maximum glucose yield of 767.97±19.13 mg/g cellobiose. The transcription results indicated that R. thermocellum M3 resisted the feedback inhibition of cellobiose by regulating genes encoding β-glucosidase, cellobiose phosphorylase and ABC transporters. The high glucose yield of strain M3 was closely related to the expression of the bglX gene. In addition, the gene related to the chemotactic pathway of strain M3 also increased its perception and adaptation to cellobiose.

Fractionation of oil palm fronds using ethanol-assisted deep eutectic solvent: Influence of ethanol concentration on enhancing enzymatic saccharification and lignin β-O-4 content

Numerous fractionation methods have been developed in recent years for separating components such as cellulose, hemicellulose, and lignin from lignocellulosic biomass wastes. Deep eutectic solvents (DES) have recently been widely investigated as captivating green solvents for biomass fractionation. However, most acidic-based deep eutectic solvent fractionation produces condensed lignin with low β-O-4 content. Besides, most DESs exhibit high viscosity, which results in poor mass transfer properties. This study aimed to address the challenges above by incorporating ethanol into the deep eutectic solvent at various concentrations (10–50 wt%) to fractionate oil palm fronds at a mild condition, i.e., 80 °C, 1 atm. Cellulose residues fractionated with ethanol-assisted deep eutectic solvent showed a maximum glucose yield of 85.8% when 20 wt% of ethanol was incorporated in the deep eutectic solvent, significantly higher than that achieved by pure DES (44.8%). Lignin extracted with ethanol-assisted deep eutectic solvent is lighter in color and higher in β-O-4 contents (up to 44 β-O-4 per 100 aromatic units) than pure DES-extracted lignin. Overall, this study has demonstrated that incorporating ethanol into deep eutectic solvents could enhance the applicability of deep eutectic solvents in the complete valorization of lignocellulosic biomass. Highly enzymatic digestible cellulose-rich solid and β-O-4-rich lignin attained from the fractionation could serve as sustainable precursors for the production of biofuels.

1-Ethyl-3-methylimidazolium acetate pretreatment for maximizing reducing sugar recovery from mixed cabbage residue.

Vegetable waste, including mixed cabbage residue (MCR), is considered a promising raw material for bioenergy production because of its high lignocellulosic component. In this study, the pretreatment of MCR by ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) was optimized based on response surface methodology. The optimal condition for MCR pretreatment was determined at 55.8°C, with a reaction of 2.65h and liquid-solid ratio of 4.60:1 v/w. Hydrolysis of pretreated MCR from optimal pretreatment conditions generated a maximum glucose yield of 156.65 ± 7.66mg/g MCR. Untreated and pretreated MCRs were successfully characterized by scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The pretreated MCR exhibited increased clear pores and incomplete structure. Moreover, compared with untreated biomass, decreased lignin, decreased hemicellulose, increased surface area, and cellulose crystallinity were observed. Thus, [Emim][OAc] pretreatment is a promising alternative approach for higher glucose production from MCR.

Sulfomethylation reactivity enhanced the Fenton oxidation pretreatment of bamboo residues for enzymatic digestibility and ethanol production.

Bamboo is considered a renewable energy bioresource for solving the energy crisis and climate change. Dendrocalamus branddisii (DB) was first subjected to sulfomethylation reaction at 95°C for 3h, followed by Fenton oxidation pretreatment at 22°C for 24h. The synergistic effect of combined pretreatment dramatically improved enzymatic digestibility efficiency, with maximum yield of glucose and ethanol content of 71.11% and 16.47g/L, respectively, increased by 4.7 and 6.11 time comparing with the single Fenton oxidation pretreatment. It was found that the hydrophobicity of substrate, content of surface lignin, degree of polymerization, and specific surface area have significant effects on the increase of enzymatic saccharification efficiency. It also revealed that sulfomethylation pre-extraction can improve the hydrophilicity of lignin, leading to the lignin dissolution, which was beneficial for subsequent Fenton pretreatment of bamboo biomass. This work provides some reference for Fenton oxidation pretreatment of bamboo biomass, which can not only promote the utilization of bamboo in southwest China, but also enhances the Fenton reaction in the bamboo biorefinery.

Environmental impact of 5-hydroxymethylfurfural production from cellulosic sugars using biochar-based acid catalyst

In this study, HMF was successfully synthesized from a range of cellulosic sugars, utilizing sustainable acidic biochar derived from cassava rhizome (CR). Various acid precursors such as sulfuric acid (H2SO4),p-toluenesulfonic acid (TsOH), and ferric chloride (FeCl3) were chosen. Acids grafted biochar were carried out through a facile hydrothermal method. HMF production was performed at 175 °C for 0.5 h using 10 % of the acidic biochar catalyst in water to isopropanol (i-PrOH) mixture ratio of 1:4. The maximum HMF yields of fructose (53.29 wt%), glucose (2.94 wt%), and cellulose (0.38 wt%) could be achieved over 600-H2SO4, 700-FeCl3, and 400-H2SO4catalysts, respectively. Moreover, the recyclability of the acidic biochar catalysts could distinguish more than five times without significant loss of activity. Remarkably, the life cycle assessment (LCA) and cost analysis of the HMF production process indicated that the future sustainable industrial production of HMF could be realizedinvolving the 600-TsOH catalyst.

Unprecedented glucose production using auto-catalytic hydrothermal hydrolysis of lignocellulosic biomass with no catalyst addition

We propose a novel and simple glucose production method involving autocatalytic hydrothermal hydrolysis of biomass without catalyst additives. This method consists of air-oxidation at a relatively lower temperature than that of the conventional method and subsequent hydrothermal hydrolysis. Japanese cedar (indigestible softwood) was initially air–oxidized by heating at 180–200 °C for 3 h. This induced the decomposition of a small portion of cellulose in the cedar sample, although 93.4 % of cellulose remained at 200 °C. The functional acidic groups (phenol, lactonic, and carboxy groups) specifically increased during the initial air–oxidation. Following this, the acidic groups autocatalytically accelerated hydrothermal cellulose hydrolysis, resulting in a maximum glucose yield of 139.6 mg/g raw material at a severity factor (R0) of 3.2 × 104.

Novel Strain of Paenibacillus phyllosphaerae CS-148 for the Direct Hydrolysis of Raw Starch into Glucose: Isolation and Fermentation Optimization.

The conventional process for converting starch to glucose is energy-intensive. To lower the cost of this process, a novel strain of Paenibacillus phyllosphaerae CS-148 was isolated and identified, which could directly hydrolyze raw starch into glucose and accumulate glucose in the fermentation broth. The effects of different organic and inorganic nitrogen sources, the culture temperature, the initial pH, and the agitation speed on the yield of glucose were optimized through the one-factor-at-a-time method. Nine factors were screened by Plackett-Burman design, and three factors (raw corncob starch, yeast extract and (NH4)2SO4) had significant effects on glucose yield. Three significant factors were further optimized using Box-Behnken design. Under the optimized fermentation conditions (raw corncob starch 40.4 g/L, yeast extract 4.27 g/L, (NH4)2SO4 4.39 g/L, KH2PO4 2 g/L, MgSO4`7H2O 2 g/L, FeSO4`7H2O 0.02 g/L, NaCl 2 g/L, KCl 0.5 g/L, inoculums volume 4%, temperature 35 °C, agitation rate 150 rpm, and initial pH 7.0), the maximum glucose yield reached 17.32 ± 0.46 g/L, which is 1.33-fold compared to that by initial fermentation conditions. The maximum conversion rate and glucose productivity were 0.43 ± 0.01 g glucose/g raw corn starch and 0.22 ± 0.01 g/(L·h), respectively. These results implied that P. phyllosphaerae CS-148 could be used in the food industry or fermentation industry at a low cost.

Efficient co-production of xylo-oligosaccharides and fermentable sugars from sugarcane bagasse by glutamic acid pretreatment

In the production of xylo-oligosaccharides (XOS) by organic acid pretreatment, it is often difficult to isolate organic acids from XOS. Here, an acidic amino acid, glutamic acid (GA), was used to pretreat sugarcane bagasse (SCB) to prepare XOS and fermentable sugars. The effects of GA concentration, hydrolysis temperature, and pretreatment time on the yield and polymerization distribution of XOS were investigated. After hydrolysis by 0.2 M GA at 140 °C for 30 min, the maximum yield of X2-5 was 53.3%, and the concentrations of xylose and furfural were 1.8 g/L and 0.1 g/L, respectively. Meanwhile, GA increased the pore size and porosity of SCB as well as the number of functional groups of amino acid residues, which improved the enzymatic efficiency and the maximum yield of glucose was 95.3%. Thus, GA pretreatment provides a more economical, environmentally friendly and sustainable method for the co-production of XOS and glucose from SCB.

Large Scale Cultivation and Pretreatment Optimization of Freshwater Microalgae Biomass for Bioethanol Production by Yeast Fermentation

The rapid depletion of the world’s fossil fuel reserves and global warming issues have promoted the search for sustainable alternative energy resources. In the present investigation, large-scale cultivation of naturally isolated freshwater microalgae Asterarcys quadricellulare strain was carried out using tertiary treated municipal wastewater as a growth medium in an open HRP pond for bioethanol production. A total of 12.091 kg of dry biomass was obtained at the end of the study. The lipid extracted carbohydrate rich spent microalgae biomass was converted to bioethanol by ethanolic fermentation. The biomass was first pre-treated with different concentrations of H2SO4 and HCL hydrolysis with different temperatures and reaction times. The biomass treated with a 2.0% concentration of H2SO4, showed maximum yields of glucose 308.38 mg.g-1 at 100°C with 180 min reaction time. The hydrolysates derived from the hydrolysis of microalgae biomass were used as a substrate for fermentation by using S. cerevisiae. The obtained bioethanol was analyzed using HPLC and the purity of ethanol was 90%.

Substrate concentration: A more serious consideration than the amount of 5-hydroxymethylfurfural in acid-catalyzed hydrolysis during bioethanol production from starch biomass

5-hydroxymethylfurfural (5-HMF) yield during bioethanol production from starch was determined using spectrophotometry and chromatography. Increasing acid concentration and time favored 5-HMF production with HCl while yield decreased after 45-minute hydrolysis time for HNO3 and H2SO4 hydrolyzed samples. Impacts of glucose (substrate) concentration and produced 5-HMF on bioethanol yield were studied with different sulphuric acid concentrations and different α-amylase and amyloglucosidase activities. A central composite rotational design was utilized to determine the conditions of hydrolysis for optimum glucose production. The results showed that maximum glucose yield occurred at 0.5 M acid concentration and 45-minute hydrolysis time, while maximum yield was achieved at 120 and 280 units of α-amylase and amyloglucosidase activities respectively. It was shown that 5-HMF did not exhibit much inhibition on ethanol yield at low acid concentrations but became pronounced at higher acid concentrations, while high glucose concentrations had a pronounced negative effect on ethanol yield and fermentation efficiency.

Improved glucose yield and concentration of sugarcane bagasse by the pretreatment with ternary deep eutectic solvents and recovery of the pretreated liquid

In this study, a novel ternary deep eutectic solvents (DES) consisting of choline chloride/PEG/hydroxyethyl sulfonic acid (HSA) was developed to effectively improve glucose yield and concentration of sugarcane bagasse, and the conditions of the pretreatment were optimized by response surface method (RSM). Under the optimal conditions, the maximum glucose concentration (GC) could reach 12.39 g/L (HSA concentration 1.34 %, PEG400, 2.3 h, 150 °C), and the maximum glucose yield (GY) was 0.2497 g/g (HSA concentration 1.41 %, PEG400, 2.1 h, 150 °C). Hemicellulose was completely removed, and the maximum lignin removal rate was 86.89 %. After pretreatment, 95 % of the pretreated liquid can be recycled. Finally, the structural and morphological changes of bagasse before and after pretreatment were investigated by scanning electron microscopy (SEM), Fourier Transform infrared analyzer (FT-IR) and X-ray diffraction (XRD).

Ultrasonic‑assisted molten salt hydrates pretreated Eucheuma cottonii residues as a greener precursor for third-generation l-lactic acid production

This study aims to establish an efficient pretreatment method that facilitates the conversion of sugars from macroalgae wastes, Eucheuma cottonii residues (ECRs) during hydrolysis and subsequently enhances l-lactic acid (L-LA) production. Hence, ultrasonic-assisted molten salt hydrates (UMSHs) pretreatment was proposed to enhance the accessibility of ECRs to hydrolyze into glucose through dilute acid hydrolysis (DAH). The obtained hydrolysates were employed as the substrate in producing L-LA by separate hydrolysis and fermentation (SHF). The maximum glucose yield (97.75 %) was achieved using UMSHs pretreated ECRs with 40 wt% ZnCl2 at 80 °C for 2 h and followed with DAH. The optimum glucose to L-LA yield obtained for SHF was 90.08 % using 5 % (w/w) inoculum cell densities of B. coagulans ATCC 7050 with yeast extract (YE). A comparable performance (89.65 %) was obtained using a nutrient combination (lipid-extracted Chlorella vulgaris residues (CVRs), vitamin B3, and vitamin B5) as a partial alternative for YE.

In-depth investigation of the bioethanol and biogas production from organic and mineral acid pretreated sugarcane bagasse: Comparative and optimization studies

Organic acid pretreatment has generated much interest as one of the high potential methods for promoting enzymatic saccharification of lignocellulosic materials. Organic acids are preferred during pretreatment because they are less hazardous than conventional ones and produce less inhibitory fermentation by-products. In the present study, three organic acids (oxalic acid, citric acid, and acetic acid) and inorganic acid (hydrochloric acid) were studied to produce bioethanol and biogas from sugarcane bagasse. An optimization design (Box–Behnken Design (BBD)) among different optimization designs of response surface methodology (RSM) was considered to determine the pretreatment optimum conditions. On this basis, citric acid (CA)pretreatment resulted in maximum glucose yield (7.93 mg/mL) during saccharification. FTIR analysis of the pretreated samples showed that the structure of lignocellulose was changed in higher proportions for the sample pretreated with an organic acid. An increase in cellulose portion and maximum removal of hemicellulose with lower furan generations was observed in organic acid samples. In this study, the maximum solubilization of hemicellulose in hydrochloric acid was also observed due to the abundance of free H+ ions to catalyze the reaction. The ethanol and biogas yield increased by 1.96 and 1.85-fold for citric acid and oxalic acid pretreated sugarcane bagasse, respectively than untreated samples. The present study concluded that oxalic acid and citric acid pretreatment showed the potential to enhance the yield of bioethanol and biogas, respectively. An organic acid in the pretreatment of lignocellulosic biomass can replace traditional methods of using inorganic acids in biorefineries.

Direct conversion of carbon dioxide to glucose using metabolically engineered Cupriavidus necator

Artificial synthesis of glucose, the monomer of starch, from renewable resources and CO2 is a promising method for addressing food crisis and alleviating climate change. Here, the construction of a microbial biocatalyst for glucose production from renewable resources and CO2 was reported. Initially, blocking the glucose catabolic pathway via deletion of glk gene generated a glucose-producing strain of Cupriavidus necator with titers of 24.7, 47.5 and 180.1 mg/L from fructose, glycerol and CO2, respectively. Subsequently, the Entner-Doudoroff pathway and polyhydroxybutyrate biosynthesis pathway were disrupted to further increase glucose accumulation. The maximum glucose titer and yield on biomass from CO2 reached 253.3 mg/L and 91.6 mg/L/OD600, respectively. Finally, the phosphatases that mediate the dephosphorylation of phosphorylated glucose were identified. Overexpression of HAD1 and cbbY2 could enhance glucose titer by 5.5-fold when fructose was used as sole carbon source. This study demonstrates a feasible route for microbial-based synthesis of glucose from CO2.

Ethanol Production from the Mixture of Waste French Fries and Municipal Wastewater via Separate Hydrolysis and Fermentation.

The potential of bioethanol generation using the mixture of waste French fries (WFF) and municipal wastewater (MWW) via separate hydrolysis and fermentation (SHF) was evaluated in this study. The effect of WFF substrate loading (SL, 10%, 16%, and 20%, w/v) on the SHF was also examined. Both glucose production and hydrolysis efficiency increased with increasing of SL from 10 to 16% and the maximum glucose yield of 0.236g glucose/g WFF and hydrolysis efficiency of 91.9% were obtained at SL of 16%. However, the glucose production and hydrolysis efficiency decreased when the SL further increased to 20% due to the inhibition on enzyme caused by higher glucose production. The mixture hydrolysate was then used as feedstock for ethanol fermentation. The maximum ethanol production of 22.69g/L was obtained from SL of 16%. The highest rate of glucose conversion to ethanol was 84.2%. The results demonstrated that the mixture of WFF and MWW could be used for ethanol production by the SHF.

Co-production of xylose, lignin, and ethanol from eucalyptus through a choline chloride-formic acid pretreatment

A choline chloride-formic acid (ChCl-FA) pretreatment followed by enzymatic hydrolysis and fermentation were developed in this work for co-produce bioethanol, xylose, and lignin from eucalyptus. Results showed that ChCl-FA pretreatment can simultaneously degrade the xylan (∼95.2%) and lignin (∼74.4%) in eucalyptus, and obtained the pretreated eucalyptus having high glucan content and a numbers of cracks and holes, which was conducive to follow-up cellulase attacking. The hydrolysis experiments showed the maximum yield of glucose of 100 g eucalyptus was 35.3 g, which was equivalent to 90.3% of glucan in eucalyptus feedstock. The fermentation of enzymatic hydrolysate finally achieved the ethanol yield of 16.5 g, which corresponded to 74.5% theoretical ethanol yield from initial glucan in eucalyptus. In addition, 12.1 g xylose and 23.9 g lignin also could be obtained in pretreated liquid or/and hydrolysis residue, which represented for 61.4% xylan and 80.7% lignin in eucalyptus feedstock, respectively.

Enhancement of glucose production from sugarcane bagasse through an HCl-catalyzed ethylene glycol pretreatment and Tween 80

In this work, an HCl-catalyzed ethylene glycol (EG) pretreatment was exploited for promoting sugar release from sugarcane bagasse (SCB). The results showed that the combination of HCl and EG could remove the xylan (∼100.0%) and lignin (∼61.3%) in SCB together, which finally resulted in the pretreated substrate having a good efficacy for follow-up enzymatic hydrolysis. The maximum glucose yield of this work was 93.9% and obtained after pretreatment at 130 °C for 60 min with 0.5% HCl and 72 h enzymatic digestion. The analysis of various pretreated or un-pretreated SCB indicated that the changes of surface morphology and internal compositions of SCB were the mainly reasons for its hydrolysis efficiency enhancement. The addition of Tween 80 into hydrolysis process could remarkably shorten hydrolysis time and cellulase dosage from 72 h to 36 h and 20 FPU/g substrate to 10 FPU/g substrate, respectively, meanwhile maintaining a relatively high glucose yield (91.4%).