Novel approach for corn straw biorefineries: Production of xylooligosaccharides, lignin and ethanol by nicotinic acid hydrolysis and pentanol pretreatment.

The productive separation and conversion of corn straw offers significant prospects for the economic viability of biorefineries centered on straw resources. In this work, a graded utilization method was proposed to produce xylo-oligosaccharides (XOS), ethanol and lignin from corn straw by nicotinic acid (NA) hydrolysis and water/pentanol pretreatment. A XOS yield of 52.6 % was achieved under optimized conditions of 100 mM NA, 170 °C and 30 min. The solid residue was directly treated with water/pentanol, achieving a lignin removal rate of 79.7 %, and the total XOS yield was improved to 62.6 %. The lignin recovered from pentanol had a high purity of 97.6 %, with high phenolic OH content. Simultaneous saccharification and fermentation of final residue resulted in an ethanol yield of 92.0 %, which yielded 55.3 g/L ethanol. Thus, NA hydrolysis and water/pentanol pretreatment provided an efficient, environmentally friendly approach to fractionate corn straw for the co-production of XOS, ethanol, and lignin.

Efficient production of high concentration monosaccharides and ethanol from poplar wood after delignification and deacetylation.

Efficient enzymatic hydrolysis is required for the production of high concentration monosaccharides and ethanol. The lignin and acetyl group in poplar can limit the enzymatic hydrolysis. However, the effect of delignification combined with deacetylation on the saccharification of poplar for high concentration monosaccharides was not clear. Herein, hydrogen peroxide-acetic acid (HPAA) was used for delignification and sodium hydroxide was used for deacetylation to enhance the hydrolyzability of poplar. Delignification with 60% HPAA at 80 °C could remove 81.9% lignin. Acetyl group was completely removed with 0.5% NaOH at 60 °C. After the saccharification, 318.1 g/L monosaccharides were obtained with a poplar loading of 35% (w/v). After simultaneous saccharification and fermentation, 114.9 g/L bioethanol was gained from delignified and deacetylated poplar. Those results showed the highest monosaccharides and ethanol concentrations in reported research. This developed strategy with a relatively low temperature could effectively improve the production of high concentration monosaccharide and ethanol from poplar.

Efficient co-production of xylo-oligosaccharides and probiotics from corncob by combined lactic acid pretreatment and two-step enzymatic hydrolysis.

Lactic acid (LA) is efficient in xylo-oligosaccharides (XOS) production from poplar. However, the role of LA in XOS production from corncob has not been carefully elucidated, and the co-production of probiotics of Bacillus subtilis from corncob residue has not been reported. In this study, LA pretreatment was combined with enzymatic hydrolysis to produce XOS and monosaccharides from corncob. An XOS yield of 69.9% was obtained from corncob by combining 2% LA pretreatment and xylanase hydrolysis. Yields of 95.6% glucose and 54.0% xylose were obtained from corncob residue via cellulase, and the resulting cellulase hydrolysate was used to culture Bacillus subtilis YS01. The resulting viable count of the strain was 6.4×108 CFU/mL, and the glucose and xylose utilization were 99.0% and 89.8%, respectively. This study demonstrated a green, efficient, and mild process for producing XOS and probiotics from corncob by combining LA pretreatment and enzymatic hydrolysis.

Effect of peracetic acid generation in hydrogen peroxide-acetic acid pretreatment on production of xylooligosaccharides from poplar by organic acid hydrolysis.

Hydrogen peroxide-acetic acid (HPAA) compositions affect the peracetic acid generation and subsequent delignification of lignocellulosic materials. However, the effects of HPAA compositions on lignin removal and poplar hydrolyzability after HPAA pretreatment are not fully elucidated yet. In this work, different volume ratios of HP to AA were used to pretreat poplar, AA and lactic acid (LA) hydrolysis of delignified poplar to produce XOS was compared. Peracetic acid was mainly produced in 1 h of HPAA pretreatment. HPAA with HP to AA ratio of 8:2 (HP8AA2) generated 4.4% peracetic acid and removed 57.7% of lignin at 2 h. Furthermore, XOS production from HP8AA2-pretreated poplar by AA and LA hydrolysis was increased by 97.1% and 14.9% compared to those from raw poplar, respectively. After alkaline incubation, the glucose yield of HP8AA2-AA-pretreated poplar increased from 40.1% to 97.1%. The study results indicated that HP8AA2 was conducive to XOS and monosaccharides production from poplar..

An integrated process using acetic acid hydrolysis and deep eutectic solvent pretreatment for xylooligosaccharides and monosaccharides production from wheat bran.

Organic acid hydrolysis for xylooligosaccharides (XOS) production from lignocelluloses provides the benefits of simple operation, rapid reaction and high XOS yield. However, no literature reported the XOS production from wheat bran (WB) by organic acid hydrolysis. In this paper, acetic acid (AA) hydrolysis was employed to produce XOS from WB. After AA hydrolysis (5 %, v/v, 170 °C, 20 min) of 100 g/L WB, the concentrations of X2, X3, X4, X5 and X6 were 2.4, 5.0, 1.9, 1.9 and 1.4 g/L respectively and the total XOS yield was 62.9 %, which was the highest among the previous researches. The arabinose yield reached 76.1 %. Then, AA-hydrolyzed WB was delignified by deep eutectic solvent (DES) pretreatment and the resulting residue had the glucose and xylose yields of 83.8 % and 54.8 %, respectively. This work offers a productive method for the conversion of WB into XOS, arabinose and glucose by AA hydrolysis and DES pretreatment.

Efficient aerobic fermentation of gluconic acid by high tension oxygen supply strategy with reusable Gluconobacter oxydans HG19 cells.

Gluconic acid is a widely used food and beverage additive, but its production suffers from low efficiency and high cost. In this study, a preferable gluconic acid biosynthesis method without repeated seed culture was proposed and developed using the superior performance of Gluconobacter oxydans. A high oxygen atmosphere satisfying the demand of bio-oxidation increased the productivity of gluconic acid up to ~ 32 g/L/h and the accumulation up to ~ 420 g/L within 24 h of fed-batch fermentation. However, the productivity remarkably decreased when the gluconic acid content was over 350 g/L. Therefore, a continuous fermentation was designed, which in combination with 5 runs of fed-batch fermentation resulted in the final production of 1700 g gluconic acid from 1750 g glucose within 60 h in a 3 L bioreactor. The results suggest that the validity of this model and can enable cost-competitive gluconic acid production in the industry.

Biorefinery Cascade Processing for Converting Corncob to Xylooligosaccharides and Glucose by Maleic Acid Pretreatment.

Corncob as an abundant and low-cost waste resource has received increasing attention to produce value-added chemicals, it is rich in xylan and regarded as the most preferable feedstock for preparing high value added xylooligosaccharides. The use of xylooligosaccharides as core products can cut costs and improve the economic efficiency in biorefinery. In this study, maleic acid, as a non-toxic and edible acidic catalyst, was employed to pretreat corncob and produce xylooligosaccharides. Firstly, the response surface methodology experimental procedure was employed to maximize the yield of the xylooligosaccharides; a yield of 52.9% (w/v) was achieved with 0.5% maleic acid (w/v) at 155 °C for 26 min. In addition, maleic acid pretreatment was also beneficial to enhance the enzymatic hydrolysis efficiency, resulting in an enzymatic glucose yield of 85.4% (w/v) with a total of 10% solids loading. Finally, a total of 160 g of xylooligosaccharides and 275 g glucose could be produced from 1000 g corncob starting from the maleic acid pretreatment. Overall, a cascade processing for converting corncob to xylooligosaccharides and glucose by sequential maleic acid pretreatment and enzymatic hydrolysis was successfully designed for the corncob wastes utilization.

One-step sodium bisulfate hydrolysis for efficient production of xylooligosaccharides from poplar.

Acid salts have been shown to catalyze xylan hydrolysis selectively and efficiently for xylooligosaccharides (XOS) production while using acid salts that are non-toxic and available as feed additives can avoid separation from resulting XOS-rich hydrolysates. There is no report on XOS production with sodium bisulfate (NaHSO4) hydrolysis, of significance is that NaHSO4 as feed additive does not need to be separated. In this work, NaHSO4 hydrolysis was firstly employed to produce XOS from poplar. XOS yield of 42.7% was reached under optimal conditions of 0.04 mol/L NaHSO4, 170 °C and 60 min. After hydrogen peroxide/acetic acid and sodium hydroxide treatments of NaHSO4-pretreated poplar, high yields of glucose (92.0%) and xylose (91.3%) were obtained at a low cellulase dose of 5 FPU/g dry mass. NaHSO4 hydrolysis was a novel strategy to prepare XOS efficiently with simple operation steps, and XOS-rich hydrolysates could be potentially used as feed additives without NaHSO4 separation.

Lignin removal improves xylooligosaccharides production from poplar by acetic acid hydrolysis.

Organic acid hydrolysis is a potential method for xylooligosaccharides (XOS) production from lignocelluloses. However, the effect of lignin content on XOS production using organic acid hydrolysis remains unclear. In this work, the effect of delignification on XOS production from poplar by acetic acid (AC) hydrolysis was investigated. Hydrogen peroxide-acetic acid (HPAC) pretreatment catalyzed by 0-200 mM H2SO4 (HPAC0-HPAC200) removed 21.6-86.5% of lignin in poplar. HPAC pretreatment increased the xylan accessibility to AC solution, thus increasing the xylan removal during AC hydrolysis. An appropriate delignification (61.7%) resulted in the highest XOS yield of 37.4% by AC hydrolysis, increased by 29.9% compared to the optimal XOS yield (28.8%) from raw poplar. After alkaline post-incubation, the glucose yield of poplar residue rose from 57.1% to 78.6%. This work developed a delignification process to efficiently improve XOS and monosaccharides production from poplar.

Two-step acetic acid/sodium acetate and xylanase hydrolysis for xylooligosaccharides production from corncob.

At present, xylooligosaccharides (XOS) from corncob using acid-base conjugate system has not been reported. In this study, XOS production from corncob by two-step acetic acid/sodium acetate (AC/SA) conjugate system hydrolysis and xylanase hydrolysis was optimized, and monosaccharides were subsequently produced from corncob residues by cellulase hydrolysis. The XOS of 19.9 g/L was obtained from corncob (10%, w/v) using 0.15 M AC/SA hydrolysis at a molar ratio of 3.0 at 170 °C for 60 min, followed by xylanase hydrolysis. The second-step AC/SA hydrolysis of hydrolyzed corncob (10%, w/v) produced 3.1 g/L of XOS. Finally, the maximum XOS yield of 74.8% (based on xylan in corncob) was achieved, which is the highest yield among yields reported previously. The purity of XOS was high, whereas the contents of by-products were very low. This work presents a novel and promising strategy for co-production of XOS and monosaccharides from corncob without xylan isolation and purification.

An integrated process to produce prebiotic xylooligosaccharides by autohydrolysis, nanofiltration and endo-xylanase from alkali-extracted xylan.

Alkali-extracted xylan from lignocellulosics is a promising feedstock for production of prebiotic xylooligosaccharides (XOS). An integrated process was established combining autohydrolysis, nanofiltration and xylanase hydrolysis. Results show that after autohydrolysis 48.37% of xylan was degraded into oligomers and dissolved into the autohydrolysate, of which 57.83% were XOS. By-products and xylose were removed by nanofiltration with discontinuous diafiltration, while high recovery yields of XOS (84.15%) and xylan (87.45%) were obtained. High yields of XOS were obtained by adding xylanase to the autohydrolysates; after enzymatic hydrolysis an XOS yield of 96-98% was obtained. The enzymatic hydrolysates showed positive prebiotic effects on B. adolescentis with an increase in cell concentration by 4.8-fold after fermentation for 24 h. The main products were short-chain fatty acids with carbon balanced during the whole fermentation process. This integrated strategy resulted in a final XOS conversion of 41.22% contrasted to the initial xylan in raw alkali-extracted xylan.

Continuous Bioconversion of Oleuropein from Olive Leaf Extract to Produce the Bioactive Product Hydroxytyrosol Using Carrier-Immobilized Enzyme.

Feasibility and stability were evaluated of a continuous multi-batch process for converting oleuropein (OLE) from olive leaf extract to the bioactive product hydroxytyrosol (HT). Carrier beads made of three different materials (calcium alginate, chitosan with deacetylated α-chitin nanofibers (DEChN), or porous ceramic) were investigated for morphology, thermogravimetric, sorption, and viscoelastic properties. Enzymatic hydrolysis of OLE conducted in a packed bed bioreactor containing cellulase immobilized to carrier beads yielded OLE degradation rates of ~ 90% and an average HT yield of ~ 70% over 20 batches. Ultimately, inorganic porous ceramic beads were less costly and exhibited superior performance relative to organic carriers and thus were deemed most suitable for industrial-scale HT production. Systems utilizing enzyme immobilization within packed bed reactors hold promise for achieving efficient production of valuable bioproducts from discarded biomass materials.

Production of xylooligosaccharides and monosaccharides from poplar by a two-step acetic acid and peroxide/acetic acid pretreatment.

BACKGROUND: Populus (poplar) tree species including hybrid varieties are considered as promising biomass feedstock for biofuels and biochemicals production due to their fast growing, short vegetative cycle, and widely distribution. In this work, poplar was pretreated with acetic acid (AC) to produce xylooligosaccharides (XOS), and hydrogen peroxide-acetic acid (HPAC) was used to remove residual lignin in AC-pretreated poplar for enzymatic hydrolysis. The aim of this work is to produce XOS and monosaccharides from poplar by a two-step pretreatment method. RESULTS: The optimal conditions for the AC pretreatment were 170 °C, 5% AC, and 30 min, giving a XOS yield of 55.8%. The optimal HPAC pretreatment conditions were 60 °C, 2 h, and 80% HPAC, resulting in 92.7% delignification and 87.8% cellulose retention in the AC-pretreated poplar. The two step-treated poplar presented 86.6% glucose yield and 89.0% xylose yield by enzymatic hydrolysis with a cellulases loading of 7.2 m/g dry mass. Very high glucose (93.8%) and xylose (94.6%) yields were obtained with 14.3 mg cellulases/g dry mass. Both Tween 80 and ß-glucosidase enhanced glucose yield of HPAC-pretreated poplar by alleviating the accumulation of cellobiose. Under the optimal conditions, 6.9 g XOS, 40.3 g glucose, and 8.9 g xylose were produced from 100 g poplar. CONCLUSIONS: The AC and HPAC pretreatment of poplar represented an efficient strategy to produce XOS and fermentable sugars with high yields. This two-step pretreatment was a recyclable benign and advantageous scheme for biorefinery of the poplar into XOS and monosaccharides.

Physicochemical transformation of rice straw after pretreatment with a deep eutectic solvent of choline chloride/urea.

This study focused on the pretreatment with deep eutectic solvent of choline chloride (ChCl)/urea mixtures on rice straw and its chemical fractions of holocellulose, α-cellulose, and acid-insoluble-lignin (AIL). The pretreatment of ChCl/urea was significantly affected by the treated temperature prior to the treated time, and 130°C and 4h was an optimum condition for ChCl/urea pretreatment. The separation capacity of ChCl/urea on the chemical fractions was in an order of AIL (22.87%)> hemicellulose and amorphous cellulose (16.71%)>α-cellulose (9.60%). ChCl/urea had a higher selective solubility on lignin. The solubility of the whole fractionation of rice straw affected by ChCl/urea was a combination of solubilization on cellulose, hemicellulose and lignin. ChCl/urea pretreatment increased crystallinity index (CrI) of rice straw residue and α-cellulose, while had no obvious influence on CrI of holocellulose. The effect of structural properties of rice straw residue on enzymatic hydrolysis was also explored.

[Simultaneous determination of organic acids and saccharides in lactic acid fermentation broth from biomass using high performance liquid chromatography].

Abstract: A high performance liquid chromatographic method for the simultaneous determination of organic acids and saccharides in lactic acid fermentation broth from biomass was developed. A Bio-Rad Aminex HPX-87H column was used at 55 degrees C. The mobile phase was 5 mmol/L sulfuric acid solution at a flow rate of 0.6 mL/min. The samples were detected by a refractive index detector (RID). The results showed that six organic acids and three saccharides in fermentation broth were completely separated and determined in 17 min. The linear correlation coefficients were above 0.999 8 in the range of 0.15-5.19 g/L. Under the optimized conditions, the recoveries of the organic acids and saccharides in Rhizopus oryzae fermentation broth at two spiked levels were in the range of 96.91%-103.11% with the relative standard deviations (RSDs, n = 6) of 0.81%-4.61%. This method is fast and accurate for the quantitative analysis of the organic acids and saccharides in microbial fermentation broths.

[Determination of main degradation products of lignin using reversed-phase high performance liquid chromatography].

An analytical method using reversed-phase high performance liquid chromatography (RP-HPLC) was developed for the separation and quantitative determination of main degradation products of lignin (4-hydroxybenzoic acid, vanillic acid, syringic acid, 4-hydroxybenzaldehyde, vanillin and syringaldehyde) during the steam exploded pretreatment for corn stovers. The separation was carried out on a C18 column with the mobile phase of acetonitrile-water (containing 1.5% acetic acid) at 30 degrees C at a flow rate of 0.8 mL/min and the detection wavelengths of 254 and 280 nm. Under the optimized conditions, the correlation coefficients of the 6 compounds were between 0.999 9 and 1.000 0. The recoveries of the 6 compounds were all above 96% and the relative standard deviations (n = 6) were less than 2.5%. This method is suitable for the determination of the main degradation products of lignin during the steam exploded pretreatment of lignocellulosics.

[Quantitative determination of xylo-oligosaccharides in xylo-oligosaccharide products with high performance anion-exchange chromatography coupled with pulsed amperometric detection].

A method for the analysis of xylo-oligosaccharides (XOS) in xylo-oligosaccharide products, including xylobiose, xylotriose, xylotetraose, xylopentaose and xylohexaose, was developed using high performance anion-exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD). The retention times of xyloheptaose and xylooctaose were calculated according to the linear relationship between the retention time and the polymerization degree. The separation was performed on a CarboPac PA200 column (250 mm x 3 mm) with a gradient elution of NaOH-NaOAc as the mobile phase. The calibration curves showed good linearity for the xylo-oligosaccharides in the range of 0.804-8.607 mg/L. The detection limits (LODs) and the quantification limits (LOQs) were 0.064 -0.111 mg/L and 0.214 -0.371 mg/L, respectively. Under the optimized conditions, the recoveries of xylo-oligosaccharides at three different spiked levels ranged from 84.29%-118.19%, with the relative standard deviations (RSDs, n = 3) of 0.44%-14.87%. This method is fast and accurate for the quantitative analysis of the xylo-oligosaccharide products.

Improvement of straw surface characteristics via thermomechanical and chemical treatments.

This study focused on effects of thermomechanical treatment, acid hydrolysis and enzymatic hydrolysis of rice straw fibre on its water resistant. Xylose and arabinose yields were 19.97% and 2.55%, respectively with thermomechanical treatment, 24.35% and 3.18% with acid hydrolysis, and 20.11% and 2.73% with enzymatic hydrolysis. The acid treatment dissolved hemicellulose significantly, leading to more fines and more voids in the surface of the rice straw fibre. The fines showed a higher water retention value (WRV) of 137.41% and exhibited higher swelling capacity. An increase in acid loading resulted in the increased WRV. The enzymatic hydrolysis increased the crystallinity of cellulose, but no significant correlation could be found between the chemical component and the water resistance of the rice straw fibre.