Production of xylo-oligosaccharides and ethanol from corncob by combined tartaric acid hydrolysis with simultaneous saccharification and fermentation

Xylooligosaccharides, monosaccharides, and pH-sensitive carbon dots production from Toona sinensis branches using organic acid hydrolysis and hydrothermal treatment

The present study focused on exploring the effectiveness of delignification of the lignocellulosic biomass and pH-controlled organic acid hydrolysis in the cascade utilization of Toona sinensis branches (TB) for the production of xylooligosaccharides (XOS), monosaccharides and carbon dots (CDs). The hydrolysis of delignified TB with propionic acid (PA) resulted in a high XOS yield of 48.1 % at pH 3.0, 170 °C for 60 min. The PA hydrolyzates upon hydrolysis with xylanase yielded 61.2 % XOS. The solid residue from XOS production was subjected to cellulase hydrolysis, resulting in a glucose yield of 87.8 %. Furthermore, CDs were synthesized through a green hydrothermal method using the solid residue from cellulase hydrolysis as a precursor. These CDs exhibited excitation-independent and pH-dependent fluorescence properties. This study demonstrated the integrated utilization of TB for efficient production of XOS, monosaccharides, and pH-sensitive CDs.

Comparison of lactic and propionic acid hydrolysis for production of xylo-oligosaccharides and ethanol from polysaccharides in Toona sinensis branch

Xylan-type hemicellulose hydrolysis by an organic acid solution for the production of xylo-oligosaccharides (XOS) is efficient and eco-friendly, but the effects of different organic acids on XOS production from Toona sinensis branch (TB) biomass is limited. In this work, under the conditions of 170 °C for 60 min, 33.1 % and 38.7 % XOS yields were obtained from polysaccharides present in TB by 2 % lactic acid (LA) and 6 % propionic acid (PA), respectively. Then 77 % of the lignin was removed by hydrogen peroxide-acetic acid pretreatment system, and 39.5 % and 44.7 % XOS yield were obtained from polysaccharides in delignification TB by 2 % LA and 6 % PA, respectively. It was found that PA hydrolysis, especially from delignified TB, resulted in higher XOS yield and purity compared to LA hydrolysis. Moreover, the content of byproducts (xylose, hydroxymethyl-furfural and furfural) in PA hydrolysate was lower. Following the hydrolysis process, the simultaneous saccharification and fermentation of the TB solid residue achieved an ethanol yield of 71.5 %. This work proposed an integrated process to preferentially convert the TB hemicellulose into valuable XOS and then convert the cellulose into ethanol. This process had the advantages of eliminating the need for isolation and purification of xylan, and the potential to obtain multiple products from the same raw material.

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.

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.

Efficient production of xylobiose and xylotriose from corncob by mixed acids and xylanase hydrolysis

Propionic acid (PA) hydrolysis offers a potential pathway for industrial xylooligosaccharide (XOS) production owing to efficiency and simplicity of the process. However, the cost of XOS production needs to be reduced as PA is expensive. This work proposed a strategy of mixed acids hydrolysis, replacing 20% of PA with formic acid (FA), and combined with xylanase hydrolysis to reduce production costs and increase the production of XOS from corncob. The hydrolysis of corncob using mixed FA and PA in a mass ratio of 2:8 produced 61.8% XOS. Xylanase hydrolysis of corncob residue improved XOS yield to 73.1%. Among them, the X2 + X3 yield was as high as 50.6%. Economic evaluation showed that the combined process reduced the XOS production cost by 10.8% compared to PA hydrolysis. The strategy of using FA instead of 20% PA for hydrolysis and enzymatic hydrolysis, with high XOS and monosaccharide yields from corncob, has potential industrial promise.

Xylooligosaccharides: A Bibliometric Analysis and Current Advances of This Bioactive Food Chemical as a Potential Product in Biorefineries' Portfolios

Xylooligosaccharides (XOS) are nondigestible compounds of great interest for food and pharmaceutical industries due to their beneficial prebiotic, antibacterial, antioxidant, and antitumor properties. The market size of XOS is increasing significantly, which makes its production from lignocellulosic biomass an interesting approach to the valorization of the hemicellulose fraction of biomass, which is currently underused. This review comprehensively discusses XOS production from lignocellulosic biomass, aiming at its application in integrated biorefineries. A bibliometric analysis is carried out highlighting the main players in the field. XOS production yields after different biomass pretreatment methods are critically discussed using Microsoft PowerBI® (2.92.706.0) software, which involves screening important trends for decision-making. Enzymatic hydrolysis and the major XOS purification strategies are also explored. Finally, the integration of XOS production into biorefineries, with special attention to economic and environmental aspects, is assessed, providing important information for the implementation of biorefineries containing XOS in their portfolio.

Sodium hydroxide or tetramethylammonium hydroxide modified corncob combined with biodegradable polymers to prepare slow-release carbon source for wastewater denitrification

This study proposed a method to improve the bioavailability of artificially prepared carbon sources for the purpose of wastewater denitrification. This carbon source (named SPC) was prepared by mixing corncobs with poly(3-hydroxybutyrate-3-hydroxyvalerate) (PHBV), where the corncobs were pretreated by NaOH or TMAOH. The results of compositional analysis and FTIR showed that both NaOH and TMAOH degraded lignin, hemicellulose and their connection bonds in corncob, thus increased the cellulose content from 39% to 53% and 55%, respectively. The cumulative carbon release from SPC was about 9.3 mg/g and was consistent with both the first-order kinetic and Ritger-Peppas equation. The released organic matters contained low concentration of refractory components. Correspondingly, it showed excellent denitrification performance in simulated wastewater, and the total nitrogen (TN) removal rate was above 95% (influent NO₃^--N was 40 mg/L) and effluent residual chemical oxygen demand (COD) was less than 50 mg/L.

Co-production process optimization and carbon footprint analysis of biohydrogen and biofertilizer from corncob by photo-fermentation

In this study, corncob was taken as substrate, the co-production process of biohydrogen and biofertilizer by photo-fermentation was investigated and its carbon footprint analysis was conducted to evaluate the carbon transfer pathway. Biohydrogen was produced by photo-fermentation, and the hydrogen producing residues were immobilized by sodium alginate. Cumulative hydrogen yield (CHY) and nitrogen release ability (NRA) was taken as references, and the effect of substrate particle size on the co-production process was evaluated. Results showed that due to the porous adsorption properties, corncob size of 120 mesh was the optimal one. Under that condition, the highest CHY and NRA were 71.16 mL/g TS and 68.76%, respectively. The carbon footprint analysis indicted that 7.9% carbon element was released as carbon dioxide, 78.3% carbon element was immobilized in the biofertilizer, and 13.8% carbon element was lost. This work is significant of the biomass utilization and clean energy production.

Fast and Selective Degradation of Biomass for Xylose, Glucose and Lignin under Mild Conditions

The conversion of lignocellulose into valuable chemicals has been recognized as the key technology in green chemistry. However, selective degradation of hemicellulose and cellulose with the production of lignin is still a challenge. Therefore, a two-step process has been developed to degrade corncob into xylose and glucose under mild conditions. At first, the corncob was treated with the lower concentration of zinc chloride aqueous solution (30-55 w%) at 95 °C with a short reaction time (8-12 min) and 30.4 w% (selectivity = 89%) of xylose obtained with a solid residue of the composite of cellulose and lignin. Next, the solid residue was treated with a high concentration of zinc chloride aqueous solution (65-85 w%) at 95 °C for about 10 min, and 29.4 w% (selectivity = 92%) of glucose can be obtained. Combining the two steps, the total yield of xylose is 97%, while glucose is 95%. In addition, high pure lignin can be obtained simultaneously, which was confirmed using HSQC studies. Furthermore, for the solid residue of the first-step reaction, a ternary deep eutectic solvent (DES) (choline chloride/oxalic acid/1,4-butanediol, ChCl/OA/BD) has been used to separate the cellulose and lignin efficiently, and high-quality cellulose (Re-C) and lignin (Re-L) were obtained. Furthermore, it provides a simple method to disassemble the lignocellulose for monosaccharides, lignin, and cellulose.

Optimizing tri-acid mixture hydrolysis: An improved strategy for efficient xylooligosaccharides production from corncob

Propionic acid (PA) hydrolysis of corncob for xylooligosaccharides (XOS) production has the advantages of simple operation, high XOS yield and less by-products, but the high price of PA limits its application. Therefore, partially replacing PA with less expensive organic acids, such as formic acid (FA) and acetic acid (AC), may lower the cost of hydrolysis in XOS production. This work investigated the feasibility of XOS production from corncob using a tri-acid mixture of FA, AC and PA. A high XOS yield of 69.1 % was achieved under the optimal FA:PA:AC volume ratio of 1:5:4 at 150 °C for 50 min. Overall, in the XOS production from corncob, it was able to replace 60 % of PA with FA and AC, and decreased the hydrolysis temperature from 170 °C to 150 °C, all of which were important to lower the cost of XOS production using organic acid hydrolysis.