Green approach to produce xylo-oligosaccharides and glucose by mechanical-hydrothermal pretreatment

Efficient and facile biphasic pretreatment for corn stover fractionation with comprehensive utilization of cellulose, xylan and lignin

Developing a mild and efficient pretreatment technique to fully utilize lignocellulosic biomass remains a challenge. In this work, a biphasic system with 2-phenoxyethanol (EPH) organic solvent and phosphotungstic acid (PTA) aqueous solution was employed to pretreat corn stover. The prominent synergistic effect between EPH and PTA was revealed to play a key role in the fractionation of corn stover. The excellent separation efficiency with 88.55 % cellulose retention, 85.02 % xylan removal, and 86.68 % lignin removal was achieved under mild pretreatment conditions. The 62.18 % of xylose in aqueous phase, and 83.44 % of lignin from organic phase were recovered after the EPH/PTA biphasic pretreatment. Furthermore, the solid residue was digested with high enzymatic glucose yield of 92.69 %, and the xylose was oxidated with xylonic acid yield of 50.06 %. Meanwhile, the high-performance lignin-based films were manufactured by using the recovered lignin. This study presented a promising way for high-value utilization of lignocellulosic biomass.

Integrated production of xylose and docosahexaenoic acid from hemicellulose and cellulose in corncob

Exploring efficient and comprehensive utilization of agricultural waste to produce high value-added products has been global research hotspot. In this study, a novel process for integrated production of xylose and docosahexaenoic acid (DHA) from hemicellulose and cellulose in corncob was developed. Corncob was treated with dilute H2SO4 at 121 °C for 1 h and xylose was readily produced with a recovery yield of 79.35 %. The corncob residue was then subject to alkali pretreatment under optimized conditions of 0.1 g NaOH/g dry solid, 60 °C for 2 h, and the contents of cellulose, hemicellulose, and lignin in the resulting residue were 87.49 %, 7.58 % and 2.31 %, respectively. The cellulose in the residue was easily hydrolyzed by cellulase, yielding 74.87 g/L glucose with hydrolysis efficiency of 77.02 %. Remarkably, the corncob residue hydrolysate supported cell growth and DHA production in Schizochytrium sp. ATCC 20888 well, and the maximum biomass of 32.71 g/L and DHA yield of 4.63 g/L were obtained, with DHA percentage in total fatty acids of 36.89 %. This study demonstrates that the corncob residue generated during xylose production, rich in cellulose, can be effectively utilized for DHA production by Schizochytrium sp., offering a cost-effective and sustainable alternative to pure glucose.

Combined pretreatment of malic acid and kraft pulping for the production of fermentable sugars and highly active lignin

The separation and utilization of cellulose, hemicellulose, and lignin in lignocellulosic biorefineries present significant challenges. This study proposes a pretreatment method for biomass refining by combining acid and kraft pulping. Firstly, the biomass was pretreated by malic acid, resulting in the isolation of xylo-oligosaccharides (XOS) with a yield of 86.26 % with optimized conditions of 180 °C, 1 wt% concentration, 40 min. Secondly, a mixture of 12.98 wt% NaOH and 1.043 wt% Na2S is employed to achieve lignin removal efficiency up to 63.42 %. Physical refinement techniques are then applied to enhance the enzyme digestion efficiency of cellulose, resulting in an increase from 55.03 % to 91.4 % for efficient cellulose conversion. The reacted samples exhibit a lignin composition rich in β-O-4 ether bonds, facilitating their high-value utilization. The results indicated that the combined pretreatment approach demonstrates high efficiency in separating cellulose, hemicellulose, and lignin while obtaining XOS, highly active lignin, and enzyme-digested substrates.

Comprehensive reutilization of Glycyrrhiza uralensis residue by extrusion-biological pretreatment for coproduction of flavonoids, cellulase, and ethanol

A continuous chemical-free green approach was investigated for the comprehensive reutilization of all components in herbal extraction residues (HERs), taking Glycyrrhiza uralensis residue (GUR) as an example. The GUR structural changes induced by mechanical extrusion which improve the specific surface area and enzyme accessibility of GUR. With 3 % pretreated GUR loading of high-tolerance Penicillium oxalicum G2. The reducing sugar yield of 11.45 g/L was achieved, along with an 81.06 % in situ enzymatic hydrolysis. Finally, 8.23 g/L bioethanol (0.40 g/g total sugar) was produced from GUR hydrolysates after 24 h fermentation of Pichia stipitis G32. The amount of functional medicinal ingredients extracted from GUR after hydrolysis (39.63 mg/g) was 37.69 % greater than that of un-pretreated GUR. In total, 1.49 g flavonoids, 294.36 U cellulase, and 14.13 g ethanol could be produced from 100 g GUR using this process, illustrating that this green and efficient process has the potential for industrial production.

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.

Selective separation of hemicellulose from poplar by hydrothermal pretreatment with ferric chloride and pH buffer

As an environmentally friendly lignocellulosic biomass separation technology, hydrothermal pretreatment (HP) has a strong application prospect. However, the low separation efficiency is a main factor limiting its application. In this study, the poplar components were separated using HP with ferric chloride and pH buffer (HFB). The optimal conditions were ferric chloride concentration of 0.10 M, reaction temperature of 150 °C, reaction time of 15 min and pH 1.9. The separation of hemicellulose was increased 34.03 % to 77.02 %. The pH buffering resulted in the highest cellulose and lignin retention yields compared to ferric chloride pretreatment (FC). The high efficiency separation of hemicellulose via HFB pretreatment inhibited the degradation of xylose. The hydrolysate was effectively reused for five times. The fiber crystallinity index reached 60.05 %, and the highest C/O ratio was obtained. The results provide theoretical support for improving the efficiency of HP and promoting its application.

The Potential of Xylooligosaccharides as Prebiotics and Their Sustainable Production from Agro-Industrial by-Products

In recent years, concerns about a good-quality diet have increased. Food supplements such as prebiotics have great nutritional and health benefits. Within the diverse range of prebiotics, xylooligosaccharides (XOs) show high potential, presenting exceptional properties for the prevention of systemic disorders. XOs can be found in different natural sources; however, their production is limited. Lignocellulosic biomasses present a high potential as a source of raw material for the production of XOs, making the agro-industrial by-products the perfect candidates for production on an industrial scale. However, these biomasses require the application of physicochemical pretreatments to obtain XOs. Different pretreatment methodologies are discussed in terms of increasing the production of XOs and limiting the coproduction of toxic compounds. The advance in new technologies for XOs production could decrease their real cost (USD 25-50/kg) on an industrial scale and would increase the volume of market transactions in the prebiotic sector (USD 4.5 billion). In this sense, new patents and innovations are being strategically developed to expand the use of XOs as daily prebiotics.

Enhancing enzymatic saccharification of sunflower straw through optimal tartaric acid hydrothermal pretreatment

Sunflower straw, a usually neglected and abundant agricultural waste, has great potential for contributing to environmental protection realizing its high-value of valorization if utilizing properly. Because hemicellulose contains amorphous polysaccharide chains, relatively mild organic acid pretreatment can effectively reduce its resistance. Through hydrothermal pretreatment, sunflower straw was pretreated in tartaric acid (1 wt%) at 180 ^oC for 60 min to enhance its reducing sugar recovery. After tartaric acid-assisted hydrothermal pretreatment, 39.9% of lignin and 90.2% of hemicellulose were eliminated. The reducing sugar recovery increased threefold, while the solution could be effectively reused for four cycles. The properties of more porous surface, improved accessibility, and decreased surface lignin area of sunflower straw were observed through various characterizations, which explained the improved saccharide recovery and provided a basis for the mechanism of tartaric acid-assisted hydrothermal pretreatment. Overall, this tartaric acid hydrothermal pretreatment strategy greatly provided new impetus for the biomass refinery.

Enhancing enzymatic hydrolysis of waste sunflower straw by clean hydrothermal pretreatment

Hydrothermal pretreatment is an effective way to change the lignocellulose structure and improve its saccharification. An efficient hydrothermal pretreatment of sunflower straw was conducted when the severity factor (LogR0) was 4.1. 60.4% of xylan and 36.5% of lignin were removed at 180 ℃ for 120 minutes with a solid-to-liquid ratio of 1:15. A series of characterizations (such as X-ray diffraction, Fourier Transform infrared spectroscopy, scanning electron microscopy, chemical component analysis, cellulase accessibility) proved that hydrothermal pretreatment destroyed sunflower straw surface structure, enlarged its pores, and enhanced the accessibility to cellulase (371.2 mg/g). After the enzymatic saccharification of treated sunflower straw for 72 h, 68.0% yield of reducing sugar and 61.8% yield of glucose were achieved, and 4.0 g/L xylo-oligosaccharide was obtained in the filtrate. Overall, this easy-to-operate and green hydrothermal pretreatment could effectively destroy the surface barrier of lignocellulose, help remove lignin and xylan, and increase the enzymatic hydrolysis efficiency.

Hydrothermal pretreatment for the production of prebiotic oligosaccharides from tobacco stem

Tobacco stem is an abundant and inexpensive renewable source to produce prebiotics by circular economy. In this study, hydrothermal pretreatments were evaluated on the release of xylooligosaccharides (XOS) and cello-oligosaccharides (COS) from the tobacco stem by a central composite rotational design associated with response surface methodology to evaluate the effects of temperature (161.72 to 218.3 °C) and solid load (SL) (2.93 to 17.07%). XOS were the main compounds released to the liquor. Desirability function was performed to maximize the production of XOS and minimize the effects of release of monosaccharides and degradation compounds. The result indicated yield of 96% w[XOS]/w[xylan] for 190 °C-2.93% SL. The highest value for COS and total oligomers content (COS + XOS) was 6.42 g/L and 17.7 g/L, respectively, for 190 °C-17.07% SL. The mass balance for the best yield XOS condition predicted 132 kg of XOS (X2-X6) from 1000 kg of tobacco stem.

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.

High solids loading pretreatment: The core of lignocellulose biorefinery as an industrial technology - An overview

Pretreatment is the first and most determinative, yet the least mature step of lignocellulose biorefinery chain. The current stagnation of biorefinery commercialization indicates the barriers of the existing pretreatment technologies are needed to be unlocked. This review focused on one of the core factors, the high lignocellulose solids loading in pretreatment. The high solids loading of pretreatment significantly reduces water input, energy requirement, toxic compound discharge, solid/liquid separation costs, and carbon dioxide emissions, improves the titers of sugars and biproducts to meet the industrial requirements. Meanwhile, lignocellulose feedstock after high solids loading pretreatment is compatible with the existing logistics system for densification, packaging, storage, and transportation. Both the technical-economic analysis and the cellulosic ethanol conversion performance suggest that the solids loading in the pretreatment step need to be further elevated towards an industrial technology and the effective solutions should be proposed to the technical barriers in high solids loading pretreatment operations.

Recent advances on physical technologies for the pretreatment of food waste and lignocellulosic residues

The complete deployment of a bio-based economy is essential to meet the United Nations' Sustainable Development Goals from the 2030 Agenda. In this context, food waste and lignocellulosic residues are considered low-cost feedstocks for obtaining industrially attractive products through biological processes. The effective conversion of these raw materials is, however, still challenging, since they are recalcitrant to bioprocessing and must be first treated to alter their physicochemical properties and ease the accessibility to their structural components. Among the full pallet of pretreatments, physical methods are recognised to have a high potential to transform food waste and lignocellulosic residues. This review provides a critical discussion about the recent advances on milling, extrusion, ultrasound, and microwave pretreatments. Their mechanisms and modes of application are analysed and the main drawbacks and limitations for their use at an industrial scale are discussed.

Efficient co-production of xylooligosaccharides and glucose from lignocelluloses by acid/pentanol pretreatment: Synergetic role of lignin removal and inhibitors

A novel technology for co-production of xylooligosaccharides (XOS) and glucose from Monterey pine sawdust and wheat straw was introduced using dilute acid (DA)/pentanol pretreatment. Effects of pretreatment severity (PS), lignin removal, and inhibitors with byproduct concentrations on XOS production were investigated. Optimal identified conditions (PS: 3.71; 170 °C, 45 min) resulted in maximum XOS of 48.65 % (pine sawdust) and 46.85 % (wheat straw), due to appropriate lignin removal (pine sawdust, 88.5 %; wheat straw, 89.7 %) and formation of small amounts of inhibitors and byproducts. Enzymatic hydrolysis of optimal pretreated solid residues yielded 88.65 % and 93.34 % glucose in pine sawdust and wheat straw, respectively. Biomass characterization revealed that DA/pentanol pretreatment enhanced porosity and pore size along with removal of amorphous fractions in both samples, thereby increasing cellulose accessibility and glucose yield. This study demonstrated lignin removal and low formation of inhibitors and byproducts, effectively enhancing XOS and glucose production from lignocellulosic biomass.

Valorization of bamboo shoot shell waste for the coproduction of fermentable sugars and xylooligosaccharides

In this work, hydrothermal pretreatment (autohydrolysis) was coupled with endo-xylanase enzymatic hydrolysis for bamboo shoot shell (BSS) to produce glucose and valuable xylooligosaccharides (XOS) rich in xylobiose (X2) and xylotriose (X3). Results showed that the enzymatic hydrolysis efficiency of pretreated BSS residue reached 88.4% with addition of PEG during the hydrolysis process. To enrich the portions of X2–X3 in XOS, endo-xylanase was used to hydrolyze the XOS in the prehydrolysate, which was obtained at the optimum condition (170°C, 50 min). After enzymatic hydrolysis, the yield of XOS reached 25.6%, which contained 76.7% of X2–X3. Moreover, the prehydrolysate contained a low concentration of fermentation inhibitors (formic acid 0.7 g/L, acetic acid 2.6 g/L, furfural 0.7 g/L). Based on mass balance, 32.1 g of glucose and 6.6 g of XOS (containing 5.1 g of X2-X3) could be produced from 100.0 g of BSS by the coupled technology. These results indicate that BSS could be an economical feedstock for the production of glucose and XOS.

Sustainable Food Systems: The Case of Functional Compounds towards the Development of Clean Label Food Products

The addition of natural components with functional properties in novel food formulations confers one of the main challenges that the modern food industry is called to face. New EU directives and the global turn to circular economy models are also pressing the agro-industrial sector to adopt cradle-to-cradle approaches for their by-products and waste streams. This review aims to present the concept of “sustainable functional compounds”, emphasizing on some main bioactive compounds that could be recovered or biotechnologically produced from renewable resources. Herein, and in view of their efficient and “greener” production and extraction, emerging technologies, together with their possible advantages or drawbacks, are presented and discussed. Μodern examples of novel, clean label food products that are composed of sustainable functional compounds are summarized. Finally, some action plans towards the establishment of sustainable food systems are suggested.