Emerging trends in high-solids enzymatic saccharification of lignocellulosic feedstocks for developing an efficient and industrially deployable sugar platform

High-solids saccharification of non-pretreated citrus peels through tailored cellulase

Citrus peels, characterized by their low lignin and high sugar content, have been drawing increasing attention as a valuable lignocellulosic biomass with significant potential in biorefinery. Notably, in this study, the citrus waste was found to be enzymatically accessible without any pretreatment. Moreover, to promote the high-solids saccharification of the citrus peels, a tailored cellulase cocktail was formulated by response surface methodology (RSM), along with a fed-batch strategy aiming to obtain a high substrate loading. The study resulted in an optimized cellulase cocktail (7.08 U/g DM of β-glucosidase, 164.17 U/g DM of hemicellulase, 47.38 mg/g DM of sophorolipid, and 64.68 mg/g DM of Tween 80) and achieved solids loading of 22 % with a total sugar concentration of 123.84 g/L, corresponding to a yield of 93.12 % (65.28 % in batch operation). These findings provided essential validation for the efficient utilization of citrus waste, ensuring them promising potential as feedstock for sugar platforms.

A review of nanotechnology in enzyme cascade to address challenges in pre-treating biomass

Nanotechnology has become a revolutionary technique for improving the preliminary treatment of lignocellulosic biomass in the production of biofuels. Traditional methods of pre-treatment have encountered difficulties in effectively degrading the intricate lignocellulosic composition, thereby impeding the conversion of biomass into fermentable sugars. Nanotechnology has enabled the development of enzyme cascade processes that present a potential solution for addressing the limitations. The focus of this review article is to delve into the utilization of nanotechnology in the pretreatment of lignocellulosic biomass through enzyme cascade processes. The review commences with an analysis of the composition and structure of lignocellulosic biomass, followed by a discussion on the drawbacks associated with conventional pre-treatment techniques. The subsequent analysis explores the importance of efficient pre-treatment methods in the context of biofuel production. We thoroughly investigate the utilization of nanotechnology in the pre-treatment of enzyme cascades across three distinct sections. Nanomaterials for enzyme immobilization, enhanced enzyme stability and activity through nanotechnology, and nanocarriers for controlled enzyme delivery. Moreover, the techniques used to analyse nanomaterials and the interactions between enzymes and nanomaterials are introduced. This review emphasizes the significance of comprehending the mechanisms underlying the synergy between nanotechnology and enzymes establishing sustainable and environmentally friendly nanotechnology applications.

Techno-Economic Analysis of 2,3-Butanediol Production from Sugarcane Bagasse

Sugarcane bagasse (SCB) is a significant agricultural residue generated by sugar mills based on sugarcane crop. Valorizing carbohydrate-rich SCB provides an opportunity to improve the profitability of sugar mills with simultaneous production of value-added chemicals, such as 2,3-butanediol (BDO). BDO is a prospective platform chemical with multitude of applications and huge derivative potential. This work presents the techno-economic and profitability analysis for fermentative production of BDO utilizing 96 MT of SCB per day. The study considers plant operation in five scenarios representing the biorefinery annexed to a sugar mill, centralized and decentralized units, and conversion of only xylose or total carbohydrates of SCB. Based on the analysis, the net unit production cost of BDO in the different scenarios ranged from 1.13 to 2.28 US$/kg, while the minimum selling price varied from 1.86 to 3.99 US$/kg. Use of the hemicellulose fraction alone was shown to result in an economically viable plant; however, this was dependent on the condition that the plant would be annexed to a sugar mill which could supply utilities and the feedstock free of cost. A standalone facility where the feedstock and utilities were procured was predicted to be economically feasible with a net present value of about 72 million US$, when both hemicellulose and cellulose fractions of SCB were utilized for BDO production. Sensitivity analysis was also conducted to highlight some key parameters affecting plant economics.

Surfactants facilitated glycerol organosolv pretreatment of lignocellulosic biomass by structural modification for co-production of fermentable sugars and highly reactive lignin

This study reported that surfactants could facilitate the organosolv pretreatment of lignocellulosic biomass (LCB) to produce fermentable sugars and highly active lignin. Under the optimized conditions, the surfactant-assisted glycerol organosolv (saGO) pretreatment achieved 80.7% delignification with a retention of 93.4% cellulose and 83.0% hemicellulose. The saGO pretreated substrate exhibited an excellent enzymatic hydrolyzability, achieving 93% of glucose yield from the enzymatic hydrolysis at 48 h. Structural analysis showed that the saGO lignin contained rich β-O-4 bondings with less repolymerization and lower phenolic hydroxyl groups, thus forming highly reactive lignin fragments. The analysis evidenced that the surfactant graft the lignin by structural modification, which was responsible for the excellent substrate hydrolyzability. The co-production of fermentable sugars and organosolv lignin almost recovered a gross energy (87.2%) from LCB. Overall, the saGO pretreatment holds a lot of promise for launching a novel pathway towards lignocellulosic fractionation and lignin valorization.

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.

Liquid hot water pretreatment combined with high-solids enzymatic hydrolysis and fed-batch fermentation for succinic acid sustainable processed from sugarcane bagasse

In order to sustainable process of bio-succinic acid (SA), response surface methodology (RSM) was applied to optimize liquid hot water pretreatment pretreatment of sugarcane bagasse (SCB), followed by high-solids enzymatic hydrolysis of pretreated residual that without washing, then the hydrolysates and partial pretreatment liquid were used as carbon sources for SA fermentation. Results showed that the highest sugars yield could be achieved at pretreatment conditions of temperature 186 °C, time 25 min and solid-to-liquid ratio 0.08; enzymatic digestion the pretreated residuals at 20 % (w/v) solid content via enzymes reconstruction and fed-batch strategy, the obtained sugars reached to 121 g/L; by controlling the nutrition and conditions of the fermentation process, most of the C5 and C6 sugars in the hydrolysate and pretreatment liquid were converted into SA with a conversion rate high to 280 mg/g SCB. This study can provide a novel clue for clean and efficient biorefining of chemicals.

Increasing extracellular cellulase activity of the recombinant Saccharomyces cerevisiae by engineering cell wall-related proteins for improved consolidated processing of carbon neutral lignocellulosic biomass

Sustainable bioproduction usingcarbon neutral feedstocks, especially lignocellulosic biomass, has attracted increasing attention due to concern over climate change and carbon reduction. Consolidated bioprocessing (CBP) of lignocellulosic biomass using recombinantyeast of Saccharomyces cerevisiaeis a promising strategy forlignocellulosic biorefinery. However, the economic viability is restricted by low enzyme secretion levels.For more efficient CBP, MIG1_spsc01isolated from the industrial yeast which encodes the glucose repression regulator derivative was overexpressed. Increased extracellular cellobiohydrolase (CBH) activity was observed with unexpectedly decreased cell wall integrity. Further studies revealed that disruption ofCWP2, YGP1, andUTH1,which are functionally related toMIG1_spsc01, also enhanced CBH secretion. Subsequently, improved cellulase production was achieved by simultaneous disruption ofYGP1and overexpression ofSED5, which remarkably increased extracellular CBH activity of 2.2-fold over the control strain. These results provide a novel strategy to improve the CBP yeast for bioconversion of carbon neutral biomass.

A tailored bifunctional carbon catalyst for efficient glycosidic bond fracture and selective hemicellulose fractionation

This study proposed a mild chlorination-sulfonation approach to synthesize magnetic carbon acid bearing with catalytic SO₃H and adsorption Cl bifunctional sites on polydopamine coating. The catalysts exerted good textural structure and surface chemical properties (i.e., porosity, high specific surface area of >70 m²/g, high catalytic activity with 0.86-1.1 mmol/g of SO₃H sites and 0.8%-1.9% of Cl sites, and abundant hydrophilic functional groups), rendering a maximum cellobiose adsorption efficiency of ∼40% within 6 h. Moreover, the catalysts had strong fracture characteristics on different α-/β-glycosidic bonds with 85.4%-93.9% of disaccharide conversion, while selectively fractionating hemicellulose from wheat straw with 64.3% of xylose yield and 93.4% of cellulose retention. Due to the stable interaction between parent polydopamine support with Fe core and functional groups, the catalysts efficiently recovered by simple magnetic separation had good reusability with minimal losses in catalytic activity.