Cellulase immobilized by sol–gel entrapment for efficient hydrolysis of cellulose

Enhancing cellulose hydrolysis via cellulase immobilization on zeolitic imidazolate frameworks using physical adsorption

This study investigates the immobilization of cellulase on zeolitic imidazolate frameworks (ZIFs) by physical adsorption, specifically the ZIF-8-NH2 and Fe3O4@ZIF-8-NH2, to enhance enzymatic hydrolysis efficiency. The immobilization process was thoroughly analyzed, including optimization of conditions and characterization of ZIF carriers and immobilized enzymes. The impacts on the catalytic activity of cellulase under various temperatures, pH levels, and storage conditions were examined. Additionally, the reusability of the immobilized enzyme was assessed. Results showed the cellulase immobilized on Fe3O4@ZIF-8-NH2 exhibited a high loading capacity of 339.64 mg/g, surpassing previous studies. Its relative enzymatic activity was found to be 71.39%. Additionally, this immobilized enzyme system demonstrates robust reusability, retaining 68.42% of its initial activity even after 10 cycles. These findings underscore the potential of Fe3O4@ZIF-8-NH2 as a highly efficient platform for cellulase immobilization, with promising implications for lignocellulosic biorefinery.

Cellulase immobilization to enhance enzymatic hydrolysis of lignocellulosic biomass: An all-inclusive review

Cellulase-mediated lignocellulosic biorefinery plays a crucial role in the production of high-value biofuels and chemicals, with enzymatic hydrolysis being an essential component. The advent of cellulase immobilization has revolutionized this process, significantly enhancing the efficiency, stability, and reusability of cellulase enzymes. This review offers a thorough analysis of the fundamental principles underlying immobilization, encompassing various immobilization approaches such as physical adsorption, covalent binding, entrapment, and cross-linking. Furthermore, it explores a diverse range of carrier materials, including inorganic, organic, and hybrid/composite materials. The review also focuses on emerging approaches like multi-enzyme co-immobilization, oriented immobilization, immobilized enzyme microreactors, and enzyme engineering for immobilization. Additionally, it delves into novel carrier technologies like 3D printing carriers, stimuli-responsive carriers, artificial cellulosomes, and biomimetic carriers. Moreover, the review addresses recent obstacles in cellulase immobilization, including molecular-level immobilization mechanism, diffusion limitations, loss of cellulase activity, cellulase leaching, and considerations of cost-effectiveness and scalability. The knowledge derived from this review is anticipated to catalyze the evolution of more efficient and sustainable biocatalytic systems for lignocellulosic biomass conversion, representing the current state-of-the-art in cellulase immobilization techniques.

Influence of elevated pressure and pressurized fluids on microenvironment and activity of enzymes

Enzymes have great potential in bioprocess engineering due to their green and mild reaction conditions. However, there are challenges to their application, such as enzyme extraction and purification costs, enzyme recovery, and long reaction time. Enzymatic reaction rate enhancement and enzyme immobilization have the potential to overcome some of these challenges. Application of high pressure (e.g., hydrostatic pressure, supercritical carbon dioxide) has been shown to increase the activity of some enzymes, such as lipases and cellulases. Under high pressure, enzymes undergo multiple alterations simultaneously. High pressure reduces the bond lengths of molecules of reaction components and causes a reduction in the activation volume of enzyme-substrate complex. Supercritical CO2 interacts with enzyme molecules, catalyzes structural changes, and removes some water molecules from the enzyme's hydration layer. Interaction of scCO2 with the enzyme also leads to an overall change in secondary structure content. In the extreme, such changes may lead to enzyme denaturation, but enzyme activation and stabilization have also been observed. Immobilization of enzymes onto silica and zeolite-based supports has been shown to further stabilize the enzyme and provide resistance towards perturbation under subjection to high pressure and scCO2.

Enhancement of the Catalytic Performance and Operational Stability of Sol-Gel-Entrapped Cellulase by Tailoring the Matrix Structure and Properties

Commercial cellulase Cellic CTec2 was immobilized by the entrapment technique in sol–gel matrices, and sol–gel entrapment with deposition onto magnetic nanoparticles, using binary or ternary systems of silane precursors with alkyl- or aryl-trimethoxysilanes, at different molar ratios. Appropriate tailoring of the sol–gel matrix allowed for the enhancement of the catalytic efficiency of the cellulase biocatalyst, which was then evaluated in the hydrolysis reaction of Avicel microcrystalline cellulose. A correlation between the catalytic activity with the properties of the sol–gel matrix of the nanobiocatalysts was observed using several characterization methods: scanning electron microscopy (SEM), fluorescence microscopy (FM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA/DTA). The homogeneous distribution of the enzymes in the sol–gel matrix and the mass loss profile as a function of temperature were highlighted. The influence of temperature and pH of the reaction medium on the catalytic performance of the nanobiocatalysts as well as the operational stability under optimized reaction conditions were also investigated; the immobilized biocatalysts proved their superiority in comparison to the native cellulase. The magnetic cellulase biocatalyst with the highest efficiency was reused in seven successive batch hydrolysis cycles of microcrystalline cellulose with remanent activity values that were over 40%, thus we obtained promising results for scaling-up the process.

Dual Responsive Molecular-Arm Modified Single Enzyme Molecules for Efficient Cellulose Hydrolysis

Immobilizing cellulase for improving its hydrolysis activity and recyclability is critical for a cost-effective and environment-friendly conversion of cellulosic biomass. However, developing a strategy for achieving a high mass-transfer rate and good separation efficiency between an insoluble cellulose substrate and cellulase remains difficult. Instead of the traditional method, a single-enzyme molecular modification method is used in this study. To modify cellulase and provide it with a temperature-pH dual responsive property, systemized poly (acrylic acid)-polyacrylonitrile (PAA-PAN) molecular arms are used. The modified cellulase could reversibly transform between liquid and solid phases. In the liquid phase, the modified cellulase could adjust its active center, increasing its hydrolysis efficiency and separation efficiency. Cellulase and glucose products could be easily separated in the solid phase, allowing the reuse of cellulase. The results showed that the modified cellulase's hydrolysis efficiency is comparable to that of free cellulase and that the modified enzyme preserved more than 60% of its initial activity after 15 batches of efficient hydrolysis. Thus, the proposed modification route considerably lowers the cost of cellulose enzymatic hydrolysis. This article is protected by copyright. All rights reserved.

Facile Cellulase Immobilisation on Bioinspired Silica

Cellulases are enzymes with great potential for converting biomass to biofuels for sustainable energy. However, their commercial use is limited by their costs and low reusability. Therefore, the scientific and industrial sectors are focusing on finding better strategies to reuse enzymes and improve their performance. In this work, cellulase from Aspergillus niger was immobilised through in situ entrapment and adsorption on bio-inspired silica (BIS) supports. To the best of our knowledge, this green effect strategy has never been applied for cellulase into BIS. In situ entrapment was performed during support synthesis, applying a one-pot approach at mild conditions (room temperature, pH 7, and water solvent), while adsorption was performed after support formation. The loading efficiency was investigated on different immobilisation systems by Bradford assay and FTIR. Bovine serum albumin (BSA) was chosen as a control to optimize cellulase loading. The residual activity of cellulase was analysed by the dinitro salicylic acid (DNS) method. Activity of 90% was observed for the entrapped enzyme, while activity of ~55% was observed for the adsorbed enzyme. Moreover, the supported enzyme systems were recycled five times to evaluate their reuse potential. The thermal and pH stability tests suggested that both entrapment and adsorption strategies can increase enzyme activity. The results highlight that the entrapment in BIS is a potentially useful strategy to easily immobilise enzymes, while preserving their stability and recycle potential.

Current perspective on production and applications of microbial cellulases: a review

The potential of cellulolytic enzymes has been widely studied and explored for bioconversion processes and plays a key role in various industrial applications. Cellulase, a key enzyme for cellulose-rich waste feedstock-based biorefinery, has increasing demand in various industries, e.g., paper and pulp, juice clarification, etc. Also, there has been constant progress in developing new strategies to enhance its production, such as the application of waste feedstock as the substrate for the production of individual or enzyme cocktails, process parameters control, and genetic manipulations for enzyme production with enhanced yield, efficiency, and specificity. Further, an insight into immobilization techniques has also been presented for improved reusability of cellulase, a critical factor that controls the cost of the enzyme at an industrial scale. In addition, the review also gives an insight into the status of the significant application of cellulase in the industrial sector, with its techno-economic analysis for future applications. The present review gives a complete overview of current perspectives on the production of microbial cellulases as a promising tool to develop a sustainable and greener concept for industrial applications.

Cellulose-deconstruction potential of nano-biocatalytic systems: A strategic drive from designing to sustainable applications of immobilized cellulases

Nanostructured materials along with an added value of polymers-based support carriers have gained high interest and considered ideal for enzyme immobilization. The recently emerged nanoscience interface in the form of nanostructured materials combined with immobilized-enzyme-based bio-catalysis has now become research and development frontiers in advance and applied bio-catalysis engineering. With the involvement of nanoscience, various polymers have been thoroughly developed and exploited to nanostructured engineer constructs as ideal support carriers/matrices. Such nanotechnologically engineered support carriers/matrix possesses unique structural, physicochemical, and functional attributes which equilibrate principal factors and strengthen the biocatalysts efficacy for multipurpose applications. In addition, nano-supported catalysts are potential alternatives that can outstrip several limitations of conventional biocatalysts, such as reduced catalytic efficacy and turnover, low mass transfer efficiency, instability during the reaction, and most importantly, partial, or complete inhibition/deactivation. In this context, engineering robust and highly efficient biocatalysts is an industrially relevant prerequisite. This review comprehensively covered various biopolymers and nanostructured materials, including silica, hybrid nanoflower, nanotubes or nanofibers, nanomembranes, graphene oxide nanoparticles, metal-oxide frameworks, and magnetic nanoparticles as robust matrices for cellulase immobilization. The work is further enriched by spotlighting applied and industrially relevant considerations of nano-immobilized cellulases. For instance, owing to the cellulose-deconstruction features of nano-immobilized cellulases, the applications like lignocellulosic biomass conversion into industrially useful products or biofuels, improved paper sheet density and pulp beat in paper and pulp industry, fruit juice clarification in food industry are evident examples of cellulases, thereof are discussed in this work.

Adsorption of Cellulase on Wrinkled Silica Nanoparticles with Enhanced Inter-Wrinkle Distance

Mesoporous silica materials offer a unique opportunity for enzyme immobilization thanks to their properties, such as tuneable pore size, large surface area and easy functionalization. However, a significant enhancement of cellulase enzyme activity entrapped inside the silica pores still represents a challenge. In this work, we immobilized cellulase by adsorption on wrinkled silica nanoparticles (WSNs), obtaining an active and stable biocatalyst. We used pentanol as co-solvent to synthesize WSNs with enhanced inter-wrinkle distance in order to improve cellulase hosting. The physical-chemical and morphological characterization of WSNs and cellulase/WSNs was performed by thermogravimetric (TG), Fourier transform infrared (FT-IR), and transmission electron microscopy (TEM) analyses. The obtained results showed that this matrix generates a favourable microenvironment for hosting cellulase. The results of the catalytic assays and operational stability confirmed the key role of size, morphology and distribution of the pores in the successful outcome of the cellulase immobilization process. The immobilization procedure used allowed preserving most of the secondary structure of the enzyme and, consequently, its catalytic activity. Moreover, the same value of glucose yield was observed for five consecutive runs, showing a high operational stability of the biocatalyst.

Immobilization of Cellulolytic Enzymes in Mesostructured Silica Materials

Mesostructured silica nanoparticles offer a unique opportunity in the field of biocatalysis thanks to their outstanding properties. The tunable pore size in the range of mesopores allows for immobilizing bulky enzyme molecules. The large surface area improves the catalytic efficiency by increasing enzyme loading and finely dispersing the biocatalyst molecules. The easily tunable pore morphology allows for creating a proper environment to host an enzyme. The confining effect of mesopores can improve the enzyme stability and its resistance to extreme pH and temperatures. Benefits also arise from other peculiarities of nanoparticles such as Brownian motion and easy dispersion. Fossil fuel depletion and environmental pollution have led to the need for alternative sustainable and renewable energy sources such as biofuels. In this context, lignocellulosic biomass has been considered as a strategic fuel source. Cellulases are a class of hydrolytic enzymes that convert cellulose into fermentable sugars. This review is intended to survey the immobilization of cellulolytic enzymes (cellulases and β-glucosidase) onto mesoporous silica nanoparticles and their catalytic performance, with the aim to give a contribution to the urgent action required against climate change and its impacts, by biorefineries’ development.

Enhanced Catalytic Performance of Trichoderma reesei Cellulase Immobilized on Magnetic Hierarchical Porous Carbon Nanoparticles

Cellulase from Trichoderma reesei was immobilized by covalent or non-covalent binding onto magnetic hierarchical porous carbon (MHPC) nanomaterials. The immobilization yield and the enzyme activity were higher when covalent immobilization approach was followed. The covalent immobilization approach leads to higher immobilization yield (up to 96%) and enzyme activity (up to 1.35 U mg^-1) compared to the non-covalent cellulase binding. The overall results showed that the thermal, storage and operational stability of the immobilized cellulase was considerably improved compared to the free enzyme. The immobilized cellulose catalyzed the hydrolysis of microcrystalline cellulose up to 6 consecutive successive reaction cycles, with a total operation time of 144 h at 50 °C. The half-life time of the immobilized enzyme in deep eutectic solvents-based media was up to threefold higher compared to the soluble enzyme. The increased pH and temperature tolerance of the immobilized cellulase, as well as the increased operational stability in aqueous and deep eutectic solvents-based media indicate that the use of MHPCs as immobilization nanosupport could expand the catalytic performance of cellulolytic enzymes in various reaction conditions.

Stable cellulase immobilized on graphene oxide@CMC-g-poly(AMPS-co-AAm) hydrogel for enhanced enzymatic hydrolysis of lignocellulosic biomass

This study indicated tailoring efficient polymer-enzyme bioconjugates with superb stability and activity for practical utilization of cellulase enzyme in hydrolyzing lignocellulosic biomass. To this goal, a dual crosslinking (DC) strategy was presented to synthesize novel 3D networks of carboxymethyl cellulose grafted copolymers of 2-acrylamido-2methyl propane sulfonate and acrylamide (CMC-g-poly(AMPS-co-AAm)) hydrogels. Graphene oxide (GO) nano-sheets were utilized as nano-filler and physical cross-linker making H-bondings between polymeric chains to prepare GO@CMC-g-poly(AMPS-co-AAm) networks. The GO content effects on the performance of as-synthesized architectures in conjugation to a model enzyme (PersiCel1) were examined. PersiCel1 immobilization on the GO reinforced hydrogels resulted in noticeable retaining near 60 % of its maximum activity at 90 °C, along with the remarkable enhancement of its specific activity and storage stability. Compared with the free PersiCel1, the immobilized enzyme on the GO containing hydrogels showed 154.8 % increase in conversion of alkalin-treated sugar beet pulp, while the PersiCel1/neat-Hydrogel indicated an increment of 66.7 %, under the same conditions.

Continuous flow biocatalysis

The continuous flow synthesis of active pharmaceutical ingredients, value-added chemicals, and materials has grown tremendously over the past ten years. This revolution in chemical manufacturing has resulted from innovations in both new methodology and technology. This field, however, has been predominantly focused on synthetic organic chemistry, and the use of biocatalysts in continuous flow systems is only now becoming popular. Although immobilized enzymes and whole cells in batch systems are common, their continuous flow counterparts have grown rapidly over the past two years. With continuous flow systems offering improved mixing, mass transfer, thermal control, pressurized processing, decreased variation, automation, process analytical technology, and in-line purification, the combination of biocatalysis and flow chemistry opens powerful new process windows. This Review explores continuous flow biocatalysts with emphasis on new technology, enzymes, whole cells, co-factor recycling, and immobilization methods for the synthesis of pharmaceuticals, value-added chemicals, and materials.

Covalent Immobilization of Cellulase Using Magnetic Poly(ionic liquid) Support: Improvement of the Enzyme Activity and Stability

A magnetic nanocomposite was prepared by entrapment of Fe₃O₄ nanoparticles into the cross-linked ionic liquid/epoxy type polymer. The resulting support was used for covalent immobilization of cellulase through the reaction with epoxy groups. The ionic surface of the support improved the adsorption of enzyme, and a large amount of enzyme (106.1 mg/g) was loaded onto the support surface. The effect of the presence of ionic monomer and covalent binding of enzyme was also investigated. The structure of support was characterized by various instruments such as FT-IR, TGA, VSM, XRD, TEM, SEM, and DLS. The activity and stability of immobilized cellulase were investigated in the prepared support. The results showed that the ionic surface and covalent binding of enzyme onto the support improved the activity, thermal stability, and reusability of cellulase compared to free cellulase.

Tailored sol–gel immobilized lipase preparates for the enzymatic kinetic resolution of heteroaromatic alcohols in batch and continuous flow systems

The EKR of some heteroaromatic secondary ethanols with tailored sol–gel immobilized lipases in batch and continuous-flow reactors was studied. The productivity in continuous-flow mode is higher than in batch mode.

Enzyme Engineering for In Situ Immobilization

Enzymes are used as biocatalysts in a vast range of industrial applications. Immobilization of enzymes to solid supports or their self-assembly into insoluble particles enhances their applicability by strongly improving properties such as stability in changing environments, re-usability and applicability in continuous biocatalytic processes. The possibility of co-immobilizing various functionally related enzymes involved in multistep synthesis, conversion or degradation reactions enables the design of multifunctional biocatalyst with enhanced performance compared to their soluble counterparts. This review provides a brief overview of up-to-date in vitro immobilization strategies while focusing on recent advances in enzyme engineering towards in situ self-assembly into insoluble particles. In situ self-assembly approaches include the bioengineering of bacteria to abundantly form enzymatically active inclusion bodies such as enzyme inclusions or enzyme-coated polyhydroxyalkanoate granules. These one-step production strategies for immobilized enzymes avoid prefabrication of the carrier as well as chemical cross-linking or attachment to a support material while the controlled oriented display strongly enhances the fraction of accessible catalytic sites and hence functional enzymes.

Immobilization of cellulase on a silica gel substrate modified using a 3-APTES self-assembled monolayer

Cellulase was immobilized onto silica gel surfaces pretreated with (3-aminopropyl) triethoxy-silane (3-APTES), and glutaraldehyde (GA) was used as a cross-linker. A carboxymethyl cellulose sodium salt (CMC) solution was used for activity experiments. Protein assay was performed to determine the mass immobilized and compare with free enzyme. Cellulase was successfully demonstrated to be immobilized on the modified silica gel surface, and no detectable amount of enzyme was stripped off during the hydrolysis of the CMC solution. The specific activity of the immobilized cellulase is 7 ± 2 % compared to the similar amount of free cellulase. Significant activity over multiple reuses was observed. The seventh batch achieved 82 % activity of the initial batch, and the fifteenth batch retained 31 %. It was observed that the immobilized cellulase retained 48 % of its initial activity after 4 days, and 22 % even after 14 days.

Enhanced enzymatic hydrolysis of cellulose in microgels

A cellulose-based microgel, where an individual microgel contains approximately one cellulose chain on average, is synthesized via free radical polymerization of a difunctional small-molecule N,N'-methylenebisacrylamide in cellulose solution. This microgelation leads to a low-ordered cellulose, favoring enzymatic hydrolysis of cellulose to generate glucose.

Suitability of magnetic nanoparticle immobilised cellulases in enhancing enzymatic saccharification of pretreated hemp biomass

BACKGROUND

Previous research focused on pretreatment of biomass, production of fermentable sugars and their consumption to produce ethanol. The main goal of the work was to economise the production process cost of fermentable sugars. Therefore, the objective of the present work was to investigate enzyme hydrolysis of microcrystalline cellulose and hemp hurds (natural cellulosic substrate) using free and immobilised enzymes. Cellulase from Trichoderma reesei was immobilised on an activated magnetic support by covalent binding and its activity was compared with that of the free enzyme to hydrolyse microcrystalline cellulose and hemp hurds on the basis of thermostability and reusability.

RESULTS

Up to 94% protein binding was achieved during immobilisation of cellulase on nanoparticles. Successful binding was confirmed using Fourier transform infrared spectroscopy (FTIR). The free and immobilised enzymes exhibited identical pH optima (pH 4.0) and differing temperature optima at 50°C and 60°C, respectively. The K M values obtained for the free and immobilised enzymes were 0.87 mg/mL and 2.6 mg/mL respectively. The immobilised enzyme retained 50% enzyme activity up to five cycles, with thermostability at 80°C superior to that of the free enzyme. Optimum hydrolysis of carboxymethyl cellulose (CMC) with free and immobilised enzymes was 88% and 81%, respectively. With pretreated hemp hurd biomass (HHB), the free and immobilised enzymes resulted in maximum hydrolysis in 48 h of 89% and 93%, respectively.

CONCLUSION

The current work demonstrated the advantages delivered by immobilised enzymes by minimising the consumption of cellulase during substrate hydrolysis and making the production process of fermentable sugars economical and feasible. The activity of cellulase improved as a result of the immobilisation, which provided a better stability at higher temperatures. The immobilised enzyme provided an advantage over the free enzyme through the reusability and longer storage stability properties that were gained as a result of the immobilisation.

Establishing the feasibility of using β-glucosidase entrapped in Lentikats and in sol-gel supports for cellobiose hydrolysis

β-Glucosidases represent an important group of enzymes due to their pivotal role in various biotechnological processes. One of the most prominent is biomass degradation for the production of fuel ethanol from cellulosic agricultural residues and wastes, where the use of immobilized biocatalysts may prove advantageous. Within such scope, the present work aimed to evaluate the feasibility of entrapping β-glucosidase in either sol-gel or in Lentikats supports for application in cellobiose hydrolysis, and to perform the characterization of the resulting bioconversion systems. The activity and stability of the immobilized biocatalyst over given ranges of temperature and pH values were assessed, as well as kinetic data, and compared to the free form, and the operational stability was evaluated. Immobilization increased the thermal stability of the enzyme, with a 10 °C shift to an optimal temperature in the case of sol-gel support. Mass transfer hindrances as a result of immobilization were not significant, for sol-gel support. Lentikats-entrapped glucosidase was used in 19 consecutive batch runs for cellobiose hydrolysis, without noticeable decrease in product yield. Moreover, encouraging results were obtained for continuous operation. In the overall, the feasibility of using immobilized biocatalysts for cellobiose hydrolysis was established.