Immobilization of Aspergillus niger cellulase on multiwall carbon nanotubes for cellulose hydrolysis

Phytochemical delivery through nanocarriers: a review

In recent times, phytochemicals encapsulated or conjugated with nanocarriers for delivery to the specific sites have gained considerable research interest. Phytochemicals are mostly plant secondary metabolites which reported to be beneficial for human health and in disease theraphy. However, these compound are large size and polar nature of these compounds, make it difficult to cross the blood-brain barrier (BBB), endothelial lining of blood vessels, gastrointestinal tract and mucosa. Moreover, they are enzymatically degraded in the gastrointestinal tract. Therefore, encapsulation or conjugation of these compounds with nanocrriers could be an alternate way to enhance their bioefficacy by influencing their gastrointestinal stability, rate of absorption and dispersion. This review presents an overview of nanocarriers alternatives which improves therapeutic value and avoid toxicity, by releasing bioactive compounds specifically at target tissues with enhanced stability and bioavailability. Future investigations may emphasize on deciphering the structural changes in nanocarriers during digestion and absorption, the difference between in-vitro and in-vivo digestion simulations, and impact of nanocarriers on the metabolism of phytochemicals.

Fabrication of thermostable and reusable nanobiocatalyst for dye decolourization by immobilization of lignin peroxidase on graphene oxide functionalized MnFe2O4 superparamagnetic nanoparticles

In view of the potential applications of immobilized enzymes, partially purified Lignin Peroxidase (LiP) from Pseudomonas fluorescens LiP-RL5 was immobilized on Graphene Oxide functionalized MnFe₂O₄ nanoparticles (10 nm, synthesized by sol-gel auto-combustion) to fabricate a new hyperactive and thermostable nanobiocatalyst and thereafter characterized by using standard techniques. Immobilized LiP was quite stable at 50 °C with the half-life of 14 h and showed higher tolerance towards various metal ions and solvents than free LiP. Immobilized LiP retained 50% of enzyme activity even after nine consecutive runs. When tested against various textile dyes, the immobilized LiP was found quite effective with higher dye decolourization efficiency (up to 88%) within 1 h of incubation at 30 °C. The results of this research effort confirmed that the immobilization of LiP and fabrication of nanobiocatalyst increase the efficacy, stability, and reusability of the enzyme which could be efficiently utilized under harsh industrial conditions.

Immobilization of enzymes on nanoinorganic support materials: An update

Despite the widespread use in various industries, enzyme's instability and non-reusability limit their applications which can be overcome by immobilization. The nature of the enzyme's support material and method of immobilization affect activity, stability, and kinetics properties of enzymes. Here, we report a comparative study of the effects of inorganic support materials on immobilized enzymes. Accordingly, immobilization of enzymes on nanoinorganic support materials significantly improved thermal and pH stability. Furthermore, immobilizations of enzymes on the materials mainly increased K_m values while decreased the V_max values of enzymes. Immobilized enzymes on nanoinorganic support materials showed the increase in ΔG value, and decrease in both ΔH and ΔS values. In contrast to weak physical adsorption immobilization, covalently-bound and multipoint-attached immobilized enzymes do not release from the support surface to contaminate the product and thus the cost is decreased while the product quality is increased. Nevertheless, nanomaterials can enter the environment and increase health and environmental risks and should be used cautiously. Altogether, it can be predicated that hybrid support materials, directed immobilization methods, site-directed mutagenesis, recombinant fusion protein technology, green nanomaterials and trailor-made supports will be used increasingly to produce more efficient immobilized industrial enzymes in near future.

Current Developments in Lignocellulosic Biomass Conversion into Biofuels Using Nanobiotechology Approach

The conversion of lignocellulosic biomass (LB) to sugar is an intricate process which is the costliest part of the biomass conversion process. Even though acid/enzyme catalysts are usually being used for LB hydrolysis, enzyme immobilization has been recognized as a potential strategy nowadays. The use of nanobiocatalysts increases hydrolytic efficiency and enzyme stability. Furthermore, biocatalyst/enzyme immobilization on magnetic nanoparticles enables easy recovery and reuse of enzymes. Hence, the exploitation of nanobiocatalysts for LB to biofuel conversion will aid in developing a lucrative and sustainable approach. With this perspective, the effects of nanobiocatalysts on LB to biofuel production were reviewed here. Several traits, such as switching the chemical processes using nanomaterials, enzyme immobilization on nanoparticles for higher reaction rates, recycling ability and toxicity effects on microbial cells, were highlighted in this review. Current developments and viability of nanobiocatalysts as a promising option for enhanced LB conversion into the biofuel process were also emphasized. Mostly, this would help in emerging eco-friendly, proficient, and cost-effective biofuel technology.

Black liquor: A potential moistening agent for production of cost-effective hydrolytic enzymes by a newly isolated cellulo-xylano fungal strain Aspergillus tubingensis and its role in higher saccharification efficiency

In the present study, black liquor generated during mild alkali pre-treatment was evaluated as a moistening agent to produce cost effective hydrolytic enzymes using novel cellulo-xylano fungal strain Aspergillus tubingensis M7. The fungus competently produced 21.90 and 22.46 filter paper, 1004 and 1369 endoglucanase, 117 and 142 β-glucosidase and 8188 and 7981 U/g xylanase activity by using modified Mandel & weber's and black liquor medium, respectively. The crude hydrolytic enzymes from black liquor were evaluated for saccharification of pre-treated biomass. Reducing sugar yields (mg/g substrate) and the corresponding saccharification efficiency (%) from rice straw, corncob, sugarcane bagasse and banana stem were 745.50 (86.02; 18 h); 596 (74.50; 24 h); 358.15 (42.98; 24 h) and 245.70 (33.00; 24 h), respectively. Residual biomass compositional analysis revealed that reduced onset temperature, increased activation energy and pre-exponential factor in saccharified biomass as compared to pre-treated and untreated biomass, suggesting their utilization for pyrolysis to obtain value added products.

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.

Synthesis of Dual-Responsive Materials with Reversible and Switchable Phase-Transition Properties for High-Performance Cellulose Enzymatic Hydrolysis

The solid-solid (immobilized cellulase-insoluble cellulose) phase cellulose hydrolysis reaction is significant in cellulosic biomass conversion processes but hindered because of its low efficiency. Herein, a smart temperature-pH dual-responsive material (D-N-N material) was prepared to be used as a carrier for cellulase recovery. This D-N-N material could undergo reversible and switchable transitions between solution, hydrogel, and solid phases. The following results were demonstrated: 1) the hydrolytic degree of this strategy could be as high as that of free cellulase in buffer solution; 2) the cellulase could be encapsulated into the D-N-N hydrogel without significant leaching and most of the cellulase activity was retained after recycling for at least 10 batches; and 3) more than 95 % of the glucose inside the hydrogel could be extracted during the hydrogel-solid transition within 1 h, which can assist in the high-efficiency separation of cellulase from glucose. The results suggested that this strategy provides a feasible platform for efficient cellulose hydrolysis and could be applied to other bio-derived reactions.

Nanomaterials Utilization in Biomass for Biofuel and Bioenergy Production

The world energy production trumped by the exhaustive utilization of fossil fuels has highlighted the importance of searching for an alternative energy source that exhibits great potential. Ongoing efforts are being implemented to resolve the challenges regarding the preliminary processes before conversion to bioenergy such as pretreatment, enzymatic hydrolysis and cultivation of biomass. Nanotechnology has the ability to overcome the challenges associated with these biomass sources through their distinctive active sites for various reactions and processes. In this review, the potential of nanotechnology incorporated into these biomasses as an aid or addictive to enhance the efficiency of bioenergy generation has been reviewed. The fundamentals of nanomaterials along with their various bioenergy applications were discussed in-depth. Moreover, the optimization and enhancement of bioenergy production from lignocellulose, microalgae and wastewater using nanomaterials are comprehensively evaluated. The distinctive features of these nanomaterials contributing to better performance of biofuels, biodiesel, enzymes and microbial fuel cells are also critically reviewed. Subsequently, future trends and research needs are highlighted based on the current literature.

Optimization and characterization of oligosaccharides production from citrus peel waste resource using Aspergillus niger 1805

Oligosaccharides have many growth-promoting properties for crops and are effective for fighting off various diseases in agriculture. Producing oligosaccharides from waste fruit peel by using food microorganisms will be a potential approach to provide the high-value products for sustainable development of green agriculture. Aspergillus niger 1805 was isolated from citrus peel and identified by internal transcribed spacer (ITS1-ITS4) sequencing. A. niger 1805 grew well only with waste citrus peel (WCP) as the sole medium. >50% WCP was degraded into oligosaccharides by fermentation with A. niger at 37 °C, pH 5.0 and 4 mM Ca²⁺ within 72 h, and oligosaccharide yield rate of >40%. Most oligosaccharides were in the form of Nano-size particles [10-500 nm]. Kolmogorov-Smirnov Goodness of Fit Test (KS test) showed that the distribution of the oligosaccharide micro-particles fitted a lognormal model (p > .05). Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS) analysis showed that the oligosaccharides were mainly comprised of glucose polymer with degrees of polymerization (DP) of 4-17. A. niger 1805 is a potential tool to produce oligosaccharides from WCP.

Layered Co-Immobilization of β-Glucosidase and Cellulase on Polymer Film by Visible-Light-Induced Graft Polymerization

Exploring a suitable immobilization strategy to improve catalytic efficiency and reusability of cellulase is of great importance to lowering the cost and promoting the industrialization of cellulose-derived bioethanol. In this work, a layered structure with a thin PEG hydrogel as the inner layer and sodium polyacrylate (PAANa) brush as the outer layer was fabricated on low density polyethylene (LDPE) film by visible-light-induced graft polymerization. Two enzymes, β-glucosidase (BG) and cellulase, were separately coimmobilized onto this hierarchical film. As supplementary to cellulase for improving catalytic efficiency, BG was in situ entrapped into the inner PEG hydrogel layer during the graft polymerization from the LDPE surface. After graft polymerization of sodium acrylate on the PEG hydrogel layer was reinitiated, cellulase was covalently attached on the outer PAANa brush layer. Owing to the mild reaction condition (visible-light irradiation and room temperature), the immobilized BG could retain a high activity after the graft polymerization. The immobilization did not alter the optimal pH and temperature of BG or the optimal temperature of cellulase. However, the optimal pH of cellulase shifts to 5.0 after immobilization. Compared with the original activity of single cellulase system and isolated BG/cellulase immobilization system, the dual-enzyme system exhibited 82% and 20% increase in catalytic activity, respectively. The dual-enzyme system could maintain 93% of carboxymethylcellulose sodium salt (CMC) activity after repeating 10 cycles of hydrolysis and 89% of filter paper activity after 6 cycles relative to original activity, exhibiting excellent reusability. This layer coimmobilization system of BG and cellulase on the polymer film displays tremendous potential for practical application in a biorefinery.

Nano-immobilized cellulases for biomass processing with application in biofuel production

Several researches have focused on the enzymatic pretreatment of lignocellulose biomass to produce fermentable sugars that can lead to ethanol production thus facilitating pathways for sustainable biofuel production. Enzymes are fundamental to the pretreatment process, however, are required in larger quantities during pretreatment process thus influencing biofuel production cost. Immobilization of enzymes to a suitable support/matrix could enhance its stability, and reusability thus containing cost. This chapter focuses on developing an advanced technology for immobilizing enzymes to nanomaterials; variety of nanomaterials used for immobilization, nature of enzyme/protein nanomaterial interactions, methods of enzyme immobilization, and factors affecting mode of interaction for achieving hydrolysis of microcrystalline cellulose and natural cellulosic substrate. The binding of enzyme (94%) to a nanomaterial was established by spectroscopy techniques. The kinetics study, conducted at optimum pH (pH 4) and temperature (50°C for free and 60°C immobilized enzyme), exhibited improvement in immobilized enzyme properties. The immobilized enzyme retained up to 50% of its enzyme activity in five consecutive cycles. This chapter advocates the use of nano-immobilized enzymes in biomass hydrolysis for biofuel production.

Microbial dynamics for lignocellulosic waste bioconversion and its importance with modern circular economy, challenges and future perspectives

An extensive use of microbial dynamics for utilizing the lignocellulosic wastes has been attributed to their efficiency in bioenergy and bioproducts development as a cost effective high nutritional value. The integration of lignocellulosic waste into the circular economy can scaleup the sustainable bioproducts and bioenergy development. In this review paper, the aim is to describe the existing research efforts on organic lignocellulosic waste, cellulase producing microbes, their potential enzyme, modern circular economy with associated challenges and future perspectives. Presently, it has been reviewed that microbial cellulases have provided treasure bioproducts visions into industrial bioproducts marvels unveiled through lignocellulosic waste cutting-edge microbial explorations. Furthermore, the review focused on new insights of the growing circular economy of lignocellulosic waste used for many bioproducts and bioenergy dealings and explored the emergent lignocellulosic biorefinery approaches which could then be applied to review industrial-scale sustainable economic models for upgraded bioproducts and other production associated problems.

Kinetic and thermodynamic properties of purified alkaline protease from Bacillus pumilus Y7 and non-covalent immobilization to poly(vinylimidazole)/clay hydrogel

The characterization of the hydrogel was performed using Fourier‐transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy. Purified Bacillus pumilus Y7‐derived alkaline protease was immobilized in Poly (vinylimidazole)/clay (PVI/SEP) hydrogel with 95% yield of immobilization. Immobilization decreased the pH optimum from 9 to 6 for free and immobilized enzyme, respectively. Temperature optimum 3°C decreased for immobilized enzyme. The K_m, V_m, and k_cat of immobilized enzyme were 4.4, 1.7, and 7.5‐fold increased over its free counterpart. Immobilized protease retained about 65% residual activity for 16^th reuse. The immobilized protease endured its 35% residual activity in the material after six cycle's batch applications. The results of thermodynamic analysis for casein hydrolysis showed that the ΔG^≠ (activation free energy) and ΔG^≠_E‐T (activation free energy of transition state formation) obtained for the immobilized enzyme decreased in comparison to those obtained for the free enzyme. On the other hand, the value of ΔG^≠_ES (free energy of substrate binding) was observed to have increased. These results indicate an increase in the spontaneity of the biochemical reaction post immobilization. Enthalpy value of immobilized enzyme that was 2.2‐fold increased over the free enzyme indicated lower energy for the formation of the transition state, and increased ΔS^≠ value implied that the immobilized form of the enzyme was more ordered than its free form.

Inulinase immobilization on polyethylene glycol/polypyrrole multiwall carbon nanotubes producing a catalyst with enhanced thermal and operational stability

This paper describes the development of a simple method for mixed non-covalent and covalent bonding of partially purified inulinase on functionalized multiwall carbon nanotubes (f-MWCNTs) with polypyrrole (PPy). The pyrrole (Py) was electrochemically polymerized on MWCNTs in order to fabricate MWCNTs/PPy nanocomposite. Two multiple forms of enzyme were bound to N-H functional groups from PPy and -COO^- from activated MWCNTs to yield a stable MWCNTs/PPy/PEG immobilized preparation with increased thermal stability. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) were used to confirm functionalization of nanoparticles and immobilization of the enzyme. The immobilization yield of 85% and optimal enzyme load of 345 μg protein onto MWCNTs was obtained. The optimum reaction conditions and kinetic parameters were established using the UV-Vis analytical assay. The best functional performance for prepared heterogeneous catalyst has been observed at pH 3.6 and 10, and at the temperatures of 60 and 80ºC. The half-life (t _1/2) of the immobilized inulinase at 60 and 80ºC was found to be 231 and 99 min, respectively. The reusability of the immobilized formulation was evaluated based on a method in which the enzyme retained 50% of its initial activity, which occurred after the eighteenth operation cycle.

Monocrotophos detection with a bienzyme biosensor based on ionic-liquid-modified carbon nanotubes

Acetylcholinesterase (AChE) biosensor technology is widely applied in the detection of organophosphate pesticides in agricultural production via the inhibition of AChE activity by organophosphates. However, the AChE electrode has some drawbacks, such as low stability and high overpotential. Combining the advantages of multiwalled carbon nanotubes (MWCNTs) and ionic liquids, we constructed a novel bienzyme electrode [Cl/iron porphyrin (FePP)-modified MWCNTs/AChE/glassy carbon electrode], which included AChE and mimetic oxidase FePP. In this electrode, FePP is covalently bound to the AChE carrier via ionic liquid for increased electrode sensitivity and stability. Under optimal conditions, this novel biosensor has a monocrotophos detection limit of 3.2 × 10-11 mol/L and good recovery of 89-104%. After 5 weeks of storage at 4 °C, the oxidation current was 97.8% of its original value. The biosensor has high stability and sensitivity for monocrotophos detection and is a promising device for monitoring food safety. Graphical abstract The complete synthesis process of Cl/FePP-MWCNTs/AChE/GCE.

Immobilization of Peroxidase on Functionalized MWCNTs-Buckypaper/Polyvinyl alcohol Nanocomposite Membrane

Surface modified Multi-walled carbon nanotubes (MWCNTs) Buckypaper/Polyvinyl Alcohol (BP/PVA) composite membrane was synthesized and utilized as support material for immobilization of Jicama peroxidase (JP). JP was successfully immobilized on the BP/PVA membrane via covalent bonding by using glutaraldehyde. The immobilization efficiency was optimized using response surface methodology (RSM) with the face-centered central composite design (FCCCD) model. The optimum enzyme immobilization efficiency was achieved at pH 6, with initial enzyme loading of 0.13 U/mL and immobilization time of 130 min. The results of BP/PVA membrane showed excellent performance in immobilization of JP with high enzyme loading of 217 mg/g and immobilization efficiency of 81.74%. The immobilized system exhibited significantly improved operational stability under various parameters, such as pH, temperature, thermal and storage stabilities when compared with free enzyme. The effective binding of peroxidase on the surface of the BP/PVA membrane was evaluated and confirmed by Field emission scanning electron microscopy (FESEM) coupled with Energy Dispersive X-Ray Spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric Analysis (TGA). This work reports the characterization results and performances of the surface modified BP/PVA membrane for peroxidase immobilization. The superior properties of JP-immobilized BP/PVA membrane make it promising new-generation nanomaterials for industrial applications.

Mechanochemical-assisted hydrolysis of pretreated rice straw into glucose and xylose in water by weakly acidic solid catalyst

In this work, carbonaceous materials bearing only weakly acidic COOH and phenolic OH groups were directly prepared by the pyrolysis of lignin and KOH in black liquor generating from rice straw that was pretreated with KOH aqueous solution. The synthesized carbon materials were used for the hydrolysis of cellulose or the alkali pretreated rice straw in water, after mixed ball-milling pretreatment, and provided a high glucose yield of 76.3% for cellulose, high yields of 52.1% glucose and 66.5% xylose for alkali pretreated rice straw, respectively, in 0.015 wt% HCl aqueous solution at 200 °C for 60 min. The weakly acidic catalyst showed good stability and recyclability in the aqueous reaction system. This work provides an efficient process for the hydrolysis of lignocellulose by biomass-derived weakly acidic catalysts in water and should have wide applications in biomass utilization.

Asparaginase conjugated magnetic nanoparticles used for reducing acrylamide formation in food model system

Acrylamide is a potent carcinogen and neurotoxin formed by the Maillard reaction when l-asparagine reacts with starch at high temperature. It is formed in food materials mainly deep fried and bakery products. Enzymatic pretreatment of these food products with asparaginase enzyme leads to reduction in acrylamide. However, enzymatic process is quite expensive due to high cost, low catalytic efficiency as well as problem with enzyme reusability. Present work deals with these problems by exploring l-asparaginase from Bacillus aryabhattai. Asparaginase enzyme was immobilized on APTES modified magnetic nanoparticles. It was found to be more than three-fold increase their thermal stability from free enzyme and retained 90% activity after fifth cycle. The immobilized enzyme also showed better affinity towards its substrate. During pretreatment of asparagine in a starch-asparagine food model system and it was clearly demonstrated that asparaginase nanoconjugates had reduced the formation of acrylamide by more than 90% within 30 min.

Hydrolysis of cellulose using cellulase physically immobilized on highly stable zirconium based metal-organic frameworks

Developing a new cellulase-MOF composite system with enhanced stability and reusability for cellulose hydrolysis was aimed. Physical adsorption strategy was employed to fabricate two cellulase composites, and the activity of composite was characterized by hydrolysis of carboxymethyl cellulose. The NH₂ functionalized UiO-66-NH₂ MOF exhibited higher protein loading than the precursor UiO-66, due to the extra anchor sites of NH₂ groups. The immobilized cellulase showed enhanced thermostability, pH tolerance and lifetime. The maximum activity attained at 55 °C could be kept 85% when used at 80 °C, and the residual activities were 72% after ten cycles and 65% after 30 days storage. The abundant NH₂ and COOH groups of MOF adsorb cellulase and enhance its stability, and the resulted heterogeneity offered the opportunity of recovering composite via mild centrifuge. The findings suggest the promising future of developing cellulase-MOF composite with ultrahigh activities and stabilities for practical application.

Immobilization of Cholesterol Oxidase: An Overview

Background:

Cholesterol oxidases are bacterial oxidases widely used commercially for their application in the detection of cholesterol in blood serum, clinical or food samples. Additionally, these enzymes find potential applications as an insecticide, synthesis of anti-fungal antibiotics and a biocatalyst to transform a number of sterol and non-sterol compounds. However, the soluble form of cholesterol oxidases are found to be less stable when applied at higher temperatures, broader pH range, and incur higher costs. These disadvantages can be overcome by immobilization on carrier matrices.

Methods:

This review focuses on the immobilization of cholesterol oxidases on various macro/micro matrices as well as nanoparticles and their potential applications. Selection of appropriate support matrix in enzyme immobilization is of extreme importance. Recently, nanomaterials have been used as a matrix for immobilization of enzyme due to their large surface area and small size. The bio-compatible length scales and surface chemistry of nanoparticles provide reusability, stability and enhanced performance characteristics for the enzyme-nanoconjugates.

Conclusion:

In this review, immobilization of cholesterol oxidase on nanomaterials and other matrices are discussed. Immobilization on nanomatrices has been observed to increase the stability and activity of enzymes. This enhances the applicability of cholesterol oxidases for various industrial and clinical applications such as in biosensors.

Immobilization of cellulase proteins on zeolitic imidazolate framework (ZIF-8)/polyvinylidene fluoride hybrid membranes

ZIF-8/PVDF hybrid membranes have been applied in cellulase immobilization for the first time, which improves cellulase stability with preserved activity.