Improving the stability of cellulase by immobilization on modified polyvinyl alcohol coated chitosan beads

Evaluating the mechanism of soybean meal protein for boosting the laccase-catalyzed of thymol onto lignosulfonate via restraining non-specific adsorption

The control of laccase-catalyzed efficiency often relies on the utilization of modifying enzyme molecules and shielding agents. However, their elevated costs or carcinogenicity led to the inability for large-scale application. To address this concern, we found that a low-cost protein from soybean meal can reduce lignin's ineffective adsorption onto enzymes for improving the efficiency of thymol grafting to lignosulfonate. The results demonstrated that by adding 0.5 mg/mL of additional soybean meal protein, the thymol reaction ratio of the modified lignosulfonate (L-0.5 S) significantly boosted from 18.1 % to 35.0 %, with the minimal inhibitory concentrations of the L-0.5 S against Aspergillus niger dramatically improved from 12.5 mg/mL to 3.1 mg/mL. Multiple characterization methods were employed to better understand the benefit of the modification under the addition of the soybean meal protein. The CO and R1-O group content increased from 20.5 % to 37.8 % and from 65.1 % to 75.5 %, respectively. The proposed potential reaction mechanism was further substantiated by the physicochemical properties. The incorporation of soybean meal effectively mitigated the non-specific adsorption of lignosulfonate, resulting in a reduction of the surface area of lignin from 235.0 to 139.2 m2/g. The utilization of soybean meal as a cost-effective and efficient shielding agent significantly enhanced the efficiency of subsequent enzyme catalysis. Consequently, the application of soybean meal in commercial enzyme catalysis holds considerable appeal and amplifies the relevance of this study in preservative industries.

Developing nano-micro size chitosan beads using imidazolium-based ionic liquid: A perspective

The aggressive search for unique materials in recent years has put forward chitosan and modified-chitosan as materials with unique structural and morphological characteristics for various important applications. Just as imidazolium-based ionic liquids are the commonly applied ionic liquids (ILs) type for chitosan modifications for various applications, their further modifications into beads for enhancing their properties is now gaining most attention. However, most of the currently prepared imidazolium ILs modified-chitosan beads are not in nano size due to preparation difficulties. In response to this and referencing the research works in the literature, the possible breakthrough directions including synthesis routes, and physical and mechanical transformation processes are proposed. These procedures are expected to provide certain theoretical and empirical basis, as well as technical guide for developing nano-micro size chitosan beads using imidazolium based ILs.

Enzyme Immobilization Technologies and Industrial Applications

Enzymes play vital roles in diverse industrial sectors and are essential components of many industrial products. Immobilized enzymes possess higher resistance to environmental changes and can be recovered/recycled easily when compared to the free forms. The primary benefit of immobilization is protecting the enzymes from the harsh environmental conditions (e.g., elevated temperatures, extreme pH values, etc.). The immobilized enzymes can be utilized in various large-scale industries, e.g., medical, food, detergent, textile, and pharmaceutical industries, besides being used in water treatment plants. According to the required application, a suitable enzyme immobilization technique and suitable carrier materials are chosen. Enzyme immobilization techniques involve covalent binding, encapsulation, entrapment, adsorption, etc. This review mainly covers enzyme immobilization by various techniques and their usage in different industrial applications starting from 1992 until 2022. It also focuses on the multiscale operation of immobilized enzymes to maximize yields of certain products. Lastly, the severe consequence of the COVID-19 pandemic on global enzyme production is briefly discussed.

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.

Strategies towards Reduction of Cellulases Consumption: Debottlenecking the Economics of Lignocellulosics Valorization Processes

Lignocellulosic residues have been receiving growing interest as a promising source of polysaccharides, which can be converted into a variety of compounds, ranging from biofuels to bioplastics. Most of these can replace equivalent products traditionally originated from petroleum, hence representing an important environmental advantage. Lignocellulosic materials are theoretically unlimited, cheaper and may not compete with food crops. However, the conversion of these materials to simpler sugars usually requires cellulolytic enzymes. Being still associated with a high cost of production, cellulases are commonly considered as one of the main obstacles in the economic valorization of lignocellulosics. This work provides a brief overview of some of the most studied strategies that can allow an important reduction of cellulases consumption, hence improving the economy of lignocellulosics conversion. Cellulases recycling is initially discussed regarding the main processes to recover active enzymes and the most important factors that may affect enzyme recyclability. Similarly, the potential of enzyme immobilization is analyzed with a special focus on the contributions that some elements of the process can offer for prolonged times of operation and improved enzyme stability and robustness. Finally, the emergent concept of consolidated bioprocessing (CBP) is also described in the particular context of a potential reduction of cellulases consumption.

Stabilization of β-Galactosidase on Modified Gold Nanoparticles: A Preliminary Biochemical Study to Obtain Lactose-Free Dairy Products for Lactose-Intolerant Individuals

The unique chemical, optical, and electrical characteristics of nanoparticles make their utilization highly successful in every field of biological sciences as compared to their bulk counterpart. These properties arise as a result of their miniature size, which provides them an excellent surface area-to-volume ratio, inner structure, and shape, and hence increases their surface characteristics. Therefore, this study was undertaken to engineer gold nanoparticles (AuNPs) for improving their catalytic activity and stability in biotechnological processes. The characterization of AuNPs was performed by XRD, UV spectra, and TEM. The synthesized AuNPs were surface-modified by polyvinyl alcohol (PVA) for binding the enzyme in excellent yield. The developed immobilized enzyme system (PVA-AuNPs-β-galactosidase) displayed pH optima at pH 7.0 and temperature optima at 40 °C. Moreover, the stability of PVA-AuNPs-β-galactosidase was significantly enhanced at wider pH and temperature ranges and at higher galactose concentrations, in contrast to the free enzyme. β-galactosidase bound to PVA-modified AuNPs exhibited greater operational activity, even after its sixth reuse. The developed nanosystem may prove useful in producing lactose-free dairy products for lactose-intolerant patients.

Tunable Polymeric Scaffolds for Enzyme Immobilization

The number of methodologies for the immobilization of enzymes using polymeric supports is continuously growing due to the developments in the fields of biotechnology, polymer chemistry, and nanotechnology in the last years. Despite being excellent catalysts, enzymes are very sensitive molecules and can undergo denaturation beyond their natural environment. For overcoming this issue, polymer chemistry offers a wealth of opportunities for the successful combination of enzymes with versatile natural or synthetic polymers. The fabrication of functional, stable, and robust biocatalytic hybrid materials (nanoparticles, capsules, hydrogels, or films) has been proven advantageous for several applications such as biomedicine, organic synthesis, biosensing, and bioremediation. In this review, supported with recent examples of enzyme-protein hybrids, we provide an overview of the methods used to combine both macromolecules, as well as the future directions and the main challenges that are currently being tackled in this field.

Industrial attributes of β-glucanase produced by Bacillus sp. CSB55 and its potential application as bio-industrial catalyst

The β-glucanase produced from Bacillus sp. CSB55 not only depicts the potent industrial characteristics but also relates as bio-industrial catalyst supporting the spontaneous formation of the products, high hydrolytic efficiency, and feasibility of the enzymatic reaction. A homogeneous β-glucanase (GluB55) was purified via various purification processes resulting in 11.69% yield and 14.24-fold purity. Biochemical characterization of the purified enzyme revealed the molecular mass of approximately 40 kDa, which was verified by zymography. The optimum activity of GluB55 was determined at pH 7.2 and 55 °C. GluB55 could highly hydrolyze carboxymethylcellulose and was stable over a wide range of pH, retaining more than 70% residual activity at pH 5.8-11.0 and carried 100% thermostability as high as 60 °C. In addition, it showed 68% residual activity at 70 °C. The N-terminal amino acid sequence of GluB55 was Ala-Asn-Pro-Glu-Leu-Val-Asn-X-Gln-Ala-X-X-Ala-X-Gln-Gly. The enzyme activity was stimulated by Co²⁺ (158.6%), Zn²⁺ (211.1%), Mn²⁺ (264.4%), and Ba²⁺ (211.4%). Enzyme kinetics showed K_m and V_max values of 0.022 mg mL^-1 and 994.56 ± 3.72 U mg^-1, respectively. Q₁₀ was calculated to be 1.12. ∆H, ∆G, and ∆S were low revealing that the formation of the transition phase and conversion to the product is very well organized. The lower the free energy change (∆G), the more feasible is the reaction.

Optimization of aqueous enzymatic method for Camellia sinensis oil extraction and reuse of enzymes in the process

Aqueous enzymatic extraction of Camellia sinensis oil was studied. The results suggested that saponin removal pretreatment assisted by ultrasound was effective in decreasing emulsification and in enhancing the free oil recovery. After 70% isopropanol extraction for 30 min under ultrasound, the residue of C. sinensis seeds was further hydrolyzed with free cellulase and Alcalase for 5 h, and calcium ions were concurrently added during enzymatic hydrolysis (n_Ca²⁺: n_saponin = 1:2), and free oil recovery up to 94.14% was obtained. Separate immobilization and co-immobilization of Alcalase and cellulase were performed by alginate entrapment combined with glutaraldehyde crosslinking. Specific activity and recovery of activity for Alcalase and cellulase were acceptable. After immobilization, Alcalase and cellulase exhibited higher activity at a wider pH and temperature range. Reuse experiments of immobilized enzymes were conducted. The deactivation kinetics immobilized enzymes were simulated and half-life of immobilized enzyme was estimated. The results indicated that a magnetic supporter facilitated the recovery of immobilized enzymes from tea seed slurry, and that immobilized Alcalase and cellulase had good reusability.

Fungal Diversity and Enzyme Activity Associated with the Macroalgae, Agarum clathratum

Agarum clathratum, a brown macroalgae species, has recently become a serious environmental problem on the coasts of Korea. In an effort to solve this problem, fungal diversity associated with decaying A. clathratum was investigated and related β-glucosidase and endoglucanase activities were described. A total of 233 fungal strains were isolated from A. clathratum at 15 sites and identified 89 species based on morphology and a multigene analysis using the internal transcribed spacer region (ITS) and protein-coding genes including actin (act), β-tubulin (benA), calmodulin (CaM), and translation elongation factor (tef1). Acremonium, Corollospora, and Penicillium were the dominant genera, and Acremonium fuci and Corollospora gracilis were the dominant species. Fifty-one species exhibited cellulase activity, with A. fuci, Alfaria terrestris, Hypoxylon perforatum, P. madriti, and Pleosporales sp. Five showing the highest enzyme activities. Further enzyme quantification confirmed that these species had higher cellulase activity than P. crysogenum, a fungal species described in previous studies. This study lays the groundwork for bioremediation using fungi to remove decaying seaweed from populated areas and provides important background for potential industrial applications of environmentally friendly processes.

Immobilization of cellulase in the non-natural ionic liquid environments to enhance cellulase activity and functional stability

Ionic liquids (ILs) have been applied as an environmentally friendly solvent in the pretreatment of lignocellulosic biomass for more than a decade. The ILs involved pretreatment processes for cellulases mediated saccharification lead to both the breakdown of cellulose crystallinity and the decrease of lignin content, thereby improving the solubility of cellulose and the accessibility of cellulase. However, most cellulases are partially or completely inactivated in the presence of even low amount of ILs. Immobilized cellulases are found to perform improved stability and higher apparent activity in practical application compared with its free counterparts. Enzyme immobilization therefore has become a promising way to relieve the deactivation of cellulase in ILs. Various immobilization carriers and methods have been developed and achieved satisfactory results in improving the stability, activity, and recycling of cellulases in IL pretreatment systems. This review aims to provide detailed introduction of immobilization methods and carrier materials of cellulase, including natural polysaccharides, synthetic polymers, inorganic materials, magnetic materials, and newly developed composite materials, and illustrate key methodologies in improving the performance of cellulase in the presence of ILs. Especially, novel materials and concepts from the recently representative researches are focused and discussed comprehensively, and future trends in immobilization of cellulases in non-natural ILs environments are speculated in the end.

Efficient Physisorption of Candida Antarctica Lipase B on Polypropylene Beads and Application for Polyester Synthesis

In the present work, Candida antarctica lipase B (CaLB) was adsorbed onto polypropylene beads using different reaction conditions, in order to investigate their influence on the immobilization process and the enzyme activity of the preparations in polymerization reactions. In general, lower salt concentrations were more favorable for the binding of enzyme to the carrier. Polymerisation of dimethyl adipate (DMA) and 1,4-butanediol (BDO) was investigated in thin-film systems at 70 °C and at both atmosphere pressure (1000 mbar) and 70 mbar. Conversion rates and molecular masses of the reaction products were compared with reactions catalyzed by CaLB in its commercially available form, known as Novozym 435 (CaLB immobilized on macroporous acrylic resin). The best results according to molecular weight and monomer conversion after 24 h reaction time were obtained with CaLB immobilized in 0.1 M Na2HPO4\NaH2PO4 buffer at pH 8, producing polyesters with 4 kDa at conversion rates of 96% under low pressure conditions. The stability of this preparation was studied in a simulated continuous polymerization process at 70 °C, 70 mbar for 4 h reaction time. The data of this continuous polymerizations show that the preparation produces lower molecular weights at lower conversion rates, but is comparable to the commercial enzyme concerning stability for 10 cycles. However, after 24 h reaction time, using our optimum preparation, higher molecular weight polyesters (4 kDa versus 3.1 kDa) were obtained when compared to Novozym 435.

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

In present study, Aspergillus niger cellulase was immobilized onto functionalized multiwalled carbon nanotubes (MWCNTs) via carbodiimide coupling. MWCNTs offer unique advantages including enhanced electronics properties, a large edge to basal plane ratio, rapid electrode kinetics and it's possess higher tensile strength properties due to their structural arrangements. The immobilization was confirmed by FTIR (Fourier transform infrared spectroscopy) and SEM (scanning electron microscope). The bionanoconjugates prepared under optimized condition retained 85% activity with improved pH and thermal stability. The t_1/2 of immobilized cellulase at 70 °C was four fold higher than free enzyme. The Km value indicates that affinity of bionanoconjugates towards substrate has increased by two times. The preparation could be reused ten times without much loss in enzyme activity. The enhanced catalytic efficiency, stability and reusability makes it useful for efficient cellulose hydrolysis.

FoldX as Protein Engineering Tool: Better Than Random Based Approaches?

Improving protein stability is an important goal for basic research as well as for clinical and industrial applications but no commonly accepted and widely used strategy for efficient engineering is known. Beside random approaches like error prone PCR or physical techniques to stabilize proteins, e.g. by immobilization, in silico approaches are gaining more attention to apply target-oriented mutagenesis. In this review different algorithms for the prediction of beneficial mutation sites to enhance protein stability are summarized and the advantages and disadvantages of FoldX are highlighted. The question whether the prediction of mutation sites by the algorithm FoldX is more accurate than random based approaches is addressed.

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.

Utilization of spent coffee grounds for isolation and stabilization of Paenibacillus chitinolyticus CKS1 cellulase by immobilization

This study has explored the feasibility of using spent coffee grounds as a good supporting material for the Paenibacillus chitinolyticus CKS1 cellulase immobilization. An optimal operational conditions in a batch-adsorption system were found to be: carrier mass of 12 g/L, under the temperature of 45 °C and no pH adjustments. The immobilization yield reached about 71%. An equilibrium establishment between the cellulase and the carrier surface occurred within 45 min, whereas the process kinetics may be predicted by the pseudo-second-order model. An immobilized cellulase preparation expressed very good avicelase activity, this reached up to 2.67 U/g, and revealed an improved storage stability property, compared to free enzyme sample counterpart. The addition of metal ions, such as K⁺ and Mg²⁺ did not affect positively immobilization yield results, but on the contrary, contributed to an improved bio-activities of the immobilized cellulase, thus may be employed before each enzyme application. The method developed in this study offers a cheap and effective alternative for immediate enzyme isolation from the production medium and its stabilization, compared to other carriers used for the immobilization.

Purification and Immobilization of a Novel Enantioselective Lipase from Tsukamurella tyrosinosolvents for Efficient Resolution of Ethyl 2-(2-oxopyrrolidin-1-yl) Butyrate

A highly enantioselective lipase from Tsukamurella tyrosinosolvents E105 was purified via ultrasonic extraction, precipitation, and chromatographic steps. The enzyme was purified about 38-fold with the recovery yield of 9 % and was confirmed as a dimer protein consisting of two identical subunits with a molecular mass of 24 kDa. The purified lipase was used to catalyze resolution of racemic ethyl 2-(2-oxopyrrolidin-1-yl) butyrate to (S)-2-(2-oxopyrrolidin-1-yl) butyric acid. The maximum activity of such lipase was obtained at pH 7.5, 35 °C, and the highest relative activity (156.80 %) was observed in the presence of 0.5 mM Co²⁺. Subsequently, the lipase was encapsulated within a mixture of 3 % sodium alginate and 0.8 % carrageenan, and then cross-linked with 0.6 % glutaraldehyde to enhance its biocatalytic capability and stability. Comparing with 36.9 % product yield and 97.5 % product ee of free lipase, the highest product yield of 46.3 % and ee of 98.5 % for immobilized lipase were achieved with the presence of 20 mM substrate. In addition, the reusability of immobilized lipase was also investigated, which could maintain 63.7 % of its initial conversion yield after seven repeated batch reactions. Thus, the evaluated enantioselective lipase in this work has a good potential for further industrial application.

Immobilization of ω-transaminase by magnetic PVA-Fe3O4 nanoparticles

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Core–shell composite Fe₃O₄-PVA was prepared successfully by chemical co-precipitation, and it has a good characterization results.

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Fe₃O₄-PVA was firstly and successfully used to immobilize ω-TA.

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ω-TA which immobilized onto Fe₃O₄-PVA could be successfully separated and reused for many times in biotransformation with its activity no declined.

ω-Transaminase (ω-TA) as a kind of important biocatalyst is widely used in preparation of chiral intermediates. In this paper, a magnetic PVA-Fe₃O₄ nanoparticles was prepared and employed on immobilization of ω-TA to reduce the cost, increase reusability and enhance stability. The prepared magnetic PVA-Fe₃O₄ nanoparticles were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The average size of magnetic PVA-Fe₃O₄ nanoparticles was located between 30–40 nm ω-TA was immobilized onto magnetic PVA-Fe₃O₄ nanoparticles via glutaraldehyde cross-linking, achieving a wider pH range as 6–8 and also a better thermal stability at 60 °C. Meanwhile, the immobilized ω-TA could be successfully reused for 13 times in biotransformation. These results therefore indicated that the immobilized ω-TA with high stability might be readily utilized in industrial purposes.

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.

Immobilization of catalase on electrospun PVA/PA6-Cu(II) nanofibrous membrane for the development of efficient and reusable enzyme membrane reactor

In this study, a mat/membrane consisting of overlaid PVA/PA6-Cu(II) composite nanofibers was prepared via the electrospinning technique followed by coordination/chelation with Cu(II) ions; an enzyme of catalase (CAT) was then immobilized onto the PVA/PA6-Cu(II) nanofibrous membrane. The amount of immobilized catalase reached a high value of 64 ± 4.6 mg/g, while the kinetic parameters (Vmax and Km) of enzyme were 3774 μmol/mg·min and 41.13 mM, respectively. Furthermore, the thermal stability and storage stability of immobilized catalase were improved significantly. Thereafter, a plug-flow type of immobilized enzyme membrane reactor (IEMR) was assembled from the PVA/PA6-Cu(II)-CAT membrane. With the increase of operational pressure from 0.02 to 0.2 MPa, the flux value of IEMR increased from 0.20 ± 0.02 to 0.76 ± 0.04 L/m(2)·min, whereas the conversion ratio of H2O2 decreased slightly from 92 ± 2.5% to 87 ± 2.1%. After 5 repeating cycles, the production capacity of IEMR was merely decreased from 0.144 ± 0.006 to 0.102 ± 0.004 mol/m(2)·min. These results indicated that the assembled IEMR possessed high productivity and excellent reusability, suggesting that the IEMR based on electrospun PVA/PA6-Cu(II) nanofibrous membrane might have great potential for various applications, particularly those related to environmental protection.

Separation of lignocresol from eucalyptus lignocresol-cellulase complex using organic solvents

A functional lignin-based material, lignocresol, was synthesized from eucalyptus wood meal by using phase separation treatment with p-cresol and 72% sulfuric acid. Lignocresol physically adsorbs Trichoderma reesei cellulase and functions as an immobilized cellulase. Lignocresol-immobilized cellulase was treated with acetone or ethanol to separate the enzyme and its support. Most lignocresol was dissolved in organic solvents and then precipitated in diethyl ether. The recovery yield of lignocresol using acetone was 85% and that using ethanol was 72%, with very low or negligible residual cellulase. Lignocresol is an innovative recyclable enzyme support that can be easily separated using only organic solvents after deactivation of the immobilized enzyme.