Preparation and use of cross-linked enzyme aggregates (CLEAs) of laccases

Cross-linked enzyme aggregates of polyethylene terephthalate hydrolyse (PETase) from Ideonella sakaiensis for the improvement of plastic degradation

Polyethylene terephthalate (PET) is one of the most produced plastics globally and its accumulation in the environment causes harm to the ecosystem. Polyethylene terephthalate hydrolyse (PETase) is an enzyme that can degrade PET into its monomers. However, free PETase lacks operational stabilities and is not reusable. In this study, development of cross-linked enzyme aggregate (CLEA) of PETase using amylopectin (Amy) as cross-linker was introduced to solve the limitations of free PETase. PETase-Amy-CLEA exhibited activity recovery of 81.9 % at its best immobilization condition. Furthermore, PETase-Amy-CLEA exhibited 1.37-, 2.75-, 2.28- and 1.36-fold higher half-lives than free PETase at 50 °C, 45 °C, 40 °C and 35 °C respectively. Moreover, PETase-Amy-CLEA showed broader pH stability from pH 5 to 10 and could be reused up to 5 cycles. PETase-Amy-CLEA retained >70 % of initial activity after 40 days of storage at 4 °C. In addition, lower Km of PETase-Amy-CLEA indicated better substrate affinity than free enzyme. PETase-Amy-CLEA corroded PET better and products yielded was 66.7 % higher than free PETase after 32 h of treatment. Hence, the enhanced operational stabilities, storage stability, reusability and plastic degradation ability are believed to make PETase-Amy-CLEA a promising biocatalyst in plastic degradation.

Enzymes in "Green" Synthetic Chemistry: Laccase and Lipase

Enzymes play an important role in numerous natural processes and are increasingly being utilized as environmentally friendly substitutes and alternatives to many common catalysts. Their essential advantages are high catalytic efficiency, substrate specificity, minimal formation of byproducts, and low energy demand. All of these benefits make enzymes highly desirable targets of academic research and industrial development. This review has the modest aim of briefly overviewing the classification, mechanism of action, basic kinetics and reaction condition effects that are common across all six enzyme classes. Special attention is devoted to immobilization strategies as the main tools to improve the resistance to environmental stress factors (temperature, pH and solvents) and prolong the catalytic lifecycle of these biocatalysts. The advantages and drawbacks of methods such as macromolecular crosslinking, solid scaffold carriers, entrapment, and surface modification (covalent and physical) are discussed and illustrated using numerous examples. Among the hundreds and possibly thousands of known and recently discovered enzymes, hydrolases and oxidoreductases are distinguished by their relative availability, stability, and wide use in synthetic applications, which include pharmaceutics, food and beverage treatments, environmental clean-up, and polymerizations. Two representatives of those groups-laccase (an oxidoreductase) and lipase (a hydrolase)-are discussed at length, including their structure, catalytic mechanism, and diverse usage. Objective representation of the current status and emerging trends are provided in the main conclusions.

Detoxification and decolorization of complex textile effluent in an enzyme membrane reactor: batch and continuous studies

There is an urgent need to look for bio-based technologies to address the pollution related to textile dyes in waterbodies. The aim of this study was to evaluate an engineered laccase variant, LCC1-62 of Cyathus bulleri, expressed in recombinant Pichia pastoris, for the decolorization and detoxification of real textile effluent. The partially purified laccase effectively (~60-100%) decolorized combined effluent from different dyeing units at a laccase concentration of 500 U/L at a 50-mL level. Decolorization and detoxification of the combined effluents, from a local textile mill, were evaluated at 0.3 L volumetric level in a ray-flow membrane reactor in batch and continuous modes of operation. In batch studies, maximum decolorization of 97% and detoxification of 96% occurred at a hydraulic retention time (HRT) of 6 h without any additional laccase requirement. In continuous studies, the reactor was operated at an HRT of 6 h with a lower enzyme dosage (~120 U/L of the effluent). Decolorization was accompanied by a loss in laccase activity which was restored to ~120 U/L by the addition of laccase in two regimes. The addition of laccase, when the residual laccase activity decreased to 40% (~50 U/L), resulted in high decolorization (~5 ppm residual dye concentration) and low variance (σ²) of 2.77, while laccase addition, when the residual dye concentration decreased to ~8% (~10 U/L), resulted in an average dye concentration of 13 ppm with a high variance of 62.08. The first regime was implemented, and the continuous reactor was operated for over 80 h at an HRT of 3 and 6 h, with the latter resulting in ~95% decolorization and 96% reduction in the mutagenicity of the effluent. Less than 10% membrane fouling was observed over long operations of the reactor. The findings strongly suggest the feasibility of using LCC1-62 in an enzyme membrane reactor for large-scale treatment of textile effluents.

Functionalized chitosan and sodium alginate for the effective removal of recalcitrant organic pollutants

In this work, the study of an oxidative-coupling reaction by immobilization of laccase or horseradish peroxidase (HRP) onto chitosan and sodium alginate was reported. The oxidative-coupling reaction of three recalcitrant organic pollutants (ROPs) such as chlorophenol compounds including 2,4-dichlorophenol (DCP), 2,4,6- trichlorophenol (TCP), pentachlorophenol (PCP) was studied. The results showed that the systems with immobilized laccase or horseradish peroxidase had broader range of optimum pH and temperature when compared to that of free laccase and horseradish peroxidase. The removal efficiencies of DCP, TCP and PCP within 6 h were found to be 77 %, 90 % and 83 %, respectively. The rate constants of the first order reactions for laccase were arranged as 0.30 h^-1 (TCP) > 0.13 h^-1 (DCP) > 0.11 h^-1 (PCP) and the rate constants for HRP were arranged as 0.42 h^-1 (TCP) > 0.32 h^-1 (PCP) > 0.25 h^-1 (DCP). The removal rate of TCP was found to be the highest among all and the removal efficiency of ROPs by HRP was always better than that of laccase. The major products of the reaction were identified by LC-MS and confirmed as humic-like polymers.

Removal of pentachlorophenol and phenanthrene from lignocellulosic biorefinery wastewater by a biocatalytic/biosurfactant system comprising cross-linked laccase aggregates and rhamnolipid

Synthesis and characterization of highly active cross-linked laccase aggregates (CLLAs) were performed and evaluated for removal of pentachlorophenol and phenanthrene from lignocellulosic biorefinery wastewater. Laccase from Tramates versicolor MTCC 138 was insolubilized as CLLAs via precipitation with 70% ammonium sulphate and simultaneous cross-linking with 5 mM glutaraldehyde to obtain activity recovery of 89.1%. Compared to the free laccase, the pH and thermal stability of the prepared CLLAs were significantly higher. At a high temperature of 60 °C, free laccase had a half-life of 0.25 h, while CLLAs had a half-life of 6.2 h. In biorefinery wastewater (pH 7.0), the free and CLLAs were stored for 3 day at a temperature of 30 °C. Free laccase completely lost their initial activity after 60 h; however, the CLLAs retained 39% activity till 72 h. Due to its excellent stability, free laccase and CLLAs were assessed for removing pentachlorophenol and phenanthrene in wastewater. CLLAs could remove 51-58% of pentachlorophenol (PCP) and phenanthrene (PHE) in 24 h. Biosurfactants, including surfactin, sophorolipid, and rhamnolipid, were assessed for their aptitude to improve the removal of organic contaminants in wastewater. Biorefinery wastewater incubated with all surfactants enhanced PCP and PHE removal compared to the no-surfactant controls. Further, 1 μM rhamnolipid significantly amplified pentachlorophenol and phenanthrene removal to 81-93% for free laccase and CLLAs, respectively.

Applications and immobilization strategies of the copper-centred laccase enzyme; a review

Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.

Bio-imprinted magnetic cross-linked polyphenol oxidase aggregates for enhanced synthesis of L-dopa, a neurodegenerative therapeutic drug

Bio-imprinted magnetic cross-linked enzyme aggregates (i-m-CLEAs) of polyphenol oxidase (PPO) obtained from potato peels were prepared using amino-functionalized magnetic nanoparticles. Bio-imprinting is being used to improve the catalytic efficiency and conformational stability of enzymes. For bio-imprinting, PPO was incubated with different imprint/template molecules (catechol, 4-methyl catechol and l-3,4-dihydroxy phenylalanine) before cross-linking with glutaraldehyde. CLEAs imprinted with 4-methyl catechol showed maximum activity as compared with non-bio-imprinted magnetic CLEAs (m-CLEAs). They were further characterized by scanning electron microscopy and confocal microscopy. In bio-imprinted m-CLEAs, half-life (t_1/2) of PPO significantly improved (364.74 min) as compared to free PPO (43.58 min) and non-bio-imprinted m-CLEAs (266.54 min). Bio-imprinted m-CLEAs showed excellent thermal and storage stability as well as reusability. The CLEAs preparation were used for the synthesis of l-3,4-dihydroxyphenylalanine (L-dopa, a therapeutic drug to treat neurodegenerative disorder) and a remarkable increase in L-dopa yield (23.5-fold) was obtained as compared to free enzyme. A cost effective and reusable method has been described for the production of L-dopa.

Feasibility and potential of laccase-based enzyme in wastewater treatment through sustainable approach: A review

The worldwide increase in metropolitan cities and rise in industrialization have resulted in the assimilation of hazardous pollutants into the ecosystems. Different physical, chemical and biological techniques have been employed to remove these toxins from water bodies. Several bioprocess applications using microbes and their enzymes are utilized to achieve the goal. Biocatalysts, such as laccases, are employed explicitly to deplete a variety of organic pollutants. However, the degradation of contaminants using biocatalysts has many disadvantages concerning the stability and activity of the enzyme. Hence, they are immobilized on different supports to improve the enzyme kinetics and recyclability. Furthermore, standard wastewater treatment methods are not effective in eliminating all the contaminants. As a result, membrane separation technologies have emerged to overcome the limitations of traditional wastewater treatment methods. Moreover, enzymes immobilized onto these membranes have generated new avenues in wastewater purification technology. This review provides the latest information on laccases from diverse sources, their molecular framework and their mode of action. This report also gives information about various immobilization techniques and the application of membrane bioreactors to eliminate and biotransform hazardous contaminants. In a nutshell, laccases appear to be the most promising biocatalysts for green and cost-efficient wastewater treatment technologies.

Laccase-assisted degradation of emerging recalcitrant compounds - A review

The main objective of this review is to provide up to date, brief, irrefutable, organized data on the conducted experiments on a range of emerging recalcitrant compounds such as Diclofenac (DCF), Chlorophenols (CPs), tetracycline (TCs), Triclosan (TCS), Bisphenol A (BPA) and Carbamazepine (CBZ). These compounds were selected from the categories of pharmaceutical contaminants (PCs), endocrine disruptors (EDs) and personal care products (PCPs) on the basis of their toxicity and concentration retained in the environment. In this context, detailed mechanism of laccase mediated degradation has been conversed that laccase assisted degradation occurs by one electron oxidation involving redox potential as underlying element of the process. Further, converging towards biotechnology, laccase immobilization increased removal efficiency, storage and reusability through various experimentally conducted studies. Laccase is being considered noteworthy as mediators facilitate laccase in oxidation of non-phenolic compounds and thereby increasing its substrate range which is being discussed in further in the review. The laccase assisted degradation mechanism of each compound has been elucidated but further studies to undercover proper degradation mechanisms needs to be performed.

Nanomaterial-based electrochemical enzymatic biosensors for recognizing phenolic compounds in aqueous effluents

With the rapid development of industrial society, phenolic pollutants already identified in water are severe threats to human health. Traditional detection techniques like chromatography are poor in the ability of cost-effectiveness and on-site detection. In recent years, electrochemical enzymatic biosensors have attracted increasing attention for use in the recognition of phenolic compounds, which is considered an effective strategy for the product transfer of portable analytical devices. Although electrochemical enzymatic biosensors provide a fast, accurate on-site detection technique, the difficulties of enzyme deactivation, poor stability and low sensitivity remain to be solved. Thus, effective immobilization methods of enzymes and nanomaterials with excellent properties have been extensively researched to obtain a high-sensitivity and high-stability biosensing platform. Simultaneous detection of multiple phenols may become the focus of further research. In this review, we provide an overview of recent progress toward electrochemical enzymatic biosensors for the detection of phenolic compounds, including enzyme immobilization approaches and advanced nanomaterials, especially nanocomposites with attractive properties such as good conductivity, high specific surface area, and porous structure. We will comprehensively discuss the features and mechanisms of the main enzymes adopted in the construction of different phenolic biosensors, as well as traditional methods (e.g., adsorption, covalent bonding, entrapment, encapsulation, cross-linking) of enzyme immobilization. The most effective method is based on the properties of enzymes, supports and application objective because there is no one-size-fits-all method of enzymatic immobilization. The emphasis will be given to various advanced nanomaterials, including their special nanostructures, preparation methods and performance. Finally, the main challenges in future research on electrochemical phenolic biosensors will be discussed to provide further perspectives for practical applications in dynamic and on-site monitoring. We believe this review will deliver an important inspiration for the construction of novel and high-performance electrochemical biosensors from enzyme selection to nanomaterial design for the detection of various hazardous materials. We believe this review will deliver an important inspiration on the construction of novel and high-performance electrochemical biosensors from the enzyme selection to the nanomaterial design for detections of various hazardous materials.

Laccase Cross-Linked Ultraporous Aluminas for Sustainable Biodegradation of Remazol Brilliant Blue R

Over the past few decades, enzyme-based green and sustainable chemistry has attracted extensive research attention, which provides a promising alternative to the conventional treatment methods of recalcitrant micropollutants. However, enzyme denaturation and stability loss remain critical challenges for its potential applications in industrial wastewater treatment. In this study, laccase from Trametes versicolor (laccase T.) was cross-linked immobilized by ultraporous alumina (UPA) for the sustainable biodegradation of Remazol Brilliant Blue R (RBBR). Through sequential use of an aminosilane coupling agent (3-aminopropyl)triethoxysilane (APTES) and bifunctional cross-linker glutaraldehyde (GA), the synthesized biocatalysts showed better immobilization performances (about 4-fold to physical adsorption). The GA concentration considerably affected the laccase T. cross-linking degree, while the GA post-treatment protocol showed the highest laccase T. immobilization yield with lower activity recovery. Moreover, the biocatalyst stabilities including pH stability, thermal stability, storage stability, and reusability were also studied. Tolerance to broader pH and temperature ranges, better storage stability, good reusability of laccase T. cross-linked UPA(γ) biocatalysts, and their continuous RBRR biodegradation efficiency highlight the potentials of enzyme-based inorganic materials in industrial wastewater treatment, which can broaden our understanding of their practical applications in environmental fields.

Insolubilization of Tramates versicolor laccase as cross-linked enzyme aggregates for the remediation of trace organic contaminants from municipal wastewater

The novelty of this study deals with the biocatalytic treatment of trace organic contaminants (TrOCs) from municipal wastewater by insolubilized laccase. Laccase from Trametes versicolor was aggregated by three-phase partitioning technique followed by cross-linking with glutaraldehyde to produce insolubilized laccase as cross-linked enzyme aggregates (CLEAs). The optimal conditions for CLEAs preparation include ammonium sulphate concentration of 83% (w/v), crude to t-butanol ratio of 1.00: 1.05 (v/v), pH 5.3, and glutaraldehyde concentration of 20 mM obtained via statistical design. The efficiency of insolubilization of the CLEAs laccase based on the k_cat/k_m ratio was approximately 4.8-fold greater than that of free laccase. The developed CLEAs showed greater resistance to product inhibition mediated by ABTS than the free enzyme and exhibited excellent catalytic activity even after the tenth successive cycle. Further, free laccase and the synthesized CLEAs laccase were utilized to treat five analgesics, two NSAIDS, three antibiotics, two antilipemics, and three pesticides in the municipal wastewater. Under the batch process with operating conditions of pH 7.0 and 20 °C, 1000 U/L of CLEAs, laccase removed 11 TrOCs in the range of about 20-99%. However, the inactivated CLEAs only adsorbed 2-25% of TrOCs. It was observed that acetaminophen, mefenamic acid, trimethoprim, and metolachlor depicted almost complete removal with CLEAs laccase. The performance of CLEAs laccase in a perfusion basket reactor was tested for the removal of TrOCs from municipal wastewater.

Zinc oxide nanoparticles-impregnated chitosan surfaces for covalent immobilization of trypsin: Stability & kinetic studies

Trypsin (Try, EC. 3.4.21.4) was effectively immobilized on the surface of glutaraldehyde(GA)-activated ZnO/Chitosan nanocomposite through covalent attachment via Schiff-base linkages. Size, structure, surface morphology, & percentage elemental composition of the prepared ZnO nanoparticles and chitosan-coated ZnO nanocomposite were studied by UV-Visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-Ray diffraction analysis (XRD), transmission electron microscopy (TEM), Scanning electron microscopy (SEM), and Energy-Dispersive X-Ray Microanalysis (EDAX) techniques. Optimal immobilization conditions (incubation time (16 h), enzyme concentration (1.8 mg/ml), and pH (7.8)) were investigated to obtain the maximum expressed activity of the immobilized trypsin. Immobilized & solubilized trypsin exhibited the optimum catalytic activity at pH 8.5, 60 °C, and pH 7.8, 45 °C respectively. Kinetic parameters (K_m, V_max) of immobilized (27.12 μM, 8.82 μM/min) & free trypsin (25.76 μM, 4.16 μM/min) were determined, indicating that efficiency of trypsin improves after immobilization. Immobilized trypsin preserved 67% of initial activity at 50 °C during 2 h of incubation & sustained nearly 50% of catalytic activity until the 9th repeated cycle of utilization. Moreover, immobilized trypsin retained 50% of enzymatic activity after 90 days of storage at 4 °C. Hence, the current findings suggest that ZnO/Chitosan-GA-Trypsin would be a promising biocatalyst for large-scale biotechnological applications.

An Insight in Developing Carrier-Free Immobilized Enzymes

Enzymes play vital roles in all organisms. The enzymatic process is progressively at its peak, mainly for producing biochemical products with a higher value. The immobilization of enzymes can sometimes tremendously improve the outcome of biocatalytic processes, making the product(s) relatively pure and economical. Carrier-free immobilized enzymes can increase the yield of the product and the stability of the enzyme in biocatalysis. Immobilized enzymes are easier to purify. Due to these varied advantages, researchers are tempted to explore carrier-free methods used for the immobilization of enzymes. In this review article, we have discussed various aspects of enzyme immobilization, approaches followed to design a process used for immobilization of an enzyme and the advantages and disadvantages of various common processes used for enzyme immobilization.

Recent Developments in the Immobilization of Laccase on Carbonaceous Supports for Environmental Applications - A Critical Review

Τhe ligninolytic enzyme laccase has proved its potential for environmental applications. However, there is no documented industrial application of free laccase due to low stability, poor reusability, and high costs. Immobilization has been considered as a powerful technique to enhance laccase's industrial potential. In this technology, appropriate support selection for laccase immobilization is a crucial step since the support could broadly affect the properties of the resulting catalyst system. Through the last decades, a large variety of inorganic, organic, and composite materials have been used in laccase immobilization. Among them, carbon-based materials have been explored as a support candidate for immobilization, due to their properties such as high porosity, high surface area, the existence of functional groups, and their highly aromatic structure. Carbon-based materials have also been used in culture media as supports, sources of nutrients, and inducers, for laccase production. This study aims to review the recent trends in laccase production, immobilization techniques, and essential support properties for enzyme immobilization. More specifically, this review analyzes and presents the significant benefits of carbon-based materials for their key role in laccase production and immobilization.

Enhancing stability and by-product tolerance of β-glucuronidase based on magnetic cross-linked enzyme aggregates

β-glucuronidase is an important catalyst which is highly specific for β-glucuronides. Here, we constructed magnetic cross-linking β-glucuronidase aggregates (MCLEAs) to for the production of glycyrrhetinic acid (GA). Before crosslinking via glutaraldehyde, we used carbodiimide to enhance the interaction between enzymes and carboxyl-functionalized Fe₃O₄, efficiently improving the activity recovery. Compared to free enzymes, both k_cat and k_cat/K_m enhanced, indicating that crosslinking and aggregation brought higher catalytic efficiency to enzymes. MCLEAs enhanced pH and thermal stabilities and retained 63.3% of catalytic activity after 6 cycles. More importantly, it was first found that the glucuronic acid tolerance of β-glucuronidase after the formation of MCLEAs enhanced 221.5% in 10 mM of glucuronic acid. According to the Raman spectroscopy, the ordered structure of β-glucuronidase increased from 43.9% to 50.6% after immobilization, which explained the increased stability and tolerance. To sum up, MCLEAs provided an efficient strategy for immobilization of enzymes, which enhanced stability and glucuronic acid tolerance of enzymes. It might be an effective solution to the serious inhibition caused by by-products during the preparation of aglycone from natural glycosides, having a significant applied prospect in industry.

A review: Evolution of enzymatic biofuel cells

Ever-growing demands for energy, the unsustainability of fossil fuel due to its scarcity and massive impact on global economies and the environment, have encouraged the research on alternative power sources to work upon for the governments, companies, and scientists across the world. Enzymatic biofuel cells (eBFCs) is one category of fuel cell that can harvest energy from biological moieties and has the future to be used as an alternative source of energy. The aim of this review is to summarize the background and state-of-the-art in the field of eBFCs. This review article will be very beneficial for a wide audience including students and new researchers in the field. A part of the paper summarized the challenges in the preparation of anode and cathode and the involvement of nanomaterials and conducting polymers to construct the effective bioelectrodes. It will provide an insight for the researchers working in this challenging field. Furthermore, various applications of eBFCs in implantable power devices, tiny electronic gadgets, and self powered biosensors are reported. This review article explains the development in the area of eBFCs for several years from its origin to growth systematically. It reveals the strategies that have been taken for the improvements required for the better electrochemical performance and operational stability of eBFCs. It also mentions the challenges in this field that will require proper attention so that the eBFCs can be utilized commercially in the future. The review article is written and structurized in a way so that it can provide a decent background of eBFCs to its reader. It will definitely help in enhancing the interest of reader in eBFCs.

Laccase-mediated delignification and detoxification of lignocellulosic biomass: removing obstacles in energy generation

The rising global population and worldwide industrialization have led to unprecedented energy demand that is causing fast depletion of fossil reserves. This has led to search for alternative energy sources that are renewable and environment friendly. Use of lignocellulosic biomass for energy generation is considered a promising approach as it does not compete with food supply. However, the lignin component of the biomass acts as a natural barrier that prevents its efficient utilization. In order to remove the lignin and increase the amount of fermentable sugars, the lignocellulosic biomass is pretreated using physical and chemical methods which are costly and hazardous for environment. Moreover, during the traditional pretreatment process, numerous inhibitory compounds are generated that adversely affect the growth of fermentative microbes. Alternatively, biological methods that use microbes and their enzymes disrupt lignin polymers and increase the accessibility of the carbohydrates for the sugar generation. Microbial laccases have been considered as an efficient biocatalyst for delignification and detoxification offering a green initiative for energy generation process. The present review aims to bring together recent studies in bioenergy generation using laccase biocatalyst in the pretreatment processes. The work provides an overview of the sustainable and eco-friendly approach of biological delignification and detoxification through whole-cell and enzymatic methods, use of laccase-mediator system, and immobilized laccases for this purpose. It also summarizes the advantages, associated challenges, and potential prospects to overcome the limitations.

Current Status and Future Perspectives of Supports and Protocols for Enzyme Immobilization

The market for industrial enzymes has witnessed constant growth, which is currently around 7% a year, projected to reach $10.5 billion in 2024. Lipases are hydrolase enzymes naturally responsible for triglyceride hydrolysis. They are the most expansively used industrial biocatalysts, with wide application in a broad range of industries. However, these biocatalytic processes are usually limited by the low stability of the enzyme, the half-life time, and the processes required to solve these problems are complex and lack application feasibility at the industrial scale. Emerging technologies create new materials for enzyme carriers and sophisticate the well-known immobilization principles to produce more robust, eco-friendlier, and cheaper biocatalysts. Therefore, this review discusses the trending studies and industrial applications of the materials and protocols for lipase immobilization, analyzing their advantages and disadvantages. Finally, it summarizes the current challenges and potential alternatives for lipases at the industrial level.

Contemporary Techniques for Remediating Endocrine-Disrupting Compounds in Various Water Sources: Advances in Treatment Methods and Their Limitations

Over the years, the persistent occurrence of superfluous endocrine-disrupting compounds (EDCs) (sub µg L⁻¹) in water has led to serious health disorders in human and aquatic lives, as well as undermined the water quality. At present, there are no generally accepted regulatory discharge limits for the EDCs to avert their possible negative impacts. Moreover, the conventional treatment processes have reportedly failed to remove the persistent EDC pollutants, and this has led researchers to develop alternative treatment methods. Comprehensive information on the recent advances in the existing novel treatment processes and their peculiar limitations is still lacking. In this regard, the various treatment methods for the removal of EDCs are critically studied and reported in this paper. Initially, the occurrences of the EDCs and their attributed effects on humans, aquatic life, and wildlife are systematically reviewed, as well as the applied treatments. The most noticeable advances in the treatment methods include adsorption, catalytic degradation, ozonation, membrane separation, and advanced oxidation processes (AOP), as well as hybrid processes. The recent advances in the treatment technologies available for the elimination of EDCs from various water resources alongside with their associated drawbacks are discussed critically. Besides, the application of hybrid adsorption–membrane treatment using several novel nano-precursors is carefully reviewed. The operating factors influencing the EDCs’ remediations via adsorption is also briefly examined. Interestingly, research findings have indicated that some of the contemporary techniques could achieve more than 99% EDCs removal.

Enzyme polymer engineered structure strategy to enhance cross-linked enzyme aggregate stability: a step forward in laccase exploitation for cannabidiol removal from wastewater

Despite all its advantages and potential, cross-linking enzyme aggregate (CLEA) technology is still not applied at an industrial scale for enzyme insolubilization for bioremediation purposes. In this study, the enzyme polymer engineered structure (EPES) method was used to enhance CLEA stability and reuse. A crude laccase from Trametes hirsuta was successfully insolubilized to form EPES-CLEAs. The polymeric network provided excellent stability (> 90%) to CLEAs after a 24-h incubation in a non-buffered municipal wastewater effluent (WW), and the biocatalysts were recycled using a centrifugation process. While CLEAs activity dropped to 17%, EPES-CLEAs showed a laccase activity retention of 67% after five cycles of 2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) oxidation. After 8 h of treatment in WW, the EPES-CLEAs were equally as effective in removing cannabidiol (CBD) as the free-LAC (~ 37%). This research demonstrates that the EPES method is a promising alternative for CLEA stabilization and reuse in environmental conditions.

Carrier-Free Immobilization of α-Galactosidase as Nano-Biocatalysts for Synthesizing Prebiotic α-Galacto-Oligosaccharides

α-Galacto-oligosaccharides (α-GOSs) have great functions as prebiotics and therapeutics. This work established the method of batch synthesis of α-GOSs by immobilized α-galactosidase for the first time, laying a foundation for industrial applications in the future. The α-galactosidase from Aspergillus niger L63 was immobilized as cross-linked enzyme aggregates (CLEAs) nano-biocatalyst through enzyme precipitating and cross-linking steps without using carriers. Among the tested agents, the ammonium sulfate showed high precipitation efficacy and induced regular structures of α-galactosidase CLEAs (Aga-CLEAs) that had been analyzed by scanning electron microscopy and Fourier-transform infrared spectroscopy. Through optimization by response surface methodology, the ammonium sulfate-induced Aga-CLEAs achieved a high activity recovery of around 90% at 0.55 U/mL of enzymes and 36.43 mM glutaraldehyde with cross-linking for 1.71 h. Aga-CLEAs showed increased thermal stability and organic solvent tolerance. The storage ability was also improved since it maintained 74.5% activity after storing at 4 °C for three months, significantly higher than that of the free enzyme (21.6%). Moreover, Aga-CLEAs exhibited excellent reusability in the α-GOSs synthesis from galactose, retaining above 66% of enzyme activity after 10 batch reactions, with product yields all above 30%.

Magnetic Cross-Linked Enzyme Aggregates of a Transpeptidase-Specialized Variant (N450D) of Bacillus licheniformis γ-Glutamyl Transpeptidase: An Efficient and Stable Biocatalyst for l-Theanine Synthesis

γ-Glutamyl transpeptidase (GGT) catalyzes the transfer of glutathione’s γ-glutamyl group and related γ-glutamyl amides to water, amino acids or peptides, and utilizes a conserved Thr residue to process its own polypeptide chain into a large and a small subunit that then assemble to produce a catalytically competent enzyme. In this study, the magnetic cross-linked enzyme aggregates (mCLEAs) of a transpeptidase-specialized variant (N450D) of Bacillus licheniformis GGT were successfully prepared with optimized process parameters viz.1.25:1 (v/v) of isopropanol to N450D (0.3 mg/mL) ratio/0.02:1 (w/w) of enzyme to 3-aminopropyl triethoxysilane (APTES)-coated magnetic nanoparticle ratio/20 mM of glutaraldehyde. The prepared magnetic nanoparticles and immobilized enzyme (N450D-mCLEAs) were characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, field-emission scanning electron microscope integrated with energy dispersive X-ray spectroscopy (FESEM/EDS), and superparamagnetic analysis. As compared with free enzyme, N450D-mCLEAs displayed significantly higher heat resistance at temperatures of 55 and 60 °C, and had a greater stability over a storage period of one month. The immobilized enzyme could also be reused for 10 consecutive biocatalytic cycles with no significant reduction in the percent yield of l-theanine. Conclusively, this immobilization strategy surely provides a meaningful glance of developing N450D-mediated biocatalysis for the production of physiologically important γ-glutamyl compounds.

Preparation, characterization and stability studies of cross-linked α-amylase aggregates (CLAAs) for continuous liquefaction of starch

In current study, α-amylase of fungal origin was immobilized using cross-linking strategy. The influence of precipitant (ammonium sulphate) and cross-linker (glutaraldehyde) concentration revealed that 60% (w/v) precipitant and 1.5% (v/v) cross-linker saturation was required to attain optimum activity. Cross-linked amylase aggregates (CLAAs) were characterized and 10-degree shift in optimum temperature (soluble enzyme: 50 °C; cross-linked: 60 °C) and 1-unit shift in pH (soluble enzyme: pH -6; cross-linked: pH -7) was observed after immobilization. The V_max for soluble α-amylase and its cross-linked form was 1225 U ml^-1 and 3629 U ml^-1, respectively. The CLAAs was more thermostable than its soluble form and retained its 30% activity even after 60 min of incubation at 70 °C. Moreover, cross-linked amylase retained its activity after two months while its soluble counterpart lost its complete activity after 10 and 20 days at 30 °C and 4 °C storage, respectively. Reusability test showed that cross-linked amylase could retain 13% of its residual activity after 10 repeated cycles. Therefore, 10 times more glucose was produced after cross-linking than soluble amylase when it was utilized multiple times. This study indicates that amylase aggregates are highly effective for continuous liquefaction of starch, hence have strong potential to be used for different industrial processes.

Immobilization of laccase via cross-linked enzyme aggregates prepared using genipin as a natural cross-linker

Genipin is a nontoxic natural cross-linker that was successfully used to prepare cross-linked enzyme aggregates (CLEAs) of Trametes versicolor laccase. The recovered activity of CLEAs was influenced by the co-solvent type, genipin concentration, cross-linking time, preparation pH, and bovine serum albumin (BSA; amino group feeder) concentration. The characteristics of CLEAs prepared using genipin under optimal conditions (genipin-BSA-CLEAs) were compared with those of typical CLEAs prepared using glutaraldehyde or dextran polyaldehyde. Genipin-BSA-CLEAs were nano-sized (average diameter, approximately 700 nm), had a ball-like shape, showed a narrow size distribution, and exhibited the highest substrate affinity among the prepared CLEAs. The thermal stability of genipin-BSA-CLEAs was 6.8-fold higher than that of free laccase, and their pH stability was also much higher than that of free laccase in the tested range. Additionally, genipin-BSA-CLEAs retained 85% of their initial activity after 10 cycles of reuse. Particularly, genipin-BSA-CLEAs showed higher thermal and pH stability than CLEAs that were cross-linked using glutaraldehyde. Therefore, genipin represents an alternative to toxic compounds such as glutaraldehyde during cross-linking to prepare CLEAs.

Preparation of highly diffusible porous cross-linked lipase B from Candida antarctica conjugates: Advances in mass transfer and application in transesterification of 5-Hydroxymethylfurfural

The present work pronounces the three phase partitioning (TPP)-facilitated preparation of porous cross-linked Candida antarctica lipase B (CaLB) aggregates (pCLEAs) for 5-Hydroxymethylfurfural (HMF) esters synthesis. CLEAs and pCLEAs of CaLB were prepared with eupergit as the support under the optimized conditions of pH 8.0, eupergit/protein ratio of 3.0:1.0, 50 mM cross-linker concentration and 3.3 mg/mL BSA concentration in 4 h. The optimum starch concentration for pCLEAs was 0.20%, m/v. The maximum biocatalytic load was 650 U/g (CLEAs) and 721 U/g (pCLEAs), and the immobilized biocatalysts were stable over a pH range of 6.0-9.0 and temperature range of (40-60)°C. The BET surface area of CLEAs and pCLEAs were 21.3 and 29.1 m²/g, respectively, and the catalytic efficiency of pCLEAs was 2.2-fold higher than that of CLEAs. Subsequently, the pCLEAs of CaLB were utilized for the manufacturing of industrially significant HMF esters. Under the optimized transesterification conditions, HMF conversion with pCLEAs CaLB was 1.41- and 1.25-fold higher than with free and CLEAs CaLB, respectively. The pCLEAs were reused upto 8 consecutive transesterification cycles and the produced HMF esters reduced the surface tension of water from 72 mN/m to 32.6 mN/m, proving its potential application as surface-active compounds.

Preparation and synthetic dye decolorization ability of magnetic cross-linked enzyme aggregates of laccase from Bacillus amyloliquefaciens

Laccases are versatile oxidases that are capable of decolorizing various synthetic dyes. Recombinant Bacillus amyloliquefaciens laccase was immobilized as magnetic cross-linked enzyme aggregates (M-CLEAs) for application in dye decolorization. Several parameters influencing the activity recovery were evaluated during the synthesis of M-CLEAs. With ammonium sulfate as precipitant, maximum activity was recovered by cross-linking with 0.16% glutaraldehyde for 1 h. The prepared M-CLEAs exhibited improved activity under alkaline conditions. It remained 74% activity after incubation at 60 °C for 5 h. Enhanced tolerance towards NaCl was also observed for the M-CLEAs, with 68% activity remaining in the presence of 1 M NaCl. The immobilized laccase could rapidly decolorize more than 93% of reactive black 5 and indigo carmine in 1 h, while its catalytic efficiency towards reactive blue 19 was relatively low. After four cycles of consecutive reuse, the M-CLEAs could decolorize 92% of indigo carmine. The easy recovery and reusability of M-CLEAs facilitate the potential application of bacterial laccase in dye decolorization.

Combination of Adsorption and Cellulose Derivative Membrane Coating for Efficient Immobilization of Laccase

Immobilization of enzyme based on combination of adsorption and cellulose derivative membrane coating was established in this work for the first time. Laccase, a commonly used enzyme in varied fields, was chosen as the model enzyme to demonstrate this method. After investigating operational conditions, the optimal process was obtained as follows: diatomite or HPD-417 as the adsorption carrier, 0.5% (w/v) methylcellulose (40,000~50,000) acetone solution as the coating solution, 0.75% (w/v) polyethylene glycol or maltose as the protective agent, and drying at 4 °C for 9 h. Under the optimal conditions, the residual activities of diatomite and HPD-417 immobilized laccase reached 99.33% and 94.15%, respectively. The study on properties showed that the immobilized laccases held high pH tolerance and thermal stability. The immobilized laccases were further applied to the indigo decolorization and 2, 4-dichlorophenol degradation. They showed high catalytic efficiency and could be reused for several batches. On the whole, the immobilization method developed in this work can effectively avoid the inactivation of laccase during immobilization and improve the stability of immobilized laccase. The laccase immobilized by this method shows obvious potential for environmental governance.

Biocatalytic Oxidation of Alcohols

Enzymatic methods for the oxidation of alcohols are critically reviewed. Dehydrogenases and oxidases are the most prominent biocatalysts, enabling the selective oxidation of primary alcohols into aldehydes or acids. In the case of secondary alcohols, region and/or enantioselective oxidation is possible. In this contribution, we outline the current state-of-the-art and discuss current limitations and promising solutions.

Removal of bisphenol A in aqueous solution using magnetic cross-linked laccase aggregates from Trametes hirsuta

Enzymatic removal of Bisphenol A (BPA), acknowledged as an environmentally friendly approach, is a promising method to deal with hard degradable contaminants. However, the application of "enzymatic treatment" has been limited due to lower operational stability and practical difficulties associated with recovery and recycling. Enzyme immobilization is an innovative approach which circumvents these drawbacks. In this study, laccase from Trametes hirsuta was used for BPA removal. Amino-functionalized magnetic Fe3O4 nanoparticles were synthesized via the co-precipitation method followed by surface modification with (3-aminopropyl)trimethoxysilane (APTMS). The as-prepared nanoparticles were utilized for the immobilization of laccase with the magnetic cross-linked enzyme aggregates method (MCLEAs). Activity recovery of 27% was achieved, while no immobilized laccase was observed in the cross-linked enzyme aggregates method. The performance of immobilized laccase was measured by analyzing the degradation of BPA pollutant. The maximum removal efficiency of 87.3% was attained with an initial concentration of 60 ppm throughout 11 h.

Extraction and crosslinking of bromelain aggregates for improved stability and reusability from pineapple processing waste

The present study is first of its kind that focuses upon the extraction of bromelain from pineapple core waste and stabilising it as insoluble cross-linked aggregates. The influence of process variables such as the choice of precipitant, type of cross-linker, concentration of cross-linker and the reaction time for cross-linking step was investigated upon the activity recovery of bromelain cross-linked aggregates. The optimization of this biocatalyst preparation specifically recovered 87% of the enzymatic activity available in pineapple core waste by ammonium sulphate (60%, w/v) precipitation followed by cross-linking for 4 h with 80 mM glutaraldehyde. Cross-linked bromelain aggregates were thermally more stable and exhibited higher pH stability in comparison to free bromelain. The cross-linked bromelain aggregates exhibited higher operational stability in different organic solvents at 4 °C. The highest operational stability (% stability given in parenthesis) was observed in acetone (100%) followed by hexane (53.6%), ethyl acetate (39.6%), ethanol (32.5%) and chloroform (14.9%). The kinetic studies revealed higher Km value (5.45 mM) after the formation of cross-linked bromelain aggregates as compared to free bromelain (5.04 mM) with almost similar Vmax values. Cross-linked bromelain aggregates also showed significant reusability characteristics with an activity retention of >85% after 5-time cycles. Such recyclability of bromelain cross-linked aggregates could lead to potential industrial applications in both food and non-food sector. In addition, the present extraction method avoids costs related to purification and expensive immobilization carriers.

Catalytic Oxidations in a Bio-Based Economy

The role of bio- and chemo-catalytic aerobic oxidations in the production of commodity chemicals in a bio-refinery is reviewed. The situation is fundamentally different to that in a petrochemicals refinery where the feedstocks are gaseous or liquid hydrocarbons that are oxidized at elevated temperatures in the vapor or liquid phase under solvent-free conditions. In contrast, the feedstocks in a biorefinery are carbohydrates that are water soluble solids and their conversion will largely involve aerobic oxidations of hydroxyl functional groups in water as the solvent under relatively mild conditions of temperature and pressure. This will require the development and use of cost-effective and environmentally attractive processes using both chemo- and biocatalytic methods for alcohols and polyols.

Compartmentalized cross-linked enzymatic nano-aggregates (c-CLEnA) for efficient in-flow biocatalysis

Nano-sized enzyme aggregates, which preserve their catalytic activity are of great interest for flow processes, as these catalytic species show minimal diffusional issues, and are still sizeable enough to be effectively separated from the formed product. The realization of such catalysts is however far from trivial. The stable formation of a micro-to millimeter-sized enzyme aggregate is feasible via the formation of a cross-linked enzyme aggregate (CLEA); however, such a process leads to a rather broad size distribution, which is not always compatible with microflow conditions. Here, we present the design of a compartmentalized templated CLEA (c-CLEnA), inside the nano-cavity of bowl-shaped polymer vesicles, coined stomatocytes. Due to the enzyme preorganization and concentration in the cavity, cross-linking could be performed with substantially lower amount of cross-linking agents, which was highly beneficial for the residual enzyme activity. Our methodology is generally applicable, as demonstrated by using two different cross-linkers (glutaraldehyde and genipin). Moreover, c-CLEnA nanoreactors were designed with Candida antarctica Lipase B (CalB) and Porcine Liver Esterase (PLE), as well as a mixture of glucose oxidase (GOx) and horseradish peroxidase (HRP). Interestingly, when genipin was used as cross-linker, all enzymes preserved their initial activity. Furthermore, as proof of principle, we demonstrated the successful implementation of different c-CLEnAs in a flow reactor in which the c-CLEnA nanoreactors retained their full catalytic function even after ten runs. Such a c-CLEnA nanoreactor represents a significant step forward in the area of in-flow biocatalysis.

c-CLEnA are obtained via cross-linking enzymes in the nanocavity of supramolecular stomatocytes. Such c-CLEnA can be recycled while retaining its activity – an excellent nanoreactors platform for in-flow bio-catalysis.

Immobilization of Enzymes as Cross-Linked Enzyme Aggregates: General Strategy to Obtain Robust Biocatalysts

Among carrier-free immobilization techniques, cross-linked enzyme aggregates (CLEA) have been extensively described for a great number of diverse enzymes. During the last two decades, numerous efforts have been devoted to identify and understand the main variables involved in CLEA's preparation process leading to robust immobilized biocatalysts. Since every enzyme immobilized as CLEA requires specific conditions and protocols, herein we provide a general preparation strategy where main parameters are highlighted and correlated with a possible desired improved enzyme feature.

Combined cross-linked enzyme aggregates of glycerol dehydrogenase and NADH oxidase for high efficiency in situ NAD+ regeneration

Cofactor regeneration is an important method to avoid the consumption of large quantities of oxidized cofactor NAD⁺ in enzyme-catalyzed reactions. Herein, glycerol dehydrogenase (GDH) and NADH oxidase preparations by aggregating enzymes with ammonium sulphate followed by cross-linking formed aggregates for effective regeneration of NAD⁺. After optimization, the activity of combi-CLEAs and separate CLEAs mixtures were 950 and 580 U/g, respectively. And the catalytic stability of combi-CLEAs against pH and temperature was superior to the free enzyme mixture. After ten cycles of reuse, the catalytic efficiency could still retain 63.3% of its initial activity, indicating that the constructed combi-CLEAs system had excellent reusability. Also, the conversion of glycerol to 1,3-dihydroxyacetone (DHA) was improved by the constructed NAD⁺ regeneration system, resulting in 4.6%, which was 2.5 times of the free enzyme system. Thus, wide applications of this co-immobilization method in the production of various chiral chemicals could be expected in the industry for its high efficiency at a low cost.

Cross-linked α-galactosidase aggregates: optimization, characterization and application in the hydrolysis of raffinose-type oligosaccharides in soymilk

BACKGROUND

Cross-linked enzyme aggregates (CLEAs) of α-galactosidase, partially purified from maize (Zea mays) flour, were prepared. The impact of various parameters on enzyme activity was examined to optimize the immobilization procedure. Biochemical characterization of the free and immobilized enzyme was carried out. Stability (thermal, pH, storage and operational stability) and reusability tests were performed. The potential use of the free enzyme and the CLEAs in hydrolysis processes of raffinose-type oligosaccharides present in soymilk was investigated.

RESULTS

α-galactosidase CLEAs were prepared with 47% activity recovery under optimum conditions [1:5 (v/v) enzyme solution:saturated ammonium sulfate solution ratio; 7.5 mg protein and 0.1% (v/v) glutaraldehyde, 6 h, 4 °C, 150 rpm]. α-galactosidase CLEAs exhibited increased stability in comparison to the free enzyme. The CLEAs and the free enzyme showed a maximum activity at 40°C and their optimal pH values were5.5 and 6.0, respectively. Kinetic constants (K_M , V_max and k_cat ) were calculated for the free enzyme and the CLEAs in the presence of p-nitrophenyl-α-d-galactopyranoside, stachyose, melibiose and raffinose. The effect of various chemicals and sugars on enzyme activity showed that both enzyme forms were significantly inhibited by HgCl₂ and galactose. The CLEAs hydrolyzed 85% of raffinose and 96% of stachyose.

CONCLUSION

The α-galactosidase CLEAs, with their satisfactory enzymatic characteristics, have much potential for use in the food and feed industry. © 2019 Society of Chemical Industry.

Tackling the Challenges of Enzymatic (Bio)Fuel Cells

The ever-increasing demands for clean and sustainable energy sources combined with rapid advances in biointegrated portable or implantable electronic devices have stimulated intensive research activities in enzymatic (bio)fuel cells (EFCs). The use of renewable biocatalysts, the utilization of abundant green, safe, and high energy density fuels, together with the capability of working at modest and biocompatible conditions make EFCs promising as next generation alternative power sources. However, the main challenges (low energy density, relatively low power density, poor operational stability, and limited voltage output) hinder future applications of EFCs. This review aims at exploring the underlying mechanism of EFCs and providing possible practical strategies, methodologies and insights to tackle these issues. First, this review summarizes approaches in achieving high energy densities in EFCs, particularly, employing enzyme cascades for the deep/complete oxidation of fuels. Second, strategies for increasing power densities in EFCs, including increasing enzyme activities, facilitating electron transfers, employing nanomaterials, and designing more efficient enzyme-electrode interfaces, are described. The potential of EFCs/(super)capacitor combination is discussed. Third, the review evaluates a range of strategies for improving the stability of EFCs, including the use of different enzyme immobilization approaches, tuning enzyme properties, designing protective matrixes, and using microbial surface displaying enzymes. Fourth, approaches for the improvement of the cell voltage of EFCs are highlighted. Finally, future developments and a prospective on EFCs are envisioned.