Cross-linked enzyme aggregates (CLEAs) of Pencilluim notatum lipase enzyme with improved activity, stability and reusability characteristics

Magnetic nanoflowers: a hybrid platform for enzyme immobilization

The use of organic-inorganic hybrid nanoflowers as a support material for enzyme immobilization has gained significant attention in recent years due to their high stability, ease of preparation, and enhanced catalytic activity. However, a major challenge in utilizing these hybrid nanoflowers for enzyme immobilization is the difficulty in handling and separating them due to their low density and high dispersion. To address this issue, magnetic nanoflowers have emerged as a promising alternative enzyme immobilization platform due to their easy separation, structural stability, and ability to enhance catalytic efficiency. This review focuses on different methods for designing magnetic nanoflowers, as well as future research directions. Additionally, it provides examples of enzymes immobilized in the form of magnetic nanoflowers and their applications in environmental remediation, biosensors, and food industries. Finally, the review discusses possible ways to improve the material for enhanced catalytic activity, structural stability, and scalability.

Improvement of combined cross-linked enzyme aggregates of cyclodextrin glucanotransferase and maltogenic amylase by functionalization of cross-linker for maltooligosaccharides synthesis

Combined cross-linked enzyme aggregates of cyclodextrin glucanotransferase (CGTase) and maltogenic amylase (Mag1) from Bacillus lehensis G1 (Combi-CLEAs-CM) were successfully developed to synthesis maltooligosaccharides (MOS). Yet, the poor cross-linking performance between chitosan (cross-linker) and enzymes resulting low activity recovery and catalytic efficiency. In this study, we proposed the functionalization of cross-linkers with the integration of computational analysis to study the influences of different functional group on cross-linkers in combi-CLEAs development. From in-silico analysis, O-carboxymethyl chitosan (OCMCS) with the highest binding affinity toward both enzymes was chosen and showed alignment with the experimental result, in which OCMCS was synthesized as cross-linker to develop improved activity recovery of Combi-CLEAs-CM-ocmcs (74 %). The thermal stability and deactivation energy (205.86 kJ/mol) of Combi-CLEAs-CM-ocmcs were found to be higher than Combi-CLEAs-CM (192.59 kJ/mol). The introduction of longer side chain of carboxymethyl group led to a more flexible structure of Combi-CLEAs-CM-ocmcs. This alteration significantly reduced the Km value of Combi-CLEAs-CM-ocmcs by about 3.64-fold and resulted in a greater Kcat/Km (3.63-fold higher) as compared to Combi-CLEAs-CM. Moreover, Combi-CLEAs-CM-ocmcs improved the reusability with retained >50 % of activity while Combi-CLEAs-CM only 36.18 % after five cycles. Finally, maximum MOS production (777.46 mg/g) was obtained by Combi-CLEAs-CM-ocmcs after optimization using response surface methodology.

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.

Site-directed immobilization of enzymes on nanoparticles using self-assembly systems

Enzyme immobilization is an effective method for improving the stability and reusability. However, linking at random sites on the enzyme results in low catalytic efficiency due to blockage of the active site or conformational changes. Therefore, controlling the orientation of enzymes on the carrier has been developed. Here, the site-specific mutation and the SpyTag/SpyCatcher systems were used to prepare a site-directed immobilized enzyme. The thermal stability of the immobilized enzyme was better than that of the free enzyme, and ≥80 % of the catalytic activity was retained after 30 days of storage. Furthermore, the Michaelis constant (Km) and the turnover number (kcat) of the immobilized enzyme were 5.23-fold lower and 6.11-fold higher than those of the free enzyme, respectively, which appeared to be related to changes in secondary structure after immobilization. These findings provide a new and effective option for enzyme-directed immobilization.

Combined cross-linking of Rhizomucor miehei lipase and Candida antarctica lipase B for the effective enrichment of omega-3 fatty acids in fish oil

The incorporation of a non-specific lipase and a sn-1,3 specific one in a single immobilized system can be a promising approach for the exploitation of both lipases. A one-step immobilization platform mediated by an isocyanide-based multi-component reaction was applied to create co-cross-linked enzymes (co-CLEs) of lipases from Rhizomucor miehei (sn-1,3 specific) and Candida antarctica (non-specific). Glutaraldehyde was found to be effective cross-linker by producing specific activity of 16.9 U/mg and immobilization yield of 99 %. High activity recovery of up to 404 % was obtained for immobilized derivatives. Leaking experiment showed covalent nature of the cross-linking processes. BSA had considerable effect on the immobilization process, providing 87-100 % immobilization yields and up to 10 times improvement in the specific activity of the immobilized derivatives. Scanning electron microscopy images showed flower-like and rod-like structures for the CLEs prepared by glutaraldehyde and undecanedicarboxylic acid, respectively. The prepared co-CLEs were examined in non-selective enrichment of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from fish oil, showing capability of releasing up to 100 % of both omega-3 fatty acids within 8 h of the reaction. The reusability of co-CLEs in five successive cycles presented retaining 63-72 % of their initial activities after the fifth reuse cycle in the hydrolysis reaction.

An Overview of Crosslinked Enzyme Aggregates: Concept of Development and Trends of Applications

Enzymes are commonly used as biocatalysts for various biological and chemical processes in industrial applications. However, their limited operational stability, catalytic efficiency, poor reusability, and high-cost hamper further industrial usage. Thus, crosslinked enzyme aggregates (CLEAs) are developed as a better enzyme immobilization tool to extend the enzymes' operational stability. This immobilization method is appealing because it is simpler due to the absence of ballast and permits the collective use of crude enzyme cocktails. CLEAs, so far, have been successfully developed using a variety of enzymes, viz., hydrolases, proteases, amidases, lipases, esterases, and oxidoreductase. Recent years have seen the emergence of novel strategies for preparing better CLEAs, which include the combi- and multi-CLEAs, magnetics CLEAs, and porous CLEAs for various industrial applications, viz., laundry detergents, organic synthesis, food industries, pharmaceutical applications, oils, and biodiesel production. To better understand the different strategies for CLEAs' development, this review explores these strategies and highlights the relevant concerns in designing innovative CLEAs. This article also details the challenges faced during CLEAs preparation and solutions for overcoming them. Finally, the trending strategies to improve the preparation of CLEAs alongside their industrial application trends are also discussed.

Innovative biocatalyst synthesis of pectinolytic enzymes by cross-linking strategy: Potentially immobilised pectinases for the production of pectic-oligosaccharides from pectin

Pectinases are outstanding multienzymes, which have the potential to produce new emerging pectic-oligosaccharides (POS) via enzymatic hydrolysis of pectin. However, free pectinase is unable to undergo repeated reaction for the production of POS. This study proposed a sustainable biocatalyst of pectinases known as cross-linked pectinase aggregates (CLPA). Pectinase from Aspergillus aculeatus was successfully precipitated using 2 mg/mL pectinase and 60 % acetone for 20 min at 20 °C, which remained 36.3 % of its initial activity. The prepared CLPA showed the highest activity recovery (85.0 %), under the optimised conditions (0.3 % (v/v) starch and glutaraldehyde mixture (St/Ga), 1.5: 1 of St/Ga, 25 °C, 1.5 h). Furthermore, pectin-degrading enzymes from various sources were used to produce different CLPA. The alteration of pectinase secondary structure gave high stability in acidic condition (pH 4), thermostability, deactivation energy and half-life, and improved storage stability at 4 °C for 30 days. Similarly to their free counterpart, the CLPA exhibited comparable enzymatic reaction kinetics and could be reused eight times with approximately 20 % of its initial activity. The developed CLPA does not only efficaciously produced POS from pectin as their free form, but also exhibited better operational stability and reusability, making it more suitable for POS production.

Performance of cross-linked enzyme crystals of engineered halohydrin dehalogenase HheG in different chemical reactor systems

Halohydrin dehalogenase HheG is an industrially interesting biocatalyst for the preparation of different β-substituted alcohols starting from bulky internal epoxides. We previously demonstrated that the immobilization of different HheG variants in the form of cross-linked enzyme crystals (CLECs) yielded stable and reusable enzyme immobilizes with increased resistance regarding temperature, pH, and the presence of organic solvents. Now, to further establish their preparative applicability, HheG D114C CLECs cross-linked with bis-maleimidoethane have been successfully produced on a larger scale using a stirred crystallization approach, and their application in different chemical reactor types (stirred tank reactor, fluidized bed reactor, and packed bed reactor) was systematically studied and compared for the ring opening of cyclohexene oxide with azide. This revealed the highest obtained space-time yield of 23.9 kgproduct  gCLEC -1  h-1  Lreactor volume -1 along with the highest achieved product enantiomeric excess [64%] for application in a packed-bed reactor. Additionally, lyophilization of those CLECs yielded a storage-stable HheG preparation that still retained 67% of initial activity (after lyophilization) after 6 months of storage at room temperature.

Robust cross-linked cyclodextrin glucanotransferase from Bacillus lehensis G1 aggregates using an improved cross-linker and a new co-aggregant for the production of cyclodextrins

One of the potentials of carrier-free cross-linked enzyme aggregates (CLEA) immobilization is the ability to be separated and reuse. Yet, it might be impeded by the poor mechanical stability resulting low recyclability. CLEA of CGTase from Bacillus lehensis G1 (CGTase G1-CLEA) using chitosan (CS) as a cross-linker demonstrated high activity recovery however, displayed poor reusability. Therefore, the relationship between mechanical strength and reusability is studied by enhancing the CS mechanical properties and applying a new co-aggregation approach. Herein, CS was chemically cross-linked with glutaraldehyde (GA) and GA was introduced as a co-aggregant (coGA). CGTase G1-CLEA developed using an improved synthesized chitosan-glutaraldehyde (CSGA) cross-linker and a new coGA technique showed to increase its mechanical stability which retained 63.4% and 52.2%, respectively compared to using CS that remained 33.1% of their initial activity after stirred at 500 rpm. The addition of GA impacted the morphology and interaction consequently stabilizing the CLEAs durability in production of cyclodextrins. As a result, the reusability of CGTase G1-CLEA with CSGA and coGA increased by 56.6% and 42.8%, respectively compared to previous CLEA after 5 cycles for 2 h of reaction. This verifies that the mechanical strength of immobilized enzyme influences the improvement of its operational stability.

Adsorption-precipitation-cross-linking immobilization of GDSL-type esterase from Aspergillus niger GZUF36 by polydopamine-modified magnetic clarity tetroxide nanocouplings and its enzymatic characterization

Recombinant INANE1 (rINANE1), a recombinant intracellular GDSL-type esterase from Aspergillus niger GZUF36, has high acetate substrate specificity. Here, rINANE1 was successfully immobilized on polydopamine (PDA)-modified magnetic ferric oxide nanoparticles (Fe₃O₄NPs) by adsorption-precipitation-cross-linking to obtain cross-linked enzyme aggregate (CLEA)-rINANE1-Fe₃O₄@PDA. Fe₃O₄, Fe₃O₄@PDA, and CLEA-rINANE1-Fe₃O₄@PDA were characterized by scanning electron microscopy, X-ray diffraction, vibrating-sample magnetometry, Fourier transform infrared (FTIR) spectroscopy, and zeta potential analysis. Upon immobilization, CLEA-rINANE1-Fe₃O₄@PDA, with a protein loading of 72.72 ± 1.01 mg/g, reached optimal activity recovery of 104.40 % ± 1.14 %. FTIR analysis showed that immobilization increased the relative content of β-folding in rINANE1 by 12.25 % and reduced irregular curl by 4.16 %, rendering the structure more orderly. Specifically, under an alkaline condition (pH 10), CLEA-rINANE1-Fe₃O₄@PDA performed over 100 % of initial activity. The optimum temperature increased by 5 °C, and over 55 % of the initial activity was observed after 12 h at 55 °C. CLEA-rINANE1-Fe₃O₄@PDA showed over 40 % of its relative activity, whereas free rINANE1 showed <10 % in acetonitrile. In addition, the relative activity of CLEA-rINANE1-Fe₃O₄@PDA was retained at about 80 % after eight cycles and maintained at 109 % after 45 days. The PDA-modified magnetic ferrite nanoparticles exhibited excellent stability and recyclability, providing a new avenue for developing industrial biocatalysts.

Combined cross-linked enzyme aggregates of cyclodextrin glucanotransferase and maltogenic amylase from Bacillus lehensis G1 for maltooligosaccharides synthesis

Maltooligosaccharides (MOS) are functional oligosaccharides that can be synthesized through enzymatic cascade reaction between cyclodextrin glucanotransferase (CGTase) and maltogenic amylase (Mag1) from Bacillus lehensis G1. To address the problems of low operational stability and non-reusability of free enzymes, both enzymes were co-immobilized as combined cross-linked enzyme aggregates (Combi-CLEAs-CM) with incorporation of bovine serum albumin (BSA) and Tween 80 (Combi-CLEAs-CM-add). Combi-CLEAs-CM and Combi-CLEAs-CM-add showed activity recoveries of 54.12 % and 69.44 %, respectively after optimization. Combi-CLEAs-CM-add showed higher thermal stability at higher temperatures (40 °C) with longer half-life (46.20 min) as compared to those of free enzymes (36.67 min) and Combi-CLEAs-CM (41.51 min). Both combi-CLEAs also exhibited higher pH stability over pH 5 to pH 9, and displayed excellent reusability with >50 % of initial activity retained after four cycles. The reduction in K_m value of about 22.80 % and 1.76-fold increase in starch hydrolysis in comparison to Combi-CLEAs-CM attested the improvement of enzyme-substrate interaction by Tween 80 and pores formation by BSA in Combi-CLEAs-CM-add. The improved product specificity of Combi-CLEAs-CM-add also produced the highest yield of MOS (492 mg/g) after 3 h. Therefore, Combi-CLEAs-CM-add with ease of preparation, excellent reusability and high operational stability is believed to be highly efficacious biocatalyst for MOS production.

Dephytinization of wheat and rice bran by cross-linked enzyme aggregates of Mucor indicus phytase: a viable prospect for food and feed industries

BACKGROUND

Novel feeds for improved feed intake and for enhanced nutrient bioavailability have recently attracted attention. Insoluble dietary fibers, especially rice and wheat bran, have generated much interest due to their nutritional value. Incorporating insoluble dietary fiber into diets could be a viable way to maximize the feed conversion ratio.

RESULTS

Cross-linked phytase aggregates (CLPA) were synthesized by precipitating enzymes followed by cross-linking with 5 mmol L^-1 glutaraldehyde, yielding 88.24 (U g^-1 ) of enzyme load without the assistance of a proteic feeder. The epitome of the study is the dephosphorylation of wheat bran and rice bran by varying pH, enzyme concentration, and temperature. The highest inorganic phosphorus liberation by 150 U L-^-1 of free phytase was 23.72 (wheat bran) and 48.08 mg g^-1 (rice bran) after 12 h of incubation.  Furthermore, 150 U L^-1 of CLPA liberated 28.72 (wheat bran) and 52.08 mg g^-1 (rice bran) of inorganic phosphorus with an incubation time of 12 h.

CONCLUSION

Thermostable free phytase was insolubilized to dephosphorylate the agro-residue, namely, wheat bran and rice bran, to reduce the anti-nutritional factor (the phytate content) of these insoluble dietary fibers. © 2022 Society of Chemical Industry.

Immobilization of lipase on silica nanoparticles by adsorption followed by glutaraldehyde cross-linking

In this study, Candida antarctica lipase B was immobilized on silica (SiO₂) nanoparticles by physical adsorption, and then cross-linked with glutaraldehyde (GA) to prepare cross-linked immobilized lipase (CLIL). During the condition of 1.28 mg/mL lipase concentration, 25 ℃ temperature, 2 h adsorption time, 0.01% GA (V/V) 7.5 mL and 2 h cross-linking time, the highest recovery activity of CLIL reached 87.82 ± 0.07% (22.55 ± 0.025 U/mg). Scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM) confirmed that lipase was immobilized on the surface of SiO₂ nanoparticles. The changes in secondary structures of CLIL indicated that cross-linking changed the secondary structure of lipase protein, which made the structure of CLIL more stable. Compared with the free lipase, the thermal stability and storage stability of CLIL was significantly improved, and the t_1/2 at 60 °C was extended. Studies had shown that it was a feasible method to obtain CLIL by cross-linking after adsorbing lipase on SiO₂ nanoparticles.

Crystal Contact Engineering for Enhanced Cross-Linking Efficiency of HheG Crystals

The generation of cross-linked enzyme crystals is a very attractive method for immobilization of enzymes displaying high crystalizability. However, the commonly used cross-linker glutaraldehyde is not always compatible with enzyme activity. Therefore, we previously reported the engineering of halohydrin dehalogenase HheG from Ilumatobacter coccineus to enable thiol-specific cross-linking during CLEC generation by insertion of cysteine residues in the crystal contact. To broaden the applicability of this approach, herein crystal contact engineering of HheG has been performed to incorporate additional lysine residues as defined cross-linking sites for CLEC generation. Using the primary amine-specific cross-linker dithiobis(succinimidyl propionate) (DSP), CLECs of HheG variant V46K were obtained that displayed a high gain in thermal stability compared to wild-type HheG, while using only a low cross-linker concentration. Moreover, respective V46K CLECs exhibited a 10 K higher reaction temperature optimum as well as significantly improved activity and stability at acidic pH and in the presence of organic co-solvents. Overall, our study demonstrates that lysine-specific cross-linkers can also be used as an alternative to glutaraldehyde for stable CLEC generation of halohydrin dehalogenases, and that cross-linking efficiency is significantly improved upon crystal contact engineering.

Cross-linked cyclodextrin glucanotransferase aggregates from Bacillus lehensis G1 for cyclodextrin production: Molecular modeling, developmental, physicochemical, kinetic and thermodynamic properties

Type of cross-linking agents influence the stability and active cross-linked enzyme aggregates (CLEA) immobilization. The information of molecular interaction between enzyme-cross linker is not well explored thus screening wide numbers of cross-linker is crucial in CLEA development. This study combined the molecular modeling and experimental optimization to investigate the influences of different cross-linking agents in developing CLEA of cyclodextrin glucanotranferase G1 (CGTase G1) for cyclodextrins (CDs) synthesis. Seven types of cross-linkers were tested and CGTase G1 cross-linked with chitosan (CS-CGTG1-CLEA) displayed the highest activity recovery (84.6 ± 0.26%), aligning with its highest binding affinity, radius of gyration and flexibility through in-silico analysis towards CGTase G1. CS-CGTG1-CLEA was characterized and showed a longer half-life (30.06 ± 1.51 min) and retained a greater thermal stability (52.73 ± 0.93%) after 30 min incubation at optimal conditions compared to free enzyme (10.30 ± 1.34 min and 5.51 ± 2.10% respectively). CS-CGTG1-CLEA improved CDs production by 33% and yielded cumulative of 52.62 g/L CDs after five cycles for 2 h of reaction. This study reveals that abundant of hydroxyl group on chitosan interacted with CGTase G1 surface amino acid residues to form strong and stable CLEA thus can be a promising biocatalyst in CDs production.

Lipase immobilization via cross-linked enzyme aggregates: Problems and prospects - A review

In this review we have focused on the preparation of cross-linked enzyme aggregates (CLEAs) from lipases, as these are among the most used enzyme in bioprocesses. This immobilization method is considered very attractive due to preparation simplicity, non-use of supports and the possibility of using crude enzyme extracts. CLEAs provide lipase stabilization under extreme temperature or pH conditions or in the presence of organic solvents, in addition to preventing enzyme leaching in aqueous medium. However, it presents some problems in the preparation and limitations in their use. The problems in preparation refer mainly to the crosslinking step, and may be solved using an aminated feeder. The problems in handling have been tackled designing magnetic-CLEAs or trapping the CLEAs in particles with better mechanical properties, the substrate diffusion problems has been reduced by producing more porous-CLEAs, etc. The enzyme co-immobilization using combi-CLEAs is also a new tendency. Therefore, this review explores the CLEAs methodology aimed at lipase immobilization and its applications.

Instantaneous synthesis and full characterization of organic-inorganic laccase-cobalt phosphate hybrid nanoflowers

A novel approach termed the "concentrated method" was developed for the instant fabrication of laccase@Co₃(PO₄)₂•hybrid nanoflowers (HNFs). The constructed HNFs were obtained by optimizing the concentration of cobalt chloride and phosphate buffer to reach the highest activity recovery. The incorporation of 30 mM CoCl₂ and 160 mM phosphate buffer (pH 7.4) resulted in a fast anisotropic growth of the nanomaterials. The purposed method did not involve harsh conditions and prolonged incubation of precursors, as the most reported approaches for the synthesis of HNFs. The catalytic efficiency of the immobilized and free laccase was 460 and 400 M⁻¹S⁻¹, respectively. Also, the enzymatic activity of the prepared biocatalyst was 113% of the free enzyme (0.5 U mL⁻¹). The stability of the synthesized HNFs was enhanced by 400% at pH 6.5–9.5 and the elevated temperatures. The activity of laccase@Co₃(PO₄)₂•HNFs declined to 50% of the initial value after 10 reusability cycles, indicating successful immobilization of the enzyme. Structural studies revealed a 32% increase in the α-helix content after hybridization with cobalt phosphate, which improved the activity and stability of the immobilized laccase. Furthermore, the fabricated HNFs exhibited a considerable ability to remove moxifloxacin as an emerging pollutant. The antibiotic (10 mg L⁻¹) was removed by 24% and 75% after 24 h through adsorption and biodegradation, respectively. This study introduces a new method for synthesizing HNFs, which could be used for the fabrication of efficient biocatalysts, biosensors, and adsorbents for industrial, biomedical, and environmental applications.

Sortase-mediated immobilization of Candida antarctica lipase B (CalB) on graphene oxide; comparison with chemical approach

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Sortase A was used for the oriented immobilization of CalB on graphene oxide nanosheets

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Random attachment of CalB on GO nanosheets were performed by chemical immobilization

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The immobilized CalB were used for the enrichment of omega-3 fatty acids in fish oil

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The derivative obtained from oriented immobilization showed improved selectivity

In this study, Candida antarctica lipase B (CalB) was covalently immobilized on the surface of graphene oxide (GO) nanoparticles by sortase-mediated immobilization as well as a chemical attachment approach. Sortase is a transpeptidase that provides one-step purification and targeted immobilization of CalB from one specific site, presenting oriented attachment of the enzyme to a solid support. Chemical immobilization, on the other hand, is considered as a random immobilization, in which the protein can bind to the support from different regions of the protein surface. In this approach, amine-functionalized GO was further modified with glutaraldehyde to facilitate the covalent binding of CalB via its amine residues. The applied methods produced 60% and 100% immobilization yields and presented 0.106 U/mg and 0.085 U/mg of specific activities for the oriented and random immobilization, respectively. The stabilized enzyme with the sortase-mediated approach retained approximately 80% of its initial activity at 50°C.

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.

Cross-linked enzyme aggregates immobilization: preparation, characterization, and applications

Enzymes are commonly used as biocatalysts for various biological and chemical processes. However, some major drawbacks of free enzymes (e.g. poor reusability and instability) significantly restrict their industrial practices. How to overcome these weaknesses remain considerable challenges. Enzyme immobilization is one of the most effective ways to improve the reusability and stability of enzymes. Cross-linked enzyme aggregates (CLEAs) has been known as a novel and versatile carrier-free immobilization method. CLEAs is attractive due to its simplicity and robustness, without purification. It generally shows: high catalytic specificity and selectivity, good operational and storage stabilities, and good reusability. Moreover, co-immobilization of different kinds of enzymes can be acquired. These CLEAs advantages provide opportunities for further industrial applications. Herein, the preparation parameters of CLEAs were first summarized. Next, characterization of structural and catalytic properties, stability and reusability are also proposed. Finally, some important applications of this technique in: environmental protection, industrial chemistry, food industry, and pharmaceutical synthesis and delivery are introduced. Potential challenges and future research directions, such as improving cross-linking efficiency and internal mass transfer efficiency, are also presented. This implies that CLEAs provide an efficient and feasible technique to improve the properties of enzymes for use in the industry.

Enzyme Immobilization and Co-Immobilization: Main Framework, Advances and Some Applications

Enzymes are outstanding (bio)catalysts, not solely on account of their ability to increase reaction rates by up to several orders of magnitude but also for the high degree of substrate specificity, regiospecificity and stereospecificity. The use and development of enzymes as robust biocatalysts is one of the main challenges in biotechnology. However, despite the high specificities and turnover of enzymes, there are also drawbacks. At the industrial level, these drawbacks are typically overcome by resorting to immobilized enzymes to enhance stability. Immobilization of biocatalysts allows their reuse, increases stability, facilitates process control, eases product recovery, and enhances product yield and quality. This is especially important for expensive enzymes, for those obtained in low fermentation yield and with relatively low activity. This review provides an integrated perspective on (multi)enzyme immobilization that abridges a critical evaluation of immobilization methods and carriers, biocatalyst metrics, impact of key carrier features on biocatalyst performance, trends towards miniaturization and detailed illustrative examples that are representative of biocatalytic applications promoting sustainability.

Bioprospecting microbial hosts to valorize lignocellulose biomass - Environmental perspectives and value-added bioproducts

Current biorefinery approaches comprehend diverse biomass feedstocks and various conversion techniques to produce a variety of high-value biochemicals and biofuels. Lignocellulose is among the most abundant, bio-renewable, and sustainable bioresources on earth. It is regarded as a prodigious alternative raw feedstock to produce a large number of chemicals and biofuels. Producing biofuels and platform chemicals from lignocellulosic biomasses represent advantages in terms of energy and environmental perspectives. Lignocellulose is a main structural constituent of non-woody and woody plants consisting of lignin, cellulose, and hemicellulose. Efficient exploitation of all these components is likely to play a considerable contribution to the economic viability of the processes since lignocellulosic biomass often necessitate pretreatment for liberating fermentable sugars and added value products that might serve as feedstocks for microbial strains to produce biofuels and biochemicals. Developing robust microbial culture and advancements in metabolic engineering approaches might lead to the rapid construction of cell factories for the effective biotechnological transformation of biomass feedstocks to produce biorefinery products. In this comprehensive review, we discuss the recent progress in the valorization of agro-industrial wastes as prospective microbial feedstocks to produce a spectrum of high-value products, such as microbial pigments, biopolymers, industrial biocatalysts, biofuels, biologically active compounds, bioplastics, biosurfactants, and biocontrol agents with therapeutic and industrial potentialities. Lignocellulosic biomass architecture, compositional aspects, revalorization, and pretreatment strategies are outlined for efficient conversion of lignocellulosic biomass. Moreover, metabolic engineering approaches are briefly highlighted to develop cell factories to make the lignocellulose biorefinery platforms appealing.

Biocatalytic remediation of pharmaceutically active micropollutants for environmental sustainability

The discharge of an alarming number of recalcitrant pollutants from various industrial activities presents a serious threat to environmental sustainability and ecological integrity. Bioremediation has gained immense interest around the world due to its environmentally friendly and cost-effective nature. In contrast to physical and chemical methods, the use of microbial enzymes, particularly immobilized biocatalysts, has been demonstrated as a versatile approach for the sustainable mitigation of environmental pollution. Considerable attention is now devoted to developing novel enzyme engineering approaches and state-of-the-art bioreactor design for ameliorating the overall bio-catalysis and biodegradation performance of enzymes. This review discusses the contemporary and state of the art technical and scientific progress regarding applying oxidoreductase enzyme-based biocatalytic systems to remediate a vast number of pharmaceutically active compounds from water and wastewater bodies. A comprehensive insight into enzyme immobilization, the role of mediators, bioreactors designing, and transformation products of pharmaceuticals and their associated toxicity is provided. Additional studies are necessary to elucidate enzymatic degradation mechanisms, monitor the toxicity levels of the resulting degraded metabolites and optimize the entire bio-treatment strategy for technical and economical affordability.

Occurrence, environmental fate, ecological issues, and redefining of endocrine disruptive estrogens in water resources

The growing persistence of estrogenic pollutants in water resources is a worrying concern because of their endocrine disrupting activities and potentially hazardous consequences on the environmental matrices, ecology, and human health, even at low concentration. The long-term persistence of steroidal estrogens leads to their bioaccumulation in aquatic organisms that can further reach to humans via food chain route. Considering the toxicity of steroidal estrogens, it is important to mitigate these environmentally related hazardous contaminants. So far, several treatment methods, like adsorption, oxidation, irradiation, and electrochemical techniques have been proposed to eliminate estrogens from aqueous ecosystems. Nevertheless, high operational costs, insufficient removal, generation of toxic sludge, and the necessity of skilled maintenance and operating workers are the major hindrances associated with large scale applications. Bioremediation of steroidal estrogens using enzyme-based biocatalytic system has recently emerged as a promising alternative to remove and bio-transform estrogens from aqueous systems. However, the current literature lacks a critique focusing specifically and comprehensively on steroidal estrogens. The presented review is a critical assessment of the existing literature on steroid-based endocrine disruptive estrogens. A detailed description about the occurrence and eco-fate of steroidal estrogens is given with representative examples. The later half of the review stresses on the redefining (removal) of endocrine disruptive estrogens in water resources with particular reference to enzyme-based approaches.

Effect of the biological functionalization of nanoparticles on magnetic CLEA preparation

Lipase immobilization using adsorption on magnetic nanoparticles, cross-linked enzyme aggregates (CLEA), and a combination of both techniques was investigated. Experimental designs were used for the optimization of the immobilization observing that the pH and ionic strength play a principal role during the lipase immobilization and its activity. For adsorption on magnetic nanoparticles and CLEA synthesis the optimal condition was pH and 100 mM. Besides, during the CLEA synthesis, glutaraldehyde concentration showed to be a significant effect on the enzyme activity. A comparison between a magnetic CLEA prepared with (Lip@mCLEA) and without (mCLEA) biological functionalized magnetic nanoparticles was made observing that the use of functionalized support showed the best performance activity. All biocatalytic systems developed gives to the enzyme thermal stability between 45 and 70 °C, being Lip@mCLEA the more stable biocatalyst. Similar behavior was observed at different pH, where both Lip@mCLEA and mCLEA showed stability at a range of pH 5 to 8. The immobilized biocatalysts showed the same affinity of the subtract that the free enzyme suggested that the enzyme structure not modified the active site. The combination of both types of immobilization show evidenced the importance of the biological functionalization of the support when magnetic CLEA is produced.

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.

Decorated networks of native proteins: nanomaterials with tunable mesoscopic domain size

Natural and artificial proteins with designer properties and functionalities offer unparalleled opportunity for functional nanoarchitectures formed through self-assembly. However, to exploit this potential we need to design the system such that assembly results in desired architecture forms while avoiding denaturation and therefore retaining protein functionality. Here we address this challenge with a model system of fluorescent proteins. By manipulating self-assembly using techniques inspired by soft matter where interactions between the components are controlled to yield the desired structure, we have developed a methodology to assemble networks of proteins of one species which we can decorate with another, whose coverage we can tune. Consequently, the interfaces between domains of each component can also be tuned, with potential applications for example in energy - or electron - transfer. Our model system of eGFP and mCherry with tuneable interactions reveals control over domain sizes in the resulting networks.

Various type immobilizations of Isocitrate dehydrogenases enzyme on hyaluronic acid modified magnetic nanoparticles as stable biocatalysts

Magnetic nanoparticles (MNPs) were modified by hyaluronic acid (HA). After the process of functionalization, two different strategies have been used to immobilize isocitrate dehydrogenases (IDH) on MNPs. In the first strategy, cross-linked enzyme aggregates were prepared. For this, firstly hyaluronic acid modified magnetic nanoparticles cross-linked enzyme fine aggregates of isocitrate dehydrogenases (IDH/HA/MNPs-CLEAs) were synthesized, and secondly bovine serum albumin (BSA) as co-feeder was used to synthesize the IDH/BSA/HA/MNPs-CLEAs. In the second strategy, the IDH was effectively immobilized on the HA/MNPs surface. The features of MNPs and its derivatives have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), and zeta potential measurements. The activity and stability of IDH in IDH/HA/MNPs, IDH/HA/MNPs-CLEAs, and IDH/BSA/HA/MNPs-CLEAs were enhanced. Besides, the enzyme immobilized was readily separated via external magnet from the reaction medium and reused many times. The acquired findings indicate that HA/MNPs are a novel binder/support system to IDH, and IDH immobilized on this system can become a very important biocatalyst working with high accuracy and sensitivity for the determination of magnesium in drinking water and other biological solutions.

Cross-linking of carbonic anhydrase and formate dehydrogenase based on amino acid specific recognition: Conversion of carbon dioxide to formic acid

Inspired by the cascades performed in vivo, the assembly of multiple enzymes in vitro has strongly moved into the focus of researchers in the field of biocatalysis. In this study, a new, mild and accurate enzyme cross-linking method is revealed. Microbial transglutaminase (MTG) acts as a "cross-linking medium" by identifying the amide group of the glutamine and the primary amine group of lysine in the artificial peptide tags specifically to form an iso-peptide bond. Here, carbonic anhydrase (CA) and formate dehydrogenase (FDH) with different peptide tags that can be recognized by MTG were linked together to obtain different proportions of cross-linked enzymes for efficient conversion of greenhouse gas carbon dioxide to formic acid. After cross-linking, we obtained "one-to-one" and "one-to-more" cross-linked enzyme aggregates. There is a minor residual loss of the two enzymes, the remaining enzyme activity of CA is more than 93%, and the remaining enzyme activity of FDH is more than 84%. In particular, the overall catalytic efficiency of the cross-linked enzyme is increased by 5.8 times compared with free enzymes and the thermal stability of FDH at different temperatures is improved. The applied strategy demonstrates the potential application of MTG in multi-enzyme assembly and synthetic biology.

Effect of cross-linked enzyme aggregate strategy on characterization of sn-1,3 extracellular lipase from Aspergillus niger GZUF36

The sn-1,3 extracellular lipase from Aspergillus niger GZUF36 (EXANL1) has important potential applications. The cross-linked enzyme aggregate (CLEA) of purified EXANL1 (CLEA-EXANL1) achieved optimum activity recovery (148.5 ± 0.9%), immobilization yield (100 ± 0%), and recovered activity (99.7 ± 0.6%) with 80% tert-butanol as the precipitant, glutaraldehyde (GA) concentration of 30 mM, GA treatment time of 1.5 h, and centrifugal speed of 6000×g. The effect of CLEA strategy on the characterization of EXANL1 was evaluated in this work. CLEA-EXANL1 exhibited a broader optimum pH range (4-6) compared with free EXANL1 (6.5). CLEA-EXANL1 presented optimum activity at 40 °C, which was 5 °C higher than that of free EXANL1. CLEA strategy decreased the maximum reaction rate and increased the Michaelis-Menten constant of EXANL1 when olive oil emulsion was used as a substrate. Moreover, after 30 days, free EXANL1 lost more than 80.0% of its activity, whereas CLEA-EXANL1 retained more than 90.0% of its activity. CLEA strategy improved the tolerance of EXANL1 in polar organic solvents. Fourier transform infrared spectroscopy results showed that the CLEA technique increased the contents of β-sheets and β-turns in EXANL1 and reduced those of α-helixes and irregular crimps. CLEA strategy caused no change in the sn-1,3 selectivity of EXANL1. Therefore, EXANL1 in the form of CLEA is a valuable catalyst in the synthesis of 1,3-diacylglycerol. KEY POINTS: • Cross-linked enzyme aggregate (CLEA) strategy broadened the optimum pH range of sn-1,3 extracellular lipase from Aspergillus niger GZUF36 (EXANL1). • CLEA strategy improved the tolerance of EXANL1 in polar organic solvents. • CLEA strategy caused no change in the positional selectivity of EXANL1.

Extraction and reimmobilization of used commercial lipase from industrial waste

In industrial application, immobilized lipase are typically not reused and served as industrial waste after a certain process is completed. The capacity on the reusability of the spent lipase is not well studied. This current study embarks on reusing the remaining lipase from the spent immobilized enzyme. Active lipases were recovered using a simple reverse micellar extraction (RME). RME is the extraction process of targeted biomolecules using an organic solvent and a surfactant. This method was the first attempt reported on the recovery of the lipase from the used immobilized lipase. RME of the spent lipase was done using the nonionic Triton X-100 surfactant and toluene. Various parameters were optimized to maximize the lipase recovery from the used immobilized lipase. The optimum forward extraction condition was 0.075 M KCl, and backward conditions were at 0.15 M Triton X-100/toluene (pH 6, 2 M KCl) with recovery of 66%. The extracted lipase was immobilized via simple adsorption into the ethanol pretreated carrier. The optimum conditions of immobilization resulted in 96% of the extracted lipase was reimmobilized. The reimmobilized lipase was incubated for 20 h in pH 6 buffer at 50 °C of water bath shaker. The reimmobilized lipase still had 27% residual activity after 18 h of incubation, which higher thermal stability compared to the free lipase. In conclusion, the free lipase was successfully extracted from the spent immobilized lipase and reimmobilized into the new support. It exhibited high thermal stability, and the reusability of the spent lipase will promote continued use of industrial lipase and reduce the cost of the manufacturing process.

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.

Armoring bio-catalysis via structural and functional coordination between nanostructured materials and lipases for tailored applications

Nanostructured materials represent an interesting and novel class of support matrices for the immobilization of different enzymes. Owing to the high surface area, robust mechanical stability, outstanding optical, thermal, and electrical properties, nanomaterials have been rightly perceived as desired immobilization matrices for lipases immobilization with a wide array of biotechnological applications such as dairy, food technology, fine chemical, pharmaceutical, detergent, and oleochemical industries. Lipases immobilized on nanomaterials have demonstrated superior attributes than free counterparts, such as aggrandized pH and thermal stability, robustness, long-term stability, and the possibility of reuse and recycling in several times. Here we review current and state-of-the-art literature on the use of nanomaterials as novel platforms for the immobilization of lipase enzymes. The physicochemical properties and exploitation of a large number of new nanostructured materials such as carbon nanotubes, nano-silica, graphene/graphene oxide, metal nanoparticles, magnetic nanostructures, metal-organic frameworks, and hybrid nanoflowers as a host matrix to constitute robust lipases-based nanobiocatalytic systems are discussed. Conclusive remarks, trends, and future recommendations for nanomaterial immobilized enzymes are also given.

Microbial lipase: a new approach for a heterogeneous biocatalyst

Lipases are enzymes employed in several industrial process and their applicability can be increased if these biocatalysts are in the immobilize form. The objective of this work was to study the immobilization of lipase produced by submerged cultivation of Aspergillus sp. by hydrophobic interaction, evaluating its stability and reuse capacity. The immobilization process on octyl-sepharose (C₈) and octadecyl-sepabeads (C₁₈) carriers was possible after the removal of oil excess presented in the fermented broth. The results showed that the enzyme was isolated and concentrated in octyl-sepharose with 22% of the initial activity. To increase the amount of enzyme adsorbed on the carrier, 4 immobilization cycles were performed in a row, on the same carrier, with a final immobilization yield of 151.32% and an increase in the specific activity of 136%. The activity test with immobilized lipase showed that the immobilized enzyme maintained 75% of the initial activity after 20 cycles.

Nanostructured materials as a host matrix to develop robust peroxidases-based nanobiocatalytic systems

Nanostructured materials constitute an interesting and novel class of support matrices for the immobilization of peroxidase enzymes. Owing to the high surface area, robust mechanical stability, outstanding optical, thermal, and electrical properties, nanomaterials have been rightly perceived as immobilization matrices for enzyme immobilization with applications in diverse areas such as nano-biocatalysis, biosensing, drug delivery, antimicrobial activities, solar cells, and environmental protection. Many nano-scale materials have been employed as support matrices for the immobilization of different classes of enzymes. Nanobiocatalysts, enzymes immobilized on nano-size materials, are more stable, catalytically robust, and could be reused and recycled in multiple reaction cycles. In this review, we illustrate the unique structural/functional features and potentialities of nanomaterials-immobilized peroxidase enzymes in different biotechnological applications. After a comprehensive introduction to the immobilized enzymes and nanocarriers, the first section reviewed carbonaceous nanomaterials (carbon nanotube, graphene, and its derivatives) as a host matrix to constitute robust peroxidases-based nanobiocatalytic systems. The second half covers metallic nanomaterials (metals, and metal oxides) and some other novel materials as host carriers for peroxidases immobilization. The next section vetted the potential biotechnological applications of the resulted nanomaterials-immobilized robust peroxidases-based nanobiocatalytic systems. Concluding remarks, trends, and future recommendations for nanomaterial immobilized enzymes are also given.

Soluble and Cross-Linked Aggregated Forms of α-Galactosidase from Vigna mungo Immobilized on Magnetic Nanocomposites: Improved Stability and Reusability

α-Galactosidases hold immense potential due to their biotechnological applications in various industrial and functional food sectors. In the present study, soluble and covalently cross-linked aggregated forms of a low molecular weight, thermo-labile α-galactosidase from Vigna mungo (VM-αGal) seeds were immobilized onto chitosan-coated magnetic nanoparticles for improved stability and repeated usage by magnetic separation. Parameters like precipitants (type, amount, and ratio), glutaraldehyde concentration, and enzyme load were optimized for the preparation of chitosan-coated magnetic nanocomposites of cross-linked VM-αGal (VM-αGal-MC) and VM-αGal (VM-αGal-M) resulted in 100% immobilization efficiency. Size and morphology of VM-αGal-M were studied through dynamic light scattering (DLS) and scanning electron microscopy (SEM), while Fourier transform infrared spectroscopy (FTIR) was used to study the chemical composition of VM-αGal-MC and VM-αGal-M. VM-αGal-MC and VM-αGal-M were found more active in a broad range of pH (3-8) and displayed optimal temperatures up to 25 °C higher than VM-αGal. Addition of non-ionic detergents (except Tween-40) improved VM-αGal-MC activity by up to 44% but negatively affected VM-αGal-M activity. Both VM-αGal-MC (15% residual activity after 21 min at 85 °C, E_d 92.42 kcal/mol) and VM-αGal-M (69.0% residual activity after 10 min at 75 °C, E_d 39.87 kcal/mol) showed remarkable thermal stability and repeatedly hydrolyzed the substrate for 10 cycles.

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.

The Immobilization of Lipases on Porous Support by Adsorption and Hydrophobic Interaction Method

Four major enzymes commonly used in the market are lipases, proteases, amylases, and cellulases. For instance, in both academic and industrial levels, microbial lipases have been well studied for industrial and biotechnological applications compared to others. Immobilization is done to minimize the cost. The improvement of enzyme properties enables the reusability of enzymes and facilitates enzymes used in a continuous process. Immobilized enzymes are enzymes physically confined in a particularly defined region with retention to their catalytic activities. Immobilized enzymes can be used repeatedly compared to free enzymes, which are unable to catalyze reactions continuously in the system. Immobilization also provides a higher pH value and thermal stability for enzymes toward synthesis. The main parameter influencing the immobilization is the support used to immobilize the enzyme. The support should have a large surface area, high rigidity, suitable shape and particle size, reusability, and resistance to microbial attachment, which will enhance the stability of the enzyme. The diffusion of the substrate in the carrier is more favorable on hydrophobic supports instead of hydrophilic supports. The methods used for enzyme immobilization also play a crucial role in immobilization performance. The combination of immobilization methods will increase the binding force between enzymes and the support, thus reducing the leakage of the enzymes from the support. The adsorption of lipase on a hydrophobic support causes the interfacial activation of lipase during immobilization. The adsorption method also causes less or no change in enzyme conformation, especially on the active site of the enzyme. Thus, this method is the most used in the immobilization process for industrial applications.

Application of lipase immobilized on a hydrophobic support for the synthesis of aromatic esters

The present study aimed at preparing three biocatalysts via physical adsorption of lipases from Candida rugosa (CRL), Mucor javanicus, and Candida sp. on a hydrophobic and mesoporous support (Diaion HP-20). These biocatalysts were later applied to the synthesis of aromatic esters of apple peel and citrus (hexyl butyrate), apple and rose (geranyl butyrate), and apricot and pineapple (propyl butyrate). Scanning electron microscopy and gel electrophoresis confirmed a selective adsorption of lipases on Diaion, thus endorsing simultaneous immobilization and purification. Gibbs free energy (∆G) evinced the spontaneity of the process (-17.9 kJ/mol ≤ ∆G ≤ -5.1 kJ/mol). Maximum immobilized protein concentration of 30 mg/g support by CRL. This biocatalyst was the most active in olive oil hydrolysis (hydrolytic activity of 126.0 ± 2.0 U/g) and in the synthesis of aromatic esters. Maximum conversion yield of 89.1% was attained after 150 Min for the synthesis of hexyl butyrate, followed by the synthesis of geranyl butyrate (87.3% after 240 Min) and propyl butyrate (80.0% after 150 Min). CRL immobilized on Diaion retained around 93% of its original activity after six consecutive cycles of 150 Min for the synthesis of hexyl butyrate.

Designing and investigation of photo-active gellan gum for the efficient immobilization of catalase by entrapment

A photo-active gellan gum (Gel) derivative was developed by amide bond combination with trans-4-[p-(amino)styryl]pyridine (SP). The SP-Gel was cross-linked by UV curing via the intermolecular 2π + 2π cycloaddition of the inserted SP-CH=CH- moieties. The chemical structure of the obtained photo-crosslinkable biopolymer was investigated before and after the UV curing and the progress of the performed 2π + 2π cycloaddition-based cross-linking was detected via UV-visible light spectra. SP-Gel was evaluated as a polymeric matrix for the immobilization of catalase via entrapment technique. The synthesized biopolymer was mixed with the catalase and molded in the form of membranes that were UV cured to encapsulate the enzyme. The membranes were able to entrap 0.75 mg/cm² with retained activity reached above 95%. The immobilized catalase displayed higher thermal stability and higher resistance toward the environmental pH disturbances compared to the free enzyme. Also, despite the observed lower catalase-H₂O₂ affinity upon the entrapment that was indicated from the performed kinetic studies, the reusability and storage stability experiments revealed the economic value of the entire process by preserving around 95% and 83% of the initial catalase activity after the fifth and tenth operation cycles, respectively.