Uniform cross-linked cellulase aggregates prepared in millifluidic reactors

Enzyme immobilization technology as a tool to innovate in the production of biofuels: A special review of the Cross-Linked Enzyme Aggregates (CLEAs) strategy

This review emphasizes the crucial role of enzyme immobilization technology in advancing the production of two main biofuels, ethanol and biodiesel, with a specific focus on the Cross-linked Enzyme Aggregates (CLEAs) strategy. This method of immobilization has gained attention due to its simplicity and affordability, as it does not initially require a solid support. CLEAs synthesis protocol includes two steps: enzyme precipitation and cross-linking of aggregates using bifunctional agents. We conducted a thorough search for papers detailing the synthesis of CLEAs utilizing amylases, cellulases, and hemicellulases. These key enzymes are involved in breaking down starch or lignocellulosic materials to produce ethanol, both in first and second-generation processes. CLEAs of lipases were included as these enzymes play a crucial role in the enzymatic process of biodiesel production. However, when dealing with large or diverse substrates such as lignocellulosic materials for ethanol production and oils/fats for biodiesel production, the use of individual enzymes may not be the most efficient method. Instead, a system that utilizes a blend of enzymes may prove to be more effective. To innovate in the production of biofuels (ethanol and biodiesel), enzyme co-immobilization using different enzyme species to produce Combi-CLEAs is a promising trend.

(Magnetic) Cross-Linked Enzyme Aggregates of Cellulase from T. reesei: A Stable and Efficient Biocatalyst

Cross-linked enzyme aggregates (CLEAs) represent an effective tool for carrier-free immobilization of enzymes. The present study promotes a successful application of functionalized magnetic nanoparticles (MNPs) for stabilization of cellulase CLEAs. Catalytically active CLEAs and magnetic cross-linked enzyme aggregates (mCLEAs) of cellulase from Trichoderma reesei were prepared using glutaraldehyde (GA) as a cross-linking agent and the catalytic activity and stability of the CLEAs/mCLEAs were investigated. The influence of precipitation agents, cross-linker concentration, concentration of enzyme, addition of bovine serum albumin (BSA), and addition of sodium cyanoborohydride (NaBH₃CN) on expressed activity and immobilization yield of CLEAs/mCLEAs was studied. Particularly, reducing the unsaturated Schiff's base to form irreversible linkages is important and improved the activity of CLEAs (86%) and mCLEAs (91%). For increased applicability of CLEAs/mCLEAs, we enhanced the activity and stability at mild biochemical process conditions. The reusability after 10 cycles of both CLEAs and mCLEAs was investigated, which retained 72% and 65% of the initial activity, respectively. The thermal stability of CLEAs and mCLEAs in comparison with the non-immobilized enzyme was obtained at 30 °C (145.65% and 188.7%, respectively) and 50 °C (185.1% and 141.4%, respectively). Kinetic parameters were determined for CLEAs and mCLEAs, and the K_M constant was found at 0.055 ± 0.0102 mM and 0.037 ± 0.0012 mM, respectively. The maximum velocity rate (V_max) was calculated as 1.12 ± 0.0012 µmol/min for CLEA and 1.17 ± 0.0023 µmol/min for mCLEA. Structural characterization was studied using XRD, SEM, and FT-IR. Catalytical properties of immobilized enzyme were improved with the addition of reducent NaBH₃CN by enhancing the activity of CLEAs and with addition of functionalized aminosilane MNPs by enhancing the activity of mCLEAs.

Enzymatic pretreatment of algal biomass has different optimal conditions for biogas and bioethanol routes

Enzymatic pretreatment is emerging as an efficient tool for the extraction of biofuel precursors from algal biomass. However, yardsticks for end-use directed selection of optimal pretreatment conditions are not yet identified. The present study, for the first time, reveals different optimal conditions for algal biomass solubilization and sugar release. Algal biomass pretreatment optimization was carried out using the Taguchi method. Crude enzyme from Aspergillus fischeri was found effective for pretreatment of Chlorella pyrenoidosa. Maximum sugar yield (190 mg g^-1 biomass) from algal biomass was observed at a substrate concentration of 4 g L^-1, with a 5% enzyme load at temperature 60°C, pH 5.5, and shaking speed of 80 rpm. In contrast, maximum sCOD (1350 mg g^-1 biomass) was obtained at 2 g L^-1 substrate concentration with enzyme load of 20% v/v, at 60°C, pH 4, and shaking speed of 100 rpm. Hence, the first set of conditions would be more beneficial for bioethanol production. Whereas another set of conditions would improve the biofuel production that requires maximum solubilization of algal biomass, such as fermentative methane production. Overall, the present observations established that process conditions required for enzymatic pretreatment of algal biomass should be selected according to the desired biofuel type.

A Millifluidic Device with Embedded Cross-Linked Enzyme Aggregates for Degradation of H2O2

Millifluidic devices decorated with enzymes have been used for enzymatic reactions in continuous processes, but low enzymatic activity and enzyme leaching remain as challenges. Herein, we develop a strategy to embed cross-linked enzyme aggregates (CLEAs) on the surfaces of millifluidic devices to achieve higher enzymatic activity and better stability. Catalase was chosen as a model enzyme to degrade H₂O₂ in wastewater samples. First, CLEA of catalase (153 ± 10 nm) was formed by simultaneous precipitation and cross-linking with 25.0 wt % acetonitrile containing 0.025 wt % glutaraldehyde in a millifluidic device. To immobilize CLEA, we first swell a piece of plastic tubing by using 5.0 wt % acetonitrile and then immerse it in an aqueous solution with 5.0 wt % (3-aminopropyl)triethoxysilane (APTES) and 5.0 wt % dextran polyaldehyde (DPA) subsequently. After CLEA is absorbed inside the expanded polymer network of the tubing, the tubing is tightened by using a vacuum to secure the immobilized CLEA. The millifluidic device decorated with CLEA of catalase has total activity of 660 U for degradation of H₂O₂, and it shows good stability under a flow rate of 200 μL/min. The tubing can be used to degrade 0.1 wt % H₂O₂ solution continuously for 3 h or remove 2 wt % residual H₂O₂ in wastewater for 2 h. The technique is general enough and can be applied to other types of enzymes for continuous enzymatic reactions.

Techniques for Preparation of Cross-Linked Enzyme Aggregates and Their Applications in Bioconversions

Enzymes are biocatalysts. They are useful in environmentally friendly production processes and have high potential for industrial applications. However, because of problems with operational stability, cost, and catalytic efficiency, many enzymatic processes have limited applications. The use of cross-linked enzyme aggregates (CLEAs) has been introduced as an effective carrier-free immobilization method. This immobilization method is attractive because it is simple and robust, and unpurified enzymes can be used. Coimmobilization of different enzymes can be achieved. CLEAs generally show high catalytic activities, good storage and operational stabilities, and good reusability. In this review, we summarize techniques for the preparation of CLEAs for use as biocatalysts. Some important applications of these techniques in chemical synthesis and environmental applications are also included. CLEAs provide feasible and efficient techniques for improving the properties of immobilized enzymes for use in industrial applications.

Recycle of Immobilized Endocellulases in Different Conditions for Cellulose Hydrolysis

The immobilization of cellulases could be an economical alternative for cost reduction of enzyme application. The derivatives obtained in the immobilization derivatives were evaluated in recycles of paper filter hydrolysis. The immobilization process showed that the enzyme recycles were influenced by the shape (drop or sheet) and type of the mixture. The enzyme was recycled 28 times for sheets E' and 13 times for drops B'. The derivative E' showed the highest stability in the recycle obtaining 0.05 FPU/g, RA of 10%, and FPU Yield of 1.64 times, higher than FPU spent or Net FPU Yield of 5.3 times, saving more active enzymes. The derivative B showed stability in recycles reaching 0.15 FPU/g of derivative, yield of Recovered Activity (RA) of 25%, and FPU Yield of 1.57 times, higher than FPU spent on immobilization or Net PFU Yield of 2.81 times. The latex increased stability and resistance of the drops but did not improve the FPU/gram of derivative.

Hollow cross-linked enzyme aggregates (h-CLEA) of laccase with high uniformity and activity

Hollow cross-linked enzyme aggregates of laccase (h-CLEA laccase) can be prepared by employing a millifluidic reactor carrying two coaxial laminar flows. In a confluence zone where acetonitrile and an aqueous solution of laccase meet, diffusion of acetonitrile into the aqueous solution gives rise to rapid precipitation of laccase aggregates at the water/acetonitrile interface, as is evidenced by fluorescence images. By controlling the flow rates carefully in the laminar flow regions, h-CLEA laccase around 220±10nm can be obtained, and the size of the h-CLEA laccase increases with increasing flow rates of both solutions. The h-CLEA laccase particles are distinctly different from CLEA laccase prepared in batch processes. The former only consist a crust of cross-linked enzymes (with a hollow core) whereas the latter has a highly porous structure. When the h-CLEA laccase is used as biocatalysts, their activity (0.26U/mg) is comparable to that of free enzymes at neutral pH due to the hollow structure. Moreover, the activity of h-CLEA laccase is higher than that of free laccase at high pH. For example, trypan blue (a dye molecule) can be decolorized completely in the presence of h-CLEA laccase within 270min even at pH 10.0, at which the free enzyme completely loses its activity. Because of their uniform sizes, h-CLEA laccase can be trapped in a membrane for continuous degradation of trypan blue up to 96h without losing any activity. This study shows the superiority of h-CLEA laccase compared to other types of immobilized enzymes.

Carrier-free co-immobilization of xylanase, cellulase and β-1,3-glucanase as combined cross-linked enzyme aggregates (combi-CLEAs) for one-pot saccharification of sugarcane bagasse

Combined cross-linked enzyme aggregates (combi-CLEAs) of xylanase, cellulase and β-1,3-glucanase.