Abstract
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.
Highlights
Enzymes have high catalytic activities and substrate specificities
Bhattacharya and Pletschke prepared magnetic xylanase-cross-linked enzyme aggregates (CLEAs) for bioconversion of sugarcane bagasse (SCB) to sugar [83]. They reported that the activity and stability of the magnetite-CLEAs and reusability of the CLEAs were enhanced; a higher hydrolysis yield was obtained from SCB. Immobilized enzymes retain their catalytic activity and are more robust to environmental changes compared with free enzymes
The operational stability depends on the immobilization method
Summary
Enzymes have high catalytic activities and substrate specificities. One single substrate is usually converted to one product. Enzyme immobilization is usually achieved by chemical covalent linking, affinity labeling, physical adsorption, or entrapment. These immobilization methods have been described in recent reviews [5,6,7,8]. Adsorption is a simple and low-cost method Enzyme immobilization by this method can provide high retention of enzymatic activity. Covalent linking methods involve chemical reactions between the side-chains in enzymes and surface-modified carrier materials. These methods do not require any modification of the target enzymes. Cross-linked enzyme aggregates (CLEAs) have recently been prepared for use in carrier-free enzyme-immobilization methods [2,4]. The use of CLEA reactors for chemical synthesis and environmental applications is introduced
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