CHAPTER 14: Cross-linked Enzyme Aggregates (CLEAs): From Concept to Industrial Biocatalyst

Biocatalysis is green and sustainable, offering many environmental and economic benefits in a variety of industrial settings. However, some applications of enzymes are hampered by a lack of long-term operational stability and difficult recovery and re-use of the enzyme. Enzymes are soluble in water and are often used on a single-use, throw-away basis. Such applications of enzymes can be rendered more cost-effective by immobilising the enzyme as an insoluble powder that can be easily recovered and recycled. This can be achieved by immobilisation on a prefabricated carrier, in a polymer matrix or by forming carrier-free, cross-linked enzyme aggregates (CLEAs). An important processing advantage of CLEAs over carrier-bound enzymes is their much higher catalyst and volumetric productivities. Furthermore, they can be produced directly from crude cell lysate, exhibit enhanced operational and storage stability and are easily recycled and reused. Their scope and cost-effectiveness has been further enhanced by the development of combi-CLEAs, containing two or more enzymes, and magnetic CLEAs. The latter are readily separated at industrial scale using existing magnetic separation equipment and are particularly advantageous in applications where separation of the catalyst from mixtures containing suspended solids is required, e.g. in first- and second-generation biofuels production.