Biocatalysis defined

Bioaffinity chromatography, 6 399—400 Bioantimutagen, vanillin as, 25 556 Bioassay dyes, 9 518 Bioassays, microfluidics in, 26 968-969 Bioaugmentation, defined, 3 758t Bioaugmentation/bioremediation effluent treatment, 9 436, 438 Bioavailability, of antisense oligonucleotides, 17 628 Biocatalysis, 3 668-683 16 395. See also Biocatalyst entries... 

In this book, applied biocatalysis is defined as the application of a biocatalyst to achieve a desired conversion under controlled conditions in a bioreactor. This chapter focuses on the history of this field. 

Applied biocatalysis can be defined as the application of a biocatalyst to achieve a desired conversion under controlled conditiotts in a bioieactor. A biocatalyst can either be an enzyme, an enzyme complex, a cell organelle or a whole cell. The latter can be viable growing or non-growing or non-viable. Fttrihermoie, a biocatalyst can be free or immobihzed and this has far-reaching cortsequences, not only with respect to substrate supply and mass transfer in general, but sometimes also, in case of viable cells, with... 

In the context of this chapter biocatalysis is the use of enzymes or enzymes still associated with their parent cells, to carry out defined chemical reactions under controlled conditions, so as to efficiently convert raw materials into commercially more valuable products. Some of the commercial driving forces for the use of biocatalysts are listed in Table 13.1. 

Applied biocatalysis is older than written history. Ancient records, picturing the manufacture of foods and beverages, testily to the involvement of amylases and proteases from microbial, plant or animal origin, without the knowledge of those using them. These ancient applications can therefore be best described as an art and not as a technology or a scientifically defined method. 

The limits between the areas are blurred biotransformations and enzyme catalyses with cmde extracts or pure enzymes are often summarized under the term biocatalysis . Biocatalytic processes are taken to mean transformations of a defined substrate to a defined target product with one or several enzyme-catalyzed steps. 

The use of industrial enzymes for the synthesis of bulk and fine chemicals represents a somewhat specialized application for biocatalysts relative to their broader uses, as outlined above. Industrial biocatalysis is, however, becoming increasingly relevant within the chemical industry for the production of a wide range of materials (see Table 31.3).1,2,4-8 Broadly defined, a biocatalytic process involves the acceleration of a chemical reaction by a biologically derived catalyst. In practice, the biocatalysts concerned are invariably enzymes and are used in a variety of forms. These include whole cell preparations, crude protein extracts, enzyme mixtures, and highly purified enzymes, both soluble and immobilized. 

In biocatalysis /C2 is the rate measured when all enzyme molecules are complexed with reactant divided by the total concentration of enz)one present. This is the Turn-Over Number according to biochemists definition. Note that this differs from the Turn-Over Frequency as defined in heterogeneous catalysis where it is simply the rate normalised to the total number of surface sites present. In the latter case it is a function of the gas phase composition. 

An enzyme can be immobilized on/in a resin carrier either by adsorption (by hydrophobic, electrostatic or other forces) or it can be covalently linked to the resin. Carrier materials used for immobilization in biocatalysis include natural, synthetic, organic, inorganic, porous and non-porous materials. The main advantage compared to immobilization without a carrier is in general a better defined immobilized enzyme, as particle size, pore size, porosity, hydrophobicity and so on is pre-determined from the choice of carrier. However, the carrier cost is often significant. 

The reaction mixture for biocatalysis will be prepared by combining several components. To ensure defined water conditions in the final mixture, all these components should preferably be brought to known water activity beforehand. (It may be safe to disregard this for a component that has a limited affinity for water and makes up only a small proportion of the final mixture.)... 

Martinek et al. [28] defined the apparent reaction equilibrium in a biphasic system by the constant Kbi. In their model, the ratio K /K represents the equilibrium change when using a biphasic or pure aqueous medium. When the biocatalysis occurring in the aqueous phase involves four chemical species ... 

Mass transfer limitations can be relevant in heterogeneous biocatalysis. If the enzyme is immobilized in the surface or inside a solid matrix, external (EDR) or internal (IDR) diffusional restrictions may be significant and have to be considered for proper bioreactor design. As shown in Fig. 3.1, this effect can be conveniently incorporated into the model that describes enzyme reactor operation in terms of the effectiveness factor, defined as the ratio between the effective (or observed) and inherent (in the absence of diffusional restrictions) reaction rates. Expressions for the effectiveness factor (rj), in the case of EDR, and the global effectiveness factor (t ) for different particle geometries, in the case of IDR, were developed in sections 4.4.1 and 4.4.2 (see Eqs. 4.39-4.42,4.53,4.54,4.71 and 4.72). Such functions can be generically written as ... 

The basic principles of bioconversion, bioreactors and biocatalysis are introduced, together with a description of the most important biocatalyst immobilization techniques. The mass transfer phenomena involved in membrane systems are discussed along with some representative configurations of membrane bioreactors, whose behaviour can be described using a simple mathematical approach. For all the aforementioned systems the most significant parameters have been defined to estimate the system performance. 

In Part I a selection of the types of membrane reactor is presented, together with chapters on the integration of membrane reactors with current industrial processes. To summarize, in Chapter 1 (Calabro) membrane bioreactors are described from an engineering point of view, together with a straightforward description and simulation, with a simple mathematical approach, of the most important configurations and processes in which they are involved. Basic principles of bioconversion, bioreactors and biocatalysis with immobilized biocatalysts are also presented. For all the cited systems the most significant parameters are defined in order to estimate their performances. The best approaches for the preparation of... 

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