Extractive biocatalysis

Sometimes called extractive biocatalysis. It was also successfully applied to ketone reduction (a) Vicenzi, J.T., Zmijewski, M.)., Reinhard, M.R., Landen, B.E., Muth, W.L. and Marier, P.G. (1997) Enzyme and Microbial Technology, 20, 494-499. 

The effectiveness of liquid-liquid extractive biocatalysis was confirmed during the 1980s with a great deal of work directed towards solvent selection [60].Product recovery from the fermentation media using liquid-liquid extraction was already an established unit operation on the downstream processing of fermentation products [3]. The desirable organic solvent characteristics focused basically on its physicochemical properties. However, the use of organic solvents in an in situ recovery process also required low toxicity towards the biocatalyst (Table 2). 

To overcome the problem of product inhibition—extractive biocatalysis, use of supramolecular systems for forming inclusion complexes with the product, such as cyclodextrins and crown ethers, have been attempted. 

D Arrigo, P Fuganti, C., Pedrocchi Fantoni, G., and Servi, S. (1998) Extractive biocatalysis a powerful tool in selectivity control in yeast biotransformations. Tetrahedron, 54,15017-15026. 

III. EXTRACTIVE BIOCATALYSIS CONTROL OF SUBSTRATE AND PRODUCT CONCENTRATION BY ABSORBING RESINS... 

Biocatalysis Chemical reactions mediated by biological systems (microbial communities, whole organisms or cells, cell-free extracts, or purified enzymes aka catalytic proteins). 

However, the reactions were not enantioselective ones, though the most important aspect of the biocatalysis reaction should be in the enantioselective reaction. We and KragF independently reported the first enantioselective lipase-catalyzed reaction in February-March 2001. Since lipase was anchored by the IL solvent and remained in it after the extraction work-up of the product, we succeeded in demonstrating that recyclable use of the lipase in the [bmim][PFg] solvent system was possible (Fig. 2). ... 

The role of biocatalysis in two-phase systems has many parallels with the subject we have covered under extractive reactions. It appears that a two-phase system was originally considered for transformations of water insoluble substances like steroids. Now, a series of treatises are available which teach us that the maximum value of the apparent equilibrium constant for a second-order reaction in a two-phase system can exceed the equilibrium... 

The stirred batch reactors are easy to operate and their configurations avoid temperature and concentration gradient (Table 5). These reactors are useful for hydrolysis reactions proceeding very slowly. After the end of the batch reaction, separation of the powdered enzyme support and the product from the reaction mixture can be accomplished by a simple centrifugation and/or filtration. Roffler et al. [114] investigated two-phase biocatalysis and described stirred-tank reactor coupled to a settler for extraction of product with direct solvent addition. This basic experimental setup can lead to a rather stable emulsion that needs a long settling time. 

Biocatalysis. Biocatalysis, also termed biotransformation and bioconversion, makes use of natural or modified isolated enzymes, enzyme extracts, or whole-cell systems for the production of small molecules. A starting material is converted by the biocatalyst in the desired product. Enzymes are differentiated from chemical catalysts particularly with regard to stereoselectivity. 

The first company based upon applied biocatalysis also dates back to the 19 century. In 1874 Christian Hansen started a company in Copenhagen, Denmark. His company— named Christian Hansen s Laboratory to this day—was the first in the industrial market with a standardized enzyme preparation, rennet, for cheese making. Rennet, a mixture of chymosin (also called rennin) and pepsin, was and still is obtained by salt extraction of the fonrth stomach of suckling calves. 

Fig. 23.1 Microbial routes from natural raw materials to and between natural flavour compounds (solid arrows). Natural raw materials are depicted within the ellipse. Raw material fractions are derived from their natural sources by conventional means, such as extraction and hydrolysis (dotted arrows). De novo indicates flavour compounds which arise from microbial cultures by de novo biosynthesis (e.g. on glucose or other carbon sources) and not by biotransformation of an externally added precursor. It should be noted that there are many more flavour compounds accessible by biocatalysis using free enzymes which are not described in this chapter, especially flavour esters by esterification of natural alcohols (e.g. aliphatic or terpene alcohols) with natural acids by free lipases. For the sake of completeness, the C6 aldehydes are also shown although only the formation of the corresponding alcohols involves microbial cells as catalysts. The list of flavour compounds shown is not intended to be all-embracing but focuses on the examples discussed in this chapter... 

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. 

Biocatalysis covers a broad range of scientific and technical disciplines, which are geared to develop biocatalysts and biocatalytic processes for practical purposes. The natural pool of biocatalysts is extremely diverse and includes whole cells of microbial, plant or animal origin, as well as cell-free extracts and enz3rmes derived from these sources. The wide range of catalytic power offered by nature remains, however, largely imexplored. Currently, only a very small fraction of the known biocatalysts are actually being applied on a commercial scale. For example, of the approximately 4,000 known enzymes, about 400 are available commercially, but only about 40 are actually used for industrial applications. 

An example of integration of part of the downstream processing in the actual bioreactor is two-liquid-phase biocatalysis (see above), in which the organic-solvent phase is used as extractant for the product. The liquid-impelled loop reactor (Fig. 7.3) is specifically designed for this purpose. It is based on the well-known air-lift principle, but instead of air, a water-immiscible, heavier or lighter organic solvent is injected. 

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