4. Enzymes as Industrial Catalysts

4.1. Industrial Biocatalysts

Enzymes make it possible to replace well-known and estabilished processes with better-controlled processes having:

• fewer byproducts
• lower energy consumption
• less environmental pollution
• and even enhanced nutritional value of natural substances.

Characteristics of Industrial Biocatalysts

"Biocatalyst" is a broad term used for an industrial catalyst produced biologically. This term is used synonymously for:

• pure enzymes
• enzyme mixtures
• formulated enzyme products
• crude enzymes
• cell fragments
• and whole cells (viable or non-viable).

In a few cases plants or animals are used for the isolation of enzymes, but industrial enzymes are produced predominantly by microorganisms in large fermentor vessels.

By mutation and selection techniques the production of the enzyme of choice can be increased to high levels.

Often the microorganism excrete the desired enzyme into the liquid medium in which they grow. The isolation is easy and large amounts of enzyme can then be obtained in a relatively short time and at low cost.

The development of a commercial production process for an enzyme, based on fermentation, requires a significant effort in research and development.

Industrial enzymes are not sold as 100% pure powder. For ease of handling, stability and accordingly to the market applications, special formulations are developed.

Catalysis by enzymes offers a number of advantages over traditional chemical catalysis as enzymes:

• have a high catalytic power
• work under mild conditions of temperature, pH and pressure
• display high specificity for the substrate (they frequently distinguish between closely related molecules
• some enzymes can perform well in organic solvents (provided these are chosen properly).

• they may be insufficiently stable for commercial applications
• separation of the enzyme from the aqueous reaction mixture for subsequent reuse is often difficult.
• recovery of the product (usually present in low concentrations in the aqueous solution) is also difficult.

The reduction or elimination of these problems is the goal of much current research.

Part (or all) of the water content can be replaced by a suitable organic solvent in order to overcome eventual difficulties associated with the use of water-soluble enzymes in aqueous solutions (e.g., low solubilities of substrates or products, inhibition of the enzimatic reaction, etc).

It is possible the immobilization of the enzymes, thus converting them into insoluble forms.

Choice of the Industrial Biocatalyst

• Catalyst development and performance costs.
• Technical aspects of the production process and end-product characteristics. If product purity (no by-product) is important or if stereoselectivity is required enzymes can be advantageous.
• External factors - legal aspects, safety criteria, specific consumer demands (such as a preference for "natural" products).