[ad_1]

Historical Background

Most of the reactions in living organisms are catalyzed by protein molecules called enzymes. Enzymes can rightly be called the catalytic machinery of living systems. The real break through of enzymes occurred with the introduction of microbial proteases into washing powders. The first commercial bacterial Bacillus protease was marketed in 1959 and major detergent manufactures started to use it around 1965. The industrial enzyme producers sell enzymes for a wide variety of applications. The estimated value of world market is presently about US$ 2 billion. Detergents (37%), textiles (12%), starch (11%), baking (8%) and animal feed (6%) are the main industries, which use about 75% of industrially produced enzymes.

Enzyme Classification

Presently more than 3000 different enzymes have been isolated and classified. The enzymes are classified into six major categories based on the nature of the chemical reaction they catalyze:

1. Oxidoreductases: catalyze oxidation or reduction of their substrates.
2. Transferases: catalyze group transfer.
3. Hydrolases: catalyze bond breakage with the addition of water.
4. Lyases: remove groups from their substrates.
5. Isomerases: catalyze intramolecular rearrangements.
6. Ligases: catalyze the joining of two molecules at the expense of chemical energy.

Only a limited number of all the known enzymes are commercially available. More than 75% of industrial enzymes are hydrolases. Protein-degrading enzymes constitute about 40% of all enzyme sales. More than fifty commercial industrial enzymes are available and their number is increasing steadily.

Enzyme Production

Some enzymes are still extracted from animal and plant tissues. Enzymes such as papain, bromelain, and ficin, and other specialty enzymes like lipoxygenase are derived from plants, and enzymes pepsin and rennin are derived from animals. Most of the enzymes are produced by microorganisms in submerged cultures in large reactors called fermentors. The enzyme production process can be divided into the following phases:

1. Selection of an enzyme.
2. Selection of production strain.
3. Construction of an overproducing stain by genetic engineering.
4. Optimization of culture medium and production condition.
5. Optimization of recovery process.
6. Formulation of a stable enzyme product.

Criteria used in the selection of an industrial enzyme include specificity, reaction rate, pH and temperature optima and stability, effect of inhibitors, and affinity to substrates. Enzymes used in industrial applications must usually be tolerant against various heavy metals and have no need for cofactors.

Microbial Production Strains

In choosing the production strain, several aspects have to be considered. Ideally, the enzyme is secreted from the cell. Secondly, the production host should have a GRAS-status. Thirdly, the organism should be able to produce a high amount of the desired enzyme in a reasonable lifetime frame. Most of the industrially used microorganisms have been genetically modified to overproduce the desired activity and not to produce undesired side activities.

Enzyme Production by Microbial Fermentation

Once the biological production organism has been genetically engineered to overproduce the desired products, a production process has to be developed. The optimization of a fermentation process includes media composition, cultivation type, and process conditions. The large volume industrial enzymes are produced in 50-500 m3 fermentors. The extracellular enzymes are often recovered after cell removal (by vacuum drum filtration, separators, or microfiltration) by ultrafiltration.

Protein Engineering

Often enzymes do not have the desired properties for an industrial application. One option is to find a better enzyme from nature. Another option is to engineer a commercially available enzyme to be a better industrial catalyst. Two different methods are presently available: a random method called directed evaluation and a protein engineering method called rational design.

Enzyme Technology

This field deals with how enzymes are used and applied in practical processes. The simplest way to use enzymes is to add them into a process stream where they catalyze the desired reaction and are gradually inactivated during the process. This happens in many bulk enzyme applications and the price of the enzymes must be low to make their use economical. An alternative way to use enzymes is to immobilize them so that they can be reused. Enzymes can be immobilized by using ultrafiltration membranes in the reactor system. The large enzyme molecule cannot pass through the membrane but the small molecular reaction products can. Many different laboratory methods for enzyme immobilization based on chemical reaction, entrapment, specific binding, or absorption have been developed.

Large Scale Enzyme Applications

1. Detergents: Bacterial proteinases are still the most important detergent enzymes. Lipases decompose fats into more water-soluble compounds. Amylases are used in detergents to remove starch-based stains.
2. Starch Hydrolysis and Fructose Production: The use of starch-degrading enzymes was the first large-scale application of microbial enzymes in the food industry. Mainly two enzymes carry out the conversion of starch to glucose: alpha-amylase and fungal enzymes. Fructose is produced from sucrose as a starting material.
3. Drinks: Enzymes have many applications in the drink industry. Lactase splits milk-sugar lactose into glucose and galactose. Addition of pectinase, xylanase, and cellulase improves the liberation of juice from pulp. Similarly, enzymes are widely used in wine production.
4. Textiles: The use of enzymes in the textile industry is one of the most rapidly growing fields in industrial enzymology. The enzymes used in the textile field are amylases, catalase, and lactases which are used to remove starch, degrade excess hydrogen peroxide, bleach textiles, and degrade lignin.
5. Animal Feed: Addition of xylanase to wheat-based broiler feed has increased the available metabolizable energy 7-10% in various studies. Enzyme addition reduces viscosity, which increases absorption of nutrients, liberates nutrients either by hydrolysis of non-degradable fibers or by liberating nutrients blocked by these fibers, and reduces the amount of feces.
6. Baking: Alpha-amylases have been most widely studied in connection with improved bread quality and increased shelf life. Use of xylanases decreases the water absorption and thus reduces the amount of added water needed in baking. This leads to more stable dough.
7. Pulp and Paper: The major application is the use of xylanases in pulp bleaching. This reduces considerably the need for chlorine-based bleaching chemicals. In paper making, amylase enzymes are used especially in modification of starch. Pitch is a sticky substance present mainly in softwoods. Pitch causes problems in paper machines and can be removed by lipases.
8. Leather: Leather industry uses proteolytic and lipolytic enzymes in leather processing. Enzymes are used to remove unwanted parts. Bacterial and fungal enzymes are used to make the leather soft and easier to dye.
9. Specialty Enzymes: There are a large number of specialty applications for enzymes, including use of enzymes in analytical applications, flavor production, protein modification, and personal care products, DNA-technology, and fine chemical production.
10. Enzymes in Analytics: Enzymes are widely used in the clinical analytical methodology. Contrary to bulk industrial enzymes, these enzymes need to be free from side activities. An important development in analytical chemistry is biosensors.
11. Enzymes in Personal Care Products: Personal care products are a relatively new area for enzymes. Enzyme solutions are used for contact lens cleaning and removal of residual hydrogen peroxide after disinfection. Enzymes are also studied for applications in skin and hair care products.
12. Enzymes in DNA-Technology: DNA-technology is an important tool in the enzyme industry. Enzymes are crucial tools in the reading and modification of genetic language.
13. Enzymes in Fine Chemical Production: Commercial production of chemicals by living cells using pathway engineering is still a developing field.

[ad_2]

Ihab Salloum