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.
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.
Some enzymes still extracted from animal and plant tissues. Enzymes such as papain, bromelain and ficin and other speciallity enzymes like lipoxygenase are derived from plants and enzymes pepsin and rennin are derived from animal. Most of the enzymes are produced by 日本保健品 microorganisms in submerged cultures in large reactors called fermentors. The enzyme production process can be divided into 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 the industrial applications must usually 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 high amount of the desired enzyme in a reasonable life time frame. Most of the industrially used microorganism 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.
Often enzymes do not have the desired properties for an industrial application. One option is find a better enzyme from nature. Another option is to engineer a commercially available enzyme to be a better industrial catalyst. 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.