Enzyme is a biocatalyst which accelerates biological reactions. However, the concept of biocatalysts is very wide. It includes the pure enzyme, crude cell extract, viable plant cells, viable animal cells, viable microbial cells and intact non-viable microbial cells. Source of enzymes used in commerce is plant and animal cells. The sources of enzymes are microorganisms, higher plants and animals. Animal enzymes used currently are lipases, tripsin, rennets, etc. Most prevalent plant enzymes are papain, proteases, amylases and soybean lipoxygenase. These enzymes are used in food industries, for example, papain, extracted from papaya fruit is used as a meat tenderizer and pancreatic protease in leather softening and manufacture of detergents (Sasson, 1984).
In addition, microbial enzymes have gained much popularity. Production of primary and secondary metabolites by microorganisms is possible only due to involvement of various enzymes.
They are of two types: the extracellular and the intracellular enzymes. The former is secreted out the cell and the later remain within the cell. There is a wide range of extracellular enzymes produced by pathogenic and saprophytic microorganisms such as cellulase, polymethylgalacturonase, polyglacturonase, pectinmethylesterase, etc. These enzymes help in establishment in host tissues or decomposition of organic substrates. The intracellular enzymes such as invertase, uric oxidase, asparaginase are of high economic value and difficult to extract as they are produced inside the cell (Riviere, 1977). They can be obtained by breaking the cells by means of a homogenizer or a bead mill and extracting them through the biochemical processes. The process of enzyme purification is difficult as the cell debris and nucleic acid are not easily removed.
Microbial enzymes have two advantages over the animal and plant enzymes. Firstly, they are economical and can be produced on large scale within the limited space and time. The amount produced depends on size of fermenter, type of microbial strain and growth conditions. It can be easily extracted and purified. Secondly, there is technical advantages in producing enzymes via using microorganism as (i) they are capable of producing a wide variety of enzymes, (ii) they can grow in a wide range of environmental conditions, (iii) they show genetic flexibility that is why they can be genetically manipulated to increase the yield of enzymes, and (iv) they have short generation times (Trevan, 1987).
Enzyme containing detergents have been known since 1913 but their use was limited because of its instability in detergent formulations. In 1965, a new stable enzyme e.g. protease was introduced for application in detergent production. In 1970s, the first commercial process was used for production of fructose from glucose through the isomerization of glucose. Even in brewing industry, malt is used as the source of enzymes (Aunstrup et al, 1979).
Currentlt, more than 2,000 enzymes have been isolated and characterized, out of which about 1,000 enzymes are recommended for various applications. Among them about 50 microbial enzymes have industrial applications. Some of the enzymes are given in Table 17.1. In recent years, application of enzymes in industries has much significance. In 1981, the total world production of enzymes was estimated about 65,000 tonnes which valued about 4 x 108 U.S. dollars. During 1990s the cost may be expected to be doubled.