Enzymes are protein molecules that speed up chemical reactions by helping to break other target molecules into smaller pieces. Enzymes provide enhanced cleaning performance by breaking down specific kinds of soils like proteins and starches that will not occur under normal conditions and help the breakdown to proceed at a greatly accelerated rate. 

Protein stains from sources such as milk, cocoa, blood, egg yolk, and grass are just as resistant to removal from fibers by simple detergents as are bleachable stains, particularly after the stains have dried. However, proteolytic (protein cleaving) enzymes also called proteases are usually capable of eliminating such soil without difficulty during the course of cleaning.

Working environment  

The working environment of an enzyme is very important to its functioning. Most have very specific requirements for temperature (Figure 1) and pH (Figure 2). The maximum activity of the enzyme is in a narrow range and falls off rapidly outside this range.

All enzymes require water and are water-soluble. This is probably where analogies to living organism creep in. Enzymes for example, are said to be "killed off" by extremes of heat or acidity /alkalinity, in a way bacteria may be killed. However this is not the case and the enzyme is often only deactivated when encountering an environment outside the normal working range. When conditions are brought back within the range enzyme activity can recommence, however, there are means of permanently disabling enzymes.

Enzyme types

Living cells, notably yeast, molds, bacteria, and actinomycetes, generate enzymes. The commercially available enzymes fall into three basic categories:

1) made from animals
2) made from plants
3) microbially derived preparations

All enzymes are specific for a particular application, as each type can breakdown a particular type of stain. Enzymes can be classified according to their action, the important classes of which are listed below:

· Proteases, which breakdown proteins such as blood, egg, milk, and grass.
· Amylases, which breakdown starch-based stains, such as gravy, pudding, and potato.
· Lipases, which breakdown grease, oils and fats such as margarine and oil.
· Cellulases, which breakdown cellulosic materials and are used for color maintenance or restoration benefits on cotton textiles.

Enzymes work best under mild conditions, temperature of 100-140º F and a pH range of 4-8, although some enzymes have been developed that can perform under more extreme conditions. 

How enzymes work

Most of the reactions in which compounds are broken down need some energy to get them started. Enzymes make it possible for reactions to occur with much less energy.

Enzymes are biological catalysts. They not only increase the rate of a biochemical reaction exponentially but they are highly specific. An enzyme is typically a large protein molecule that contains one or more active sites where interactions with substrates (the target molecule on which the enzyme action takes place, it could be a protein, starch, or grease) take place. They work the same way as a particular key fits a particular lock.

An enzyme can be pictured as a large, irregularly shaped molecule with a cleft or crevice in its middle. Inside the crevice is an active site (Figure 3a), a small region with the shape and chemical composition necessary to bind and hold the substrate (Figure 3b). The holding action weakens (Figure 3c) and breaks down the intramolecular bonds (bonds that hold the substrate together), splitting it into smaller fragments (Figure 3d). In other words, the active site acts like a lock into which only a specific key can fit and opens the locking mechanism, and this process is in most cases extremely fast and efficient.

Stability

In addition to stability at higher temperatures and pH values, the enzyme should be compatible with other ingredients, such as surfactants, sequestering agents, perfumes and other builders.

Only above a certain temperature does the stability of the enzyme decrease, and then very rapidly, leading to decomposition in a very short time. Other modes of decomposition can also cause problems. Some of them can be addressed, for instance, detergents containing enzymes if they are properly formulated, the proteases currently available are not subject to significant decomposition by atmospheric oxygen either during storage or in  use.  

Stability problems with respect to anionic surfactants and oxidizers were once subject of debate, but usually are readily solved by the proper choice of proteases and the appropriate formulation. Since amylases and lipases are made up of proteins, great care should be taken when blending these proteins with certain strains of proteases, as the protease can attack both these enzyme types, also the pH can reduce the stability of enzymes.

Aziz Ullah, Ph.D., MBA is president of Fabpro Manufacturing, is a leading formulator of high-quality carpet and upholstery cleaning products. He is a member of the American Chemical Society, senior member of the American Association of Textile Chemists and Colorists, member of The Textile Institute (UK), and formulator of Butler Maximum Products. He can be reached at www.fabpro.com.

From the March 2002 edition of Cleanfax magazine. For a free introductory subscription, click here.