Enzymes in washing powders
Television commercials for washing powder often promote the "boosting power" of enzymes. Why are enzymes added to washing powder, and how do they work? Carry out some simple experiments to investigate this further.
What are enzymes?
Enzymes are biological molecules that catalyse (speed up) chemical reactions. Enzymes are specific—they will only work on particular molecules. For example, the enzyme sucrase will only bind with and break bonds in sucrose, not any other type of sugar.
Another characteristic of enzymes is that they can be re-used over and over again. A single enzyme will typically catalyse around 10,000 chemical reactions per second. This means that only a tiny amount of enzyme is needed to have a huge effect on a reaction.
The rate of enzyme activity depends on the amount of enzyme present, and also the temperature and pH of the reaction solution. The most favourable pH for many enzymes is 6-8, around neutral, but there are exceptions: pepsin, a digestive enzyme in the stomach, works best at pH 2.
Enzymes in washing powders
People have been experimenting with ways to use the power of enzymes to clean clothing for a long time; in fact, the first patent was in 1913.
Because stains are made of different types of molecules, a range of enzymes are needed to break them down. Proteases break down proteins, so are good for blood, egg, gravy, and other protein stains. Amylases break down starches, and lipases break down fats and grease. Washing powders usually only contain one type of enzyme, though some have two or all three.
Experiments to test the functionality of enzymes
A range of activities can be carried out in the classroom to demonstrate the power of enzymes as cleaning agents.
Designing a washing powder
Students can test the effectiveness of biological and non-biological detergents by observing the removal of images from exposed photographic film. Protease enzymes (alcalase and savinase) are added to enzyme-free washing powder to make up the ‘test powder’.
Hole in the jelly
This set of experiments suggests that students test a biological and ordinary washing powder on gelatine, agar, and egg yolk. Only a biological washing powder containing proteases should break down the gelatine and the egg yolk. The agar should not be dissolved by either washing powder because it is made of carbohydrates rather than proteins.
This experiment requires a spectrophotometer and casein protein coloured with blue dye. The aim is to compare the effectiveness of ordinary detergent (usually made specifically to get rid of oils) with a protease solution (to target the protein part of a stain). Students can plot a graph of colour intensity against time as a measure of the stain removal. A series of questions could be incorporated into a student worksheet.
Biological washing powders
This worksheet includes background information about enzymes in washing powder, questions about enzymes and their activity, and a final exercise requires students to plan an investigation.
The dirt on enzymes in detergents
This site provides a background of the use of enzymes in detergents, as well as a recipe for an enzyme detergent.
Sources of enzymes
The National Centre for Biotechnology Education at the University of Reading in the UK supplies a range of different digestive enzymes that can be used for experiments. The enzymes they use are: savinase and alcalase (both proteases), termamyl (amylase), lipolase (lipase), and celluzyme (cellulase).
You can get protease activity from natural products like kiwifruit and pineapple. We suggest that you crush the fruits in a buffer and then strain them to remove the fruit pulp. The filtered solution will contain a range of cellular molecules, including some proteases.
Another natural source of digestive enzymes is the pancreas, which can be collected from an abattoir and blended with buffer.
A note about enzyme units
The activity of enzymes is given as U/g (Units per gram), where the unit relates to a specific assay (measure of enzyme activity), e.g. one unit will liberate 1 mg of substrate per minute at pH7.0 at 25ºC.
Any enzyme solutions that are bought will have different levels of activity, and this should be taken account in a comparative experiment (i.e. make sure that the number of ‘units’ are comparable when testing different enzymes for their effectiveness).
The more crude the extract is, the lower the U/g measure.
- 15 November 2007