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How can a washing power enzyme be used to remove stains most efficiently?
How can a washing power enzyme be used to remove stains most efficiently?
Measuring enzyme activity
The activity of most enzyme in reactions is measured according to the rate of substrate decomposition or product formation.
Type of reaction and data collection method
Gas reaction
Counting bubbles formed
Rise of enzyme-soaked disc in substrate solution
Displacement of syringe cap with increasing volume
Pressure change in sealed environment
Digestion of a solid
Calculate percentage mass change
Measure the change in diameter using substrate infused agar cubes
Measure the volume of liquid produced
Digestion of a liquid
Diffusion out of a dialysis tube or passage (if the product is permeable but the substrate is not)
Colour change
Using a spectrophotometer or colorimeter
The substrate and enzyme solution can be mixed with another solution that is known to change colour in the presence of the substrate. When there is no colour change seen, all of the substrate has reacted.
Factors that affect enzyme activity (Independent variable)
Temperature
At low temperatures, enzyme activity is low as enzymes and substrates have less kinetic energy and are less likely to collide. Raising the temperature increases the kinetic energy, the rate of collision, and enzyme activity. Despite this, enzyme activity is optimised at around 40˚C as higher temperatures cause enzymes to denature. Hence, temperature is an appropriate and measurable independent variable as it will affect enzyme activity.
While changing the temperature is easy, maintaining it over time is difficult and will be necessary within trial groups for accurate results. This limitation can be overcome by keeping the sample in a water bath or on a cooling/heating plate set at a certain temperature.
pH level
Changes in pH may cause enzymes and substrates to denature so that substrates cannot bind to the active site or be catalysed. pH level can be changed easily by adding pH buffers to the enzyme or substrate solution, which are found in most laboratories. They can also be made by mixing a weak acid and its conjugate base before adding a strong acid or base to acheive the desired pH level, which can be tested using universal litmus paper. Hence, pH level is a feasible and appropriate and measurable independent variable as it will affect enzyme activity.
Safety and risk assessment is important if the pH level is changed as concentrated acidic solutions are strongly corrosive to all body tissue, especially the eyes and skin. Adding an acid to the stain on the clothing may corrode it. Hence, changing pH has major limitations.
Substrate concentration
Increasing the substrate concentration increases the rate of reaction as the rate of collision between substrate molecules and enzymes will be higher, so more product will be formed. The findings of an investigation could provide the optimal ratio of enzyme to substrate to minimise excessive washing power use.
No limitations can be seen
Presence of inhibitors
Inhibitors are molecules that bind to a specific enzyme, which either stop a substrate from entering the enzyme's active site and/or hinder the enzyme from catalysing the reaction. Given this, more inhibitors will decrease the amount of products formed. Hence, the concentration of inhibitors can be changed to evaluate its effect on enzyme activity.
No limitations can be seen.
Common enzyme-catalysed reactions in washing powders
Amylase + starch = maltose
Amylase is found in saliva. Sources of starch include: cereals and root vegetables.
To measure enzyme activity, the enzyme and substrate solution can be placed in iodine as it will change colour if starch is present.
To precisely determine when the reaction stops, the enzyme-substrate solution needs to be tested every few seconds, which may not be feasible due to insufficient equipment. Given this, a test could be done to determine an approximate range of time when the reaction stops so that the solution can be tested more often during this time.
Amylase inhibitors are found in the seeds of plants, such as cereal grains and legumes.
The optimum pH level is 6.7–7.0.
Protease + protein = amino acids
Protease can be bought as a supplement and proteins are found in eggs, blood, milk, and gravy.
Stomach protease (pepsin) works best in acidic environments with a pH of 1.5 - 2.0 while pancreatic protease (trypsin) works best in neutral environments with a pH of 7.5 - 8.0. The pH environment of a stain will usually be neutral or basic. It should not be acidic otherwise the clothing may corrode. Hence, pepsin should not be used.
Protease inhibitors include saquinavir and ritonavir.
Lipase + fat = fatty acids + glycerol
Lipase can be bought in supplement form or found naturally in avocados. There are high levels of fat in olive oil and milk.
The reaction can be measuring using phenolphthalein, an indicator that is pink in alkaline solutions of about pH10. When the pH drops below pH 8.3, phenolphthalein goes colourless. When fat is broken down to form fatty acids and glycerol, the pH is reduced to below 8.3 and the phenolphthalein turns colourless. In light of this, pH cannot be changed if this enzyme-catalysed reaction is tested.
Enzymes
Enzymes acts as catalysts for chemical reactions, signifcantly lowering the activation energy for a substrate to react without being consumed. Hence, in an enzyme-catalysed reaction, the initial number of enzymes present should be the same as the final number of enzymes.
How they increase the efficiency of washing powers to remove stains
Stains may be composed of fats or proteins, which are not removable by detergent alone. Catabolic enzymes are needed to do break down the stain. For example, lipase breaks down fat stains into fatty acids and gylcerol, amalyse breaks down starch stains into maltose, and protease breaks down a protein stain into amino acids. As these products are water soluble, they can be washed away.
Biological washing powders can be used to test enzyme efficiency in this experiment as they contain certain enzymes that are very effective at cleaning stains.
Controlled variables
Factors that may not be controlled
Concentration of enzymes in biological washing power
Concentration of substrates
Factors that are controlled
Type of fabric
Temperature
Amount of enzymes
Amount of substrates used to create the stain
pH level
Size of the stain
