How does the amount of fat in milk affect the speed at which lipase works?

Anthony George

10TT

Biology Coursework

Lipase is an enzyme, which breaks down fat into fatty acids and glycerol. This diagram shows how you can use an indicator to show up the digestion of fats in milk.

Phenolphthalein is an indicator that turns pink in alkaline solutions of about pH 10. It will turn colourless in less alkaline solutions below pH 8.3. In this experiment the pink solution becomes colourless when digestion of fats produces enough acid to bring the pH below 8.3.

Plan

There are a few variables in this experiment; the enzyme works faster at body temperature, 37 Degrees Celsius, so if you changed the temperature of the experiment to body temperature, the whole experiment may work a lot faster. Another variation to this particular experiment would be to use different types of milk. Different milks have different fat contents so milk with a high fat content would take a long time to turn colourless whereas milk with a low fat content wouldn’t take that long to turn colourless because the lipase doesn’t have as much fat to break down.

To make sure the observations and measurements are as precise and as reliable as possible, and to make sure the experiment is a fair test, there are many precautions that need to be made. When timing the reaction in each of the experiments the stopwatch must be started when the lipase is added to each test tube. Also to see if each of the solutions are colourless the test tube should be held up against a sheet of white paper to give a reliable result that the solution is colourless and has no pink in it.

I predict that the ...

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I predict that the milk with the lowest fat content (Semi-Skimmed) will be the milk that takes longest to turn colourless and that the milk with the highest fat content (Single Cream) will take the least time to turn colourless. I think this because the more fat in the milk, the more fat is available to be turned into fatty acids, which turns the solution from pink to white as pH drops.

Observe

To make sure the results of this experiment were as accurate as possible, each milk was tested three times, and then an average was worked out.

Analyse

In conclusion the results tell me that my prediction was correct. Skimmed milk took 26.85 mins to become colourless because it had the lowest amount of fat in it, and Single Cream took 11.81 mins to become colourless because it had the highest amount of fat in it. This was what I thought in my prediction before I did the experiment.

Evaluate

Overall I think the procedure has worked well. The results were accurate and each experiment for the different milks followed the same plan and all the measurements were carefully carried out. I think the results can be trusted because each experiment was repeated three times to make sure the results were accurate. If I were to make any improvements I would use beakers instead of test tubes to do the experiments so that stirring would be easier. Another experiment I could do to find out more about lipase would be to the same experiment only not changing the milk, but changing the amount of lipase added or the temperature at which the experiment was done.