Sensors: pH Loggers: Any EASYSENSE Logging time: EasyLog

L3 Biology 77 - 1(V2)

Biology

77 The effect of lipase on milk This investigation measures the change in pH in a sample of milk that is being digested by Lipase.

Milk contains a variety of fats (lipids); the lipase digests the fats (breaks the fats down into smaller molecules). One of the products of the digestion is acidic; the increase in acidity is therefore related to the digestion of fatty materials in the milk sample.

What you need 1. An EASYSENSE logger

2. A Smart Q pH sensor

3. A Smart Q reaction switch (optional)

4. Lipase enzyme*

5. Selection of milks (skimmed, semi skimmed, jersey, full fat, etc.)

6. Beaker to act as a water bath for the experiment (250 or 500 ml capacity)

7. Boiling tube for the reaction

8. 1 ml capacity syringe or Pasteur pipette.

What you need to do Note: As with all enzyme based reactions and investigations you must take extra care to not let anything that has come into contact with enzyme come into contact with the substrate. That is, anything that has come into contact with the lipase should not come into contact with the milk (substrate).

1. You will need to use the large beaker as a water bath. The pH sensor simply rests inside the boiling tube and reaction mixture; there should be no need to support the electrode.

2. Measure 25 cm3 of milk into the boiling tube. Place the boiling tube into a beaker of warm water (water bath) and leave for about 3 minutes to reach the temperature of the water bath.

3. Pour about 3cm3 of Lipase into a small beaker or test tube. Use a pipette to draw up 1cm3 of the lipase and leave ready for use.

4. Place the pH electrode into the milk.

5. Select EasyLog from the Home screen.

6. Click on Start and immediately add the Lipase (ideally the adding and starting should be at the exact same time).

If you have a Reaction switch connected, press the button just as the lipase is added to mark the graph to show the start of the reaction.

7. Allow the reaction to continue until the rate of change of pH has slowed significantly (this will be about 10 minutes).

8. Stop the recording and display the detail of the graph by right clicking in the graph area and selecting Autoscale.

To compare different milk samples.

1. Dispose of the sample of milk that has been treated with lipase; wash the boiling tube and the pH electrode to remove the milk residues.

2. After step 8, select Overlay and prepare a new sample of milk and enzyme as described (for comparison the only thing that should change in the experiment is the type of milk being tested).

3. Add the lipase; the recording will last for as long as the first recording was allowed to run.

4. Use Save As to save the data, use a new name to keep the data from previous runs safe.

5. Label the graph line using the Add Text tool (right click graph menu).

6. Repeat for as many milk samples as you can.

Results You will record a graph that looks something like the example below. This was of a milk sample and lipase at two different temperatures. Note how the lines do not show much detail immediately after the collection of data.

Use Autoscale or Sensor settings (Options) to adjust the scale to reveal the detail of the recording.

L3 Biology 77 - 2(V2)

Questions 1. Describe the shape of the graph.

2. Explain the shape of the graph. For example, why is it not a straight line?

3. What do you notice about the rate of change of pH over the first 1 to 2 minutes?

4. If you have access to data for different milk types, compare the rate of change and the amount of change using the values and difference tools.

5. When lipase digests the fats in milk it produces what products?

6. What changes the pH of the milk when lipase is added to it?

7. Why would the rate of change of pH and the amount of change of pH be of use to a dairy farmer or a purchaser of milk from a farmer?

L3 Biology 77 - 3(V2)