An Investigation to Find the Effect of Bile Salts of on the Digestion of Lipids

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  • Topic: Enzyme, Lipase, Bile
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  • Published : October 30, 2008
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I have investigated that if there is an effect of bile salts on the digestion of lipids in the milk. When lipids are broken down in to fatty acids and glycerol (see below), the acid lowers the pH of the mixture. To help me determine and measure the digestion of lipids, a pH indicator phenolphthalein has been used to measure the pH of the mixtures. The pH indicator will change the colour from pink to either white (if bile is not contained) or brown (if bile is contained), this will indicate that the solution is changing from alkaline to acidic. So if I want to use phenolphthalein, I will have to firstly make the mixtures alkaline. This will be achieved by adding sodium carbonate to the milk until it is a strong alkaline which is just above pH 10. I used a universal indicator paper to find out if the pH is 10.

Lipids Fatty Acids + Glycerol

My null hypothesis is that bile salts have no effect on the digestion of lipid and lipase will still breakdown the fat, because the fat in the milk itself is probably already partly emulsified, the rate of reaction will be the same.

I drew a table, which showed different reagents in each tube and the time that took for the lipase to digest the lipids. The first 4 mixtures I created were controlled and were also not timed. They were used as colour standards which were maintained throughout the investigation. This was done to make it easier to determine the end point of the digestion of lipids.

In tube 1 and 2, bile was added to the mixture but no lipase was added. Phenolphthalein was not added to tube 2. These two tubes were produced to become colour standards when tube 5 and 7 are experimented. Tube 1 was produced as a colour standard to see how the solution should look like before the lipase is added. However, tube 2 was used to help me to judge the end point of the digestion of lipids.

On the other hand, tube 3 and 4 were added with lipase but no bile was added.. Phenolphthalein was not added in tube 4. Also in tube 3, the lipase was heated up to make it inactive. This when energy from heat break the bonds of the active site which changes the shape of the active site so the substrate is unable to bind with enzyme. As the lipase is inactive, it will not have any effect on the digestion so there will be no production of fatty acids to lower the pH of the solution as there is no change in the pH of the solution, there will be no change in the colour so the solution would stay pink due to the addition of phenolphthalein .Tube 4 does not contain phenolphthalein so it can act as the colour standard to determine the end point of tube 8 and 10. The time taken for the colour of the solution to change to the same colour as tube 4 will be measured. Bile was added to tube 5, 6 and 7 but bile was not added to tube 8, 9 and 10.

The effect of the addition of bile on the time taken for the digestion of lipid in milk

Treatment tube no.Presence of bileTime taken/ s

All the times are measured to 1/100th of a second but I have rounded up the numbers to the nearest second. This will make it easier for me when I calculate and if I kept it to 1/100th of a second, it would make my results more precise but I do not need to be that precise results in my experiment. While experimenting, when I noticed that the colour of the tube that I am experimenting on had become the same colour as the standard I produced earlier, I quickly stopped the timer and recorded the time. But the time between judging the colour and stopping the timer had changed my results to some extent, so experiment is not accurate. The tubes with bile are x and the tubes without bile is y

x = ∑x/n1
= 302/3
= 100.6* seconds

y = ∑y/n2
= 42/3
= 14 seconds
I will now work out the standard deviation of both the...
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