An investigation to find the effect of bile salts on the digestion of fats.

AN INVESTIGATION TO FIND THE EFFECT OF BILE SALTS OF ON THE DIGESTION OF FATS

Proposed method

I intend to investigate the effect of bile salts on the digestion of fats. I will make up different concentrations of bile salts and add them to a lipase and fat (in this case full fat milk) mixture. I will then measure the digestion of fats by measuring the amount of fatty acids produced during the breakdown, which will be shown as a change in pH.

I predict the weaker the concentration of bile salts, the slower the digestion of fats, i.e. the pH change will occur slower.

Scientific background to the method

Bile is an important part of the digestion of fats. It is made in the liver, and is stored in the gall bladder. Bile contains bile salts, electrolytes, bilirubin, cholesterol, and phospholipids.1

The bile salts are mainly derived from Sodium glycocholate and sodium taurocholate. The Bile salts we are using in this investigation are synthesized sodium taurocholate. They do not work in exactly the same way as bile in our bodies, and so the effects on the digestion of fats in this investigation may be slightly slower than in real life.

Bile salts have detergent action on particles of fat, which causes them to break down or be emulsified into minute, microscopic droplets called micelles, which are only 0.5- 1.0 μm in diameter. (Fig. 1) These, however, are still not small enough to pass though the membranes, and need to be broken down further. This emulsification creates a greater surface area of fat on which the lipase can work. Effectively there is more substrate, and so all the lipase enzymes are working to their full capacity

(Fig. 1)

In the breakdown of fats, Fatty acids are produced, which changes the overall pH of the solution, giving a simple way of measuring the breakdown of fats.

fats → fatty acids + glycerol

→ +

Lipase is an enzyme that catalyses the reaction of the breakdown of fats. Using this enzyme, we are able to see the breakdown of fats in a short period of time, so it becomes easier to measure and analyse the end result.

The lipase we are using is pancreatic swine lipase because the gastric lipase has an optimum pH at neutrality compared to pancreatic lipase, whose optimum pH is more alkaline.2 The pancreatic lipase will work more effectively in the alkaline bile salts. The digestion of the fats will be quicker with the pancreatic lipase compared to the gastric lipase. This alkaline pH will also help us to see the fatty acids being formed, as there will be a greater difference in pH, helping us to see correlations.

The bile salts are alkaline providing alkaline conditions for the lipase to work in (optimum conditions) I expect that the more bile added, the more alkaline the conditions, therefore the optimum pH is reached. The pH in which an enzyme works is very important, and even slight changes in pH can affect the rate at which an enzyme works dramatically.

(Fig. 2)

The chyme (semi-digested food) is acidic when it leaves he stomach and enters the duodenum so the alkalinity of the bile salts helps neutralisation, so that the optimum pH of the lipase is reached. The acidic milk becomes neutralised by the alkaline bile salts, allowing the lipase to work faster because the optimum pH is reached. The initial pH of the solution has to be at the optimum pH for the enzyme to work because changes in pH change the amount of substrate converted. If the solution becomes ...