Digestion of Fat

Via the oesophagus, the food that was broken down in the mouth is transported to the stomach. There, the fat is extracted mechanically from the food for the most part. It is not very miscible with the aqueous gastric fluid, so the fat molecules assemble into big droplets. The fats have to be physically and chemically altered before they can pass the intestinal wall and be absorbed by the body. Already within the first three centimetres of the small intestine two essential helpers of the fat digestion are added: the gallic acid from the gall bladder and the pancreas lipase from the pancreas. The gallic acid is responsible for the physical part of the digestion of fat. It splits up the big droplets into small fat droplets. The pancreatic enzyme disperses these droplets and in this way free fatty acids and monoglycerides are generated. These building blocks of the fats are able to pass the intestine wall and there they are assembled into intact fats. Afterwards, they reach the lymphatic fluid and access the blood stream. One part of the fat is transported to the organs. Fats that are not needed instantly are accumulated in fat cells.

Fats are compounds consisting of glycerol and three different fatty acids.

During fat digestion, the fatty acids are separated from the glycerol that links them together. Next, the long chains are broken up into fragments. The digestion of fat is very complicated and depends upon the smooth interaction of many components.

Experiments About the Digestion of Fat

You need: 2 test tubes

Edible oil

Water

Gallic acid

Each test tube is filled with some oil and topped up with water until it is half full. Gallic acid is added to the first test tube. Afterwards, both test tubes are shaken and left for two to three minutes.

Left side: without gallic acid; right side: with gallic acid

Now the oil is dispersed in the water as small droplets.
Such a distribution is called emulsion.
In the test tube without gallic acid, the oil accumulates on the water surface.
In the test tube with gallic acid, the oil droplets remain dispersed.

You need: 3 test tubes

Water bath

Heater

Olive oil

10% sodium carbonate solution

Gallic acid

Pancreatin

Phenolphthalein solution

Each test tube is filled with olive oil and sodium carbonate solution. Then the phenolphthalein solution is added. One test tube is set aside for colour comparison. A mixture of gallic acid and sodium carbonate solution is added to the second test tube.

The second and the third test tubes are placed in a warm water bath. The same amount of pancreatin is added to both test tubes. In the second and the third test tube, the red colour of the indicator decreases. In the second test tube this process is much faster.

Fats can be split up more easily, if they are dispersed in an emulsion of fat and water.