The key issue in the digestion and absorption of fats is one of solubility. Lipids are hydrophobic, and thus are poorly soluble in the aqueous environment of the digestive tract. The digestive enzyme, lipase, is water soluble and can only work at the surface of fat globules. Digestion is greatly aided by emulsification, the breaking up of fat globules into much smaller emulsion droplets. Bile salts and phospholipids are amphipathic molecules that are present in the bile. Motility in the small intestine breaks fat globules apart into small droplets that are coated with bile salts and phospholipids, preventing the emulsion droplets from re-associating.The emulsion droplets are where digestion occurs. Emulsification greatly increases the surface area where water-soluble lipase can work to digest triacylglycerol. Lipase is a pancreatic enzyme that catalyzes the breakdown of fats to fatty acids and glycerol or other alcohols. Lipase is primarily produced in the pancreas, but is also in the mouth and stomach. Most people produce enough pancreatic lipase. But people with cystic fibrosis, Crohn's disease, and celiac disease may not have enough lipase to get the nutrition they need from food. Lipase is an enzyme which catalyzes the degradation of triglycerides. More generally known as Lipoprotein Lipase(LpL). This is a catabolic reaction. Lipases catalyse the breakdown of fats and oils into fatty acids and glycerol in the small intestine, with an equation of ; Fats (lipids) Fatty acid and glycerol. Lipase hydrolyses the fat in milk to fatty acids which react with sodium carbonate to lower the pH of the mixture. This pH change is observed by using phenolphthalein.


(a) Firstly , label three test-tubes 1-3.

(b) Next , using a pipette or syringe, place 5 ml milk in each tube.

(c) Rinse the pipette and use it to place 7 ml dilute sodium carbonate solution in each tube. This solution is to make the mixture alkaline.

(d) Rinse the pipette or syringe and use it to place 1 ml 3% bile salts solution in tubes 2 and 3 only.

(e) Use a dropping pipette to add phenolphthalein solution to each tube until the contents
are bright pink. About six drops will be sufficient and equal quantities should be added to each tube.
Phenolphthalein is a pH indicator. In alkaline solutions (above pH10) it is pink; in 'acid' solutions (below pH 8.3) it is colourless.

(f) In a spare test-tube, place about 15 mm of 5% lipase solution and, using a test-tube holder, heat the liquid over a small Bunsen flame until it boils for a few seconds.
Cool the tube under the tap and, using the graduated pipette or syringe, transfer 1 ml of the
boiled liquid to tube 2.

(g) With the pipette or syringe, place 1 ml unboiled lipase solution in tubes 1 and 3.

(h) Note the time. Shake the tubes to mix the contents, return them to the rack and copy
the table below into your notebook, observing the tubes from time to time.

(i) Note the time required for the contents of each tube to go white and then complete
the table of results.


Tube 1 (Lipase only): took 6 mins 42 secs to turn from pink to clear/white
Tube 2 (Boiled Lipase, Bile salts): remained pink after 15 minutes
Tube 3 (Lipase and bile salts): 2 mins and 11 secs


The result obtained is different because all three test tubes are tested with different condition and materials. From the result function of bile salts is known and what will a boiled lipase will result. Test tube 1 shows the change in phenolphthalein after 4 minutes, where you used no bile. This is the time it takes for lipase to break down ordinary fats to fatty acids and glycerol (the production of the acids causes the colour change). Test tube 2 doesnt show any changes for 15 minutes due to boiled lipase which is used to show the denaturing effect of heat on enzymes (which are proteins). Heating the lipase destroyed its structure, which in turn prevents its action. This means that no fats are converted, even in the presence of bile but emulsification still occurred in this tube. Test tube 3 took 2 minutes plus to change colour because the proper presence of lipase and bile salts which is a similar situation