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An investigation into the effect of lipase concentration on the rate of lipid digestion in milk, in the presence and absence of bile salts.

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An investigation into the effect of lipase concentration on the rate of lipid digestion in milk, in the presence and absence of bile salts. Background knowledge Lipase is an enzyme which catalyses the hydrolysis of triglycerides (lipids) into fatty acids and glycerol. In humans, lipid digestion begins in the stomach with lipase in the gastric juice, but mostly occurs in the duodenum and ileum upon the addition of pancreatic juice (containing more lipase) and bile (containing bile salts). Lipid digestion is illustrated in this investigation by the fact that when the lipids in milk are digested, fatty acids begin to accumulate, and the pH of the solution is lowered due to this build-up (this may be observed by the use of an indicator or pH meter). To expand on the point earlier that bile is released into the duodenum, it should be explained that the bile salts which it contains do not hydrolyse lipids as lipase does, but emulsify fat droplets into tiny globules, providing a greater surface area for lipase action; they aid lipase, as opposed to replicating its function. Bile salts are derivatives of cholesterol, and consist mostly of sodium glycochlolate, and sodium taurocholate. ...read more.


Bile salts are released into the duodenum, where they emulsify fats to aid lipase action. Test tubes 6 These will act as the reaction vessel. Test tube rack 3 To hold test tubes when not in the water bath. Thermostatically controlled water bath at 30�C 1 To ensure a constant temperature. Temperature is known to affect rate of reaction and is therefore a potential variable in this investigation which must be controlled. Distilled water 36cm3 This will be added to the set of tubes not containing bile salts, to ensure a constant volume in all test tubes. pH meter 1 A pH meter will give an accurate digital reading of the pH of a solution at any given point. As fatty acids accumulate through lipid digestion, they lower the pH of the solution. By stating an end pH for the reaction, we can accurately see when this has been reached, removing the subjectivity associated with determining an end point by means of using an indicator (e.g., phenolphthalein). Graduated pipettes 5 5 cm3 To accurately measure out volumes of the reactants; bile salts, milk, lipase and water, and to avoid cross contamination. As the volumes of bile salts, milk and lipase and considered variables in this reaction, it is important to keep their volumes as accurate as possible to produce the most reliable results. ...read more.


The experiment will now be undertaken in the absence of bile salts, to observe the different in rate of reaction which they allow. 1. Set up 6 test tubes, each containing 2cm3 of distilled water, and 5 cm3 of milk. 2. Repeat the procedure exactly as with that in the presence of bile salts, including allowing the test tubes and the pH meter to equilibrate, adding the lipase solutions one by one and recording the time taken for the solutions to reach pH 4, and repeating the procedure 3 times over. 3. Record the results in a table as previously, making sure to state that the experiment was carried out in the absence of bile salts. Risk assessment The risks in this procedure are minimal. * At 30�C, the water bath does not pose any threat for scalding or burns. * Bile salts may only be harmful in ingested in large quantities, and may irritate the eyes. * The lipase solution may irritate the skin, but given the low concentrations being used, it is unlikely to case any damage. Wash the skin is contact should occur, and wear plastic gloves. Sources 1 Cambridge Advanced Sciences: Biology 1, pages 42 - 44. 2 http://www.rsc.org/education/teachers/learnnet/cfb/images/07C.jpg 3 Cambridge Advanced Sciences: Mammalian physiology and behaviour, pages 7 - 8. 4http://www.ilri.org/InfoServ/Webpub/Fulldocs/ILCA_Manual4/Milkchemistry.htm ...read more.

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