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Investigation to find out what effect changing the concentration of calcium ions has on the rate of coagulation of milk

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Investigation to find out what effect changing the concentration of calcium ions has on the rate of coagulation of milk Aim To determine the concentration of calcium ions at which the rate of coagulation is the fastest. Background Information Rennin, known also as Chymosin, is a proteolytic enzyme which is manufactured by stomach cells. Its role in digestion is to coagulate milk by converting caseinogen into casein, which is precipitated as calcium caseinate i Caseinogen + Ca2+ --> Calcium caseinate This process is extremely important in young animals. If the milk was not coagulated, it would flow rapidly through the stomach and miss the opportunity for initial digestion of its proteins.ii The majority of milk protein is casein and there are four major types of casein molecules: alpha-s1, alpha-s2, beta and kappa. Kappa casein is a distinctly different molecule to the others as it is not calcium-precipitable. As the casein molecules are secreted, they self-associate into aggregates called micelles. Alpha and beta caseins are kept from precipitating by their interactions with k-casein. Essentially, k-casein keeps the majority of milk protein soluble and prevents it from spontaneously coagulating. Chymosin proteolytically inactivates kappa casein, converting it into Para-kappa-casein. Para-kappa-casein does not have the ability to stabilize micelles and so the calcium-insoluble caseins precipitate, forming a curd. ...read more.


The readings were inconsistent as all the beakers were at different stages of coagulation. Therefore it was difficult to find an exact point of coagulation. c) The temperature of the milk was cold (11�C), which may have resulted in a slower rate of coagulation as rennin is found in the stomach of young calves, and operates at an optimum temperature of 37�C. To solve this problem I will use a water bath to regulate the temperature and also measure the temperature of the milk at regular intervals to ensure it is consistent. Variables To ensure a fair test I must control several variables. These are: * Use the same volume of milk throughout - 10cm3 * Use the same volume of sodium citrate (1cm3) and rennin (1cm3) * Ensure the temperature throughout the experiment (37�C) * Use the same type of milk - i.e. full fat, semi-skimmed Apparatus * Small beakers * Test tubes and bungs * 10cm3 Syringe * 1cm3 Syringe * Stop watch * Microscope slides * Full fat milk * Rennin * Calcium chloride * Distilled water * Sodium citrate * Water bath (37�C) Method I. Using a syringe, add 10cm3 of milk to each of the 5 beakers II. ...read more.


This ensures that the results obtained are as reliable as possible. The temperature was maintained at 37�C; as rennin is an enzyme found in the stomach of young mammals, where the optimum temperature is 37�C. Maintaining this temperature ensured that rennin was provided with ideal conditions to maximise its reaction rate. There my however be other factors that influence the rate of coagulation, such as ions. It is almost impossible to tell if all the Calcium ions have been removed. Also Chloride and sodium ions have an effect on rennin activity; therefore the presence of these may cause inaccuracies. Boiled rennin could be used as a control, as boiling would remove all the ions and other impurities, then the samples collected could be compared to the control which may make it easier to find a coagulation point. The rate of coagulation can be represented on the following chart. Table to show how the rate of coagulation varies as CaCl2 concentration varies Concentration (Mol) Time taken for coagulation (s) Rate of Coagulation (1/s) 1 2 3 Mean 1.00 0.75 0.50 0.25 0.00 Secondary Sources i Background Information on Rennin - page 936 - Journal of Diary Science Vol. 67 ii Background Information on coagulation - page 29 - Animals science in action - Caroline Barnes iii Background Information on Calcium ions- page 82 - Biology at work - Stephen Tomkins ?? ?? ?? ?? 1 ...read more.

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