Investigation to see what effect the changing the concentration of calcium ions has on the rate of coagulation of milk by Rennin.

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Aim :  Investigation to see what effect the changing the concentration of calcium ions has on the rate of coagulation of milk by Rennin.

Theory

Most milk proteins are caesins, which have four major forms: alpha-s1, alpha-s2, beta and kappa caesins. Alpha and beta caesins, when left on their own would precipitate in the presence of calcium. However, when associated with unperceivable kappa caesins, also present in milk, they form micelles which remain dissolved. (ref1)

Rennin digests kappa casein, preventing it from aggregating the alpha and beta caesins into soluble micelles, effectively causing them to precipitate out naturally.(causing coagulation) And this precipitation requires calcium ions.

Apparatus

Rennin solution (50-100ml)

Milk 2ml per 20cm³ of milk.

Sodium citrate solution, 2cm³ (per test tube)

1.0 mol dcm³ Calcium chloride solution

Hot water bath set at 37°C

 5 Test tubes

 5 Pipettes        

1 test tube rack

Stop watch, to measure the time taken for the flecks or curd to appear.

Safety goggles, to protect eyes from harmful chemicals.

 Syringes

Slides, to dip into beaker/test tube.

 

Introduction

  The problem that I am faced with is to get a sample of milk and try changing the concentrations of the calcium ions that are present in it.

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This can be done by adding 1cm³ sodium citrate solutions to the milk. If I want to increase the increase the concentration of calcium ions then I can simply add calcium chloride solution into the milk which shall provide me with the calcium ions.

  In this investigation my independent variable will be the calcium ion, whose concentration I shall change.

The dependant variable will the rate of coagulation, or the time it takes for the flecks of

curd to appear. I shall keep the rennin solution constant, i.e., use the same volume of it each time.

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