When you heat an egg, the egg white clump together and turned white. It is because the protein in egg white undergoes denaturation, the cross linkage(the hydrogen bonds, ionic bonds and disulphride bonds) which maintain the protein shape destructed, so protein lose its tertiary conformation. This denaturing process is very important, because before protein can be used in digestion they must be unfolded. Part A: denaturation of egg white
To examine the factors on the effect of denaturation of egg white. Principle:
As protein denaturation can be cause by several factors such as temperature, pH, salt concentration. In this experiment, we are examining how these factors affect the denaturation of protein. We use egg white, which is actually a solution of protein in water in this experiment. After the egg white had been dilute, the egg white solution can be put in 60⁰C and 80⁰C water bath to test for how temperature affects denaturation. It can be record by the time need for the first change of appearance. To find out how pH of affect denaturation, we can add dropwise the actetic acid to the egg white solution. Beside, the NaCl can also be add dropwise to egg white, to test for how salt concentration cause denaturation. Count the number of drop of solution added for an appearance change to occur. Observation:
|60 ⁰C water bath |After 15 minutes, a pale yellow | | |semi-solid formed | |80 ⁰C water bath |After 2 minutes 30 seconds, a white jelly| | |like solid formed. | |1M acetic acid |After 10 drops of acid added, the | | |solution become pale yellow and clumping | | |of egg white occurs | |5M NaCl |After 27 drops of NaCl added, the | | |solution become yellow and clumping of | | |egg white occurs | |Add equal volume of water |No observable change |
Protein′s three dimension conformation is held by the interaction between its amino acids. This interaction included hydrogen bonds, ionic bonds and disulphride bonds. But in some extreme condition, such as high temperature, extreme pH, high salt concentration, the protein will be denaturate. It is because the cross linkage had been broken, the secondary and tertiary structure are alter. The protein now has primary structure as peptide bonds are strong enough not to be destructed. In our experiment, we observed that the egg white clump together after denaturation (either by heat, pH or salt concentration). It is because after the normal structure is destructed, some new bonding may be formed between proteins. They can have a big clump of proteins hooked together. That is the coagulation. In coagulation process, the egg white turned from transparent to a cloudy solution, because as the protein clump together, there are no much space for light the pass through, so it looks more cloudy. Besides, in 80 ⁰C boiling tube, the egg white turned white while at 60 ⁰C the egg white only clump to a yellow semi-solid. It is because at higher temperature more kinetic energy is provided for the molecules to vibrate, so the bondings are disrupted more greatly. So it can be concluded that a high temperature will have a stronger effect on denaturation.
Part B: egg custard
To measure the phrase transitions that occurs in denaturation of egg and milk as affected by temperature change. Principle:
Egg and milk are the main ingredients of an egg custard, through baking an egg custard, we can examine the phase transition of...