Investigation on Protein Denaturation

By y. c. pong Introduction When you heat an egg, the egg sporty clump together and turned white. It is be sire 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 conformism. This denaturing process is very important, because before protein coffin nail be used in digestion they must be unfolded. fork A denaturation of egg white Aim 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 argon examining how these factors fix the denaturation of protein. We use egg white, which is actually a solution of protein in piddle in this experiment. After the egg white had been dilute, the egg white solution can be put in 60? C and 80? C water bath to test for how temperature meets denaturation. It can be record by the time need for the first change of appearance.To find run how pH of affect denaturation, we can add dropwise the actetic irate to the egg white solution. Beside, the NaCl can to a fault be add dropwise to egg white, to test for how salt concentration cause denaturation. determine the number of drop of solution added for an appearance change to occur. Observation 60 ? C water bath After 15 minutes, a pale colour semi-solid formed 80 ?C 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 yellowness and clumping of egg white occurs 5M NaCl After 27 drops of NaCl added, the solution become yellow and clumping f egg white occurs Add equal volume of water No manifest change Discussion 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 uplifted 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 argon 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 monolithic 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 ? C boiling tobacco pipe, the egg white turned white season at 60 ? C 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 Aim To measure the phrase transitions that occurs in denaturation of egg and milk as affected by temperature change. PrincipleEgg and milk are the main ingredients of an egg custard, through baking an egg custard, we can examine the signifier transition of transition of denaturation of egg and milk as affected by temperature. Result After baking the egg custard for 30 minutes, the egg custard set to a yellow smooth gelatine. Discussion The egg custard is at liquid phase before baking, and it turn to solid phase after baking. It shows that phase transitions of liquid to solid had occur in the denaturation process of egg and milk as affect by high temperature. The egg custard has a smooth and spongy texture.In the experiment, our egg custard is do of egg, m ilk, sugar only. Through applying of heat and manipulation, custards can become a awkward and semi-rigid gel, denaturation of the egg protein, causes a clumping of proteins, is primarily contribute for the thickening of the custard. Milk, although not as important as egg, but calcium ions present in the milk are also needed in order to form thicker custard. Sugar is also important to the viscosity and gel strength of custards. Sugar tends to increase the denaturation temperature of the egg proteins returning in less stiff custard.The concentration of egg protein is proportional to the viscosity or gel strength of the custard. With increasing concentration, a custard sauce becomes more viscous and the gel strength of a baked custard firmer. A custard heated slowly begins to thicken at a lower temperature, thickens gradually over a wider temperature range and result in a smoother texture. Slow cooking can be achieved by placing the custard mixture in a water bath to warm to sure te mperature before put into the oven which has been skipped in our experimentPart C denaturation of milk Aim To examine the factors on the effect of denaturation of milk. Principle Milk protein, similar with egg white, will also undergo denaturation in extreme condition. So acid and NaCl is added to milk respectively, to observe the changes and examine how pH and salt concentration affect denaturation. Then, they are place in a 80 ? C water bath, also a figure tube is tube is put in water bath, to examine the effect of temperature on denaturation. Observation original milk pH= 6. 63 1 M acetic acid 60 drops of 1 m acid had been added The pH=4. 67 in that respect are white ppt formed. Half quantity of 1 M acetic acid added 30 drops of 1M acid added there are no observable change. And after heat for 2 minutes, there are white precipitate formed. 1 ml of 5M NaCl No observable changes soon after addition of NaCl. There are short white precipitate after heat for 8 m inutes. control No observable changes even after 20 minutes Centrifugation tube 3 layers formed.The upper layer is translucent, the middle one is white and the bottom layer is white precipitate. Discussion There are 3 layers present in the centrifugation tube after centrifugation. The upper layer is the acetic acid we added, the middle layer is the milky serum, the bottom layer is the precipitate formed bring out by the addition of acid. There are 2 major components of milk, casein and serum .The casein contains phosphorus and will coagulate or precipitate at about pH 4. 6. The serum proteins do not contain phosphorus, and these proteins remain in solution in milk at pH 4. 6. So, when acetic acid added the pH drop to 4. 69 the casein precipitate so white precipitate is seen. The addition of NaCl only cause a little precipitation, shows decrease in pH has a greater effect on milk denaturation than increase in salt concentration. There are no observable changes in control because the protein are not yet denaturated in 80 ? C.Part D yoghurt Aim To experience the making of yoghurt and the theory of formation of yoghurt. Principle As raw(a) yoghurt is made from fresh milk without other ingredient added, it can be made by simply add a little yoghurt and milk together and incubate in 38 ? C incubator, which is a suitable temperature to make yoghurt. Yoghurt can be available for sense of taste after 1-2 days. Results All milk turned into yoghurt, the sample is no longer liquid but is in semi-solid. The yoghurt is a bit sour than the original sample. DiscussionYoghurt is made by fresh milk, but often some specific bacteria strains are introduce into the milk. The bacteria ingest natural milk sugars and released lactic acid as a waste product. The acid decrease the pH and cause the denaturation of milk protein during which the cross linkage between protein break and protein uncoiled. Then, the protein will tangle into a solid mass, yoghurt formed In our ex periment, we mixed the 50 ml milk with 5 ml yoghurt to made the sample yoghurt instead of milk only . the 5 ml yoghurt is to provide the bacteria.Only a small amount of live yoghurt can is needed to inoculate a new batch of yoghurt because the bacteria can reproduce and multiple themselves during the yoghurt making process. Besides the incubators temperature is 38 ? C because it is the optimum temperature of bacteria to reproduce. The yoghurt newly made is more sour than the original sample. It may be due to the long pensiveness hours, as we had kept it over 48 hours. The bacteria ingest a higher % of milk sugar and release more lactic acid. To stop the brooding we can place the yoghurt in a refrigerator.