lab report

Topics: Protein, Egg white, Milk Pages: 8 (2902 words) Published: November 1, 2014
FOOD NUTRITION BASICS LABORATORY REPORT LAB 3 PROTEINS DUE DATE Next FNB Practical NAME (CAPITALS) ______________________________GROUP LETTER___________ This work is the product of my own efforts and has not been copied from any other sources except where full acknowledgement has been given. Signed________________________________________ Student No._____________ Introduction The principle involved in this experiment is denaturation. It involves loss of ordered structure and can be caused by changes in pH value, salt concentration, surface effects or temperature. Denaturation occurs because the bonding interactions responsible for the secondary structure and tertiary structure are disrupted. In tertiary structure there are four types of bonding interactions between side chains including hydrogen bonding, salt bridges, disulfide bonds, and non-polar hydrophobic interactions. which may be disrupted. Therefore, a variety of reagents and conditions can cause denaturation. The most common observation in the denaturation process is the precipitation or coagulation of the protein. A. Denaturation of egg white. Result TubeContentsObservationsAwhite placed in water bath at 60C.Bwhite placed in water bath at 80C.-When the solution boiled on 3.30 minutes,the colour changes in yellow to white. -Boiled on 6.30 minutes, it becomes thick -Boiled on 11.11,it appeared some solid.CAdd 4 dropwise 1M Acetic acid in egg white.-The colour becomes creamy. -lump and white precipitates can be observed.DAdd 51 dropwise 5M NaCl in egg white.-The solution becomes cleanlyEAdd an equal volume of distilled water in egg white.-No observation change. -The egg white with distilled water just separated. Discussion In this experiment, by the differences of temperature, acid and NaCl, egg white will denature in such situation. The result shows that as temperature rises, the molecules have more kinetic energy. They vibrate more rapidly and collide with each other more frequently. Therefore from the table, rate of denaturation of egg white at 80 is faster than that at 60. The higher the temperature of the water bath, the more the heat energy is supplied to protein molecules per unit time. The average kinetic energy of protein molecules increased causes them vibrate too rapid and violent. As a result, the bond disrupts faster the rate of denaturation is increased. For the Acetic acid added in the egg white solution, the result shows the change is fast. This can be explained by the reaction between acid and egg white which causes protein denaturation by altering the electrostatic interactions. The main effect is unfolding the tertiary conformation of peptide chain, decreasing of solvation and subsequent decrease of solubility. For the NaCl added in the egg white solution, the result shows the egg white solution remains clear. It can be explained as the amount of NaCl solution is below the required amount to break hydrogen bonds. Subsequently, with the increase of NaCl solution present in the egg white solution, salt molecules readily interact with water from protein surface and remove it from the surface. The unfavourable interactions produced between protein molecules brings about the association of protein molecules. Hence, white precipitation is observed. For the distilled water added an equal volume in egg white solution. It has not observation change as water molecules do not interrupt bonds inside native conformation. Furthermore, even though egg white added 20ml of water before experiment, it doesnt matter. Because top water has ion but distilled water yet. B. Egg Custard Data 1 egg 3 tablespoons of sugar 100ml of warm milk Result After baking, the mixture changes from liquid state to semi-solid state and formed a gel-like structure. Discussion Egg Custards are generally thought of as sweet desserts. In this experiment, we can examine the phase transitions that occur in denaturation of egg and milk as affected by temperature change. Egg white...
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