4C_BioPT+Lab+Report

Biology Performance Task: Gut Busters Report

**Hypothesis** You can’t make the egg white foam to eight times its original volume by whisking it in a plastic bowl.

Independent variable: the type of bowl used to whisk the egg white Dependent variable: the resulting volume of egg white Control: the metal bowl

**Background Research** The albumen, or egg white, is the almost clear liquid that surrounds the yolk, and accounts for about 66% of the egg’s weight and 57% of the egg’s protein. Four alternating layers of thin and thick albumen contain approximately 40 different proteins, the main components of the egg white in addition to water.

The proteins in egg white are globular proteins, which means that the chain of amino acids are twisted and folded and curled up into a spherical shape. Weak chemical bonds keep the protein curled up tight. Egg white protein contain both hydrophilic and hydrophobic amino acids. While it is curled up, the hydrophobic amino acids are packed in the center, away from the water, while the hydrophilic amino acids are on the outside.

Beating the egg white is actually incorporating air bubbles into the mixture. When a protein is exposed to a water bubble, it uncurls, or denatures, so that its hydrophobic amino acids will be on one side next to the water, while the hydrophilic ones will be exposed to the air. The infolded proteins can then bond to one another to form stabilizing protein films. After a while, these solitary proteins become a network of interconnected proteins that trap the air bubbles. The more you whisk, the smaller and more numerous these air bubbles become, and the stiffer the foam.

Any traces of grease, such as egg yolk, can cause the whites to rise to only one-third of their potential volume, because the fat intervenes in the formation of protein bonds in the egg foam. It acts as ‘competition’ to the air bubbles, as they hydrophobic molecules will turn towards it as well, preventing the proteins from fully denaturing.

Many cookbooks warn against using plastic bowls, as they often harbor grease. This is because plastic has a porous surface, with many small minuscule bumps on it that traps grease very easily, preventing the egg white from rising to eight times its volume. However, this can be prevented by wiping everything down with a paper towel dampened with lemon juice or vinegar, and then rinsing and drying throughly.

**Methodology** Materials required: 200ml of egg white (about 5 medium eggs) 1 large plastic bowl 1 large metal bowl (roughly the same size as the plastic bowl) 1 electronic mixer 1 measuring cup Scotch-tape


 * 1) Measure 800ml of water, and pour it into the metal bowl. Mark the water level using scotch tape, and then pour the water out and wipe the bowl dry.
 * 2) Pour 100ml of egg white into the bowl.
 * 3) Beat it at medium speed for 2 minutes, then increase the speed and beat until you can lift the whisk, and leave soft peaks behind. Also check to see that you can turn the bowl upside down without the egg white spilling out.
 * 4) Level out the egg-white, and check to see if it crosses the 800ml mark.
 * 5) If it does not, pour the foam into a measuring cup and record its volume.
 * 6) Repeat with the plastic bowl.

**Results**

trial 1 |||| trial 2 |||| trial 3 || passed the 800ml mark || volume || passed the 800ml mark || volume || passed the 800ml mark || volume || metal || ✓ || >800ml || ✓ || >800ml || ✓ || >800ml || plastic || ✕ || 600ml || ✕ || 680ml || ✕ || 700ml ||

//Fig 1: table of results of the experiment//

I used the set-up with the metal bowl, to check that egg white can actually foam to 800ml, or eight times its volume. All 3 times, it did, which proved that it is possible. However, the egg whites that were whipped in the plastic bowl did not foam to 8 times its volume, foaming to an average volume of 660ml.

This confirms my hypothesis that egg white cannot foam to eight times its original volume when whipped in a plastic bowl, due to the fact that plastic bowls trap grease, which prevents the egg white from rising as much.

However, my results might not be that accurate as it there were some limitations. Firstly, I cracked the egg white into a plastic measuring cup, so some grease might have gotten into the egg whites, preventing it from rising to its maximum potential. I should have poured it into a metal measuring cup, or cleaned the measuring cup with a cloth wiped in lemon juice before hand. Also, the scotch tape I taped onto the bowls in order to mark out the 800ml mark might have ‘contaminated’ or reacted with some of the egg-whites, hence interfering with the experiment.

 //Fig 2: a picture of whipped egg white in the metal bowl Fig 3: whipping the egg white in the plastic bowl//

**References**

Exploratorium, //Science of Egg: Anatomy of an Egg//. [|__http://www.exploratorium.edu/cooking/eggs/eggcomposition.html__], accessed 17/07/10.

Exploratorium, //Science of Egg: Egg Science//. , [|__http://www.exploratorium.edu/cooking/eggs/eggscience.html__] accessed 17/07/10.

Your Mother Was A Chemist, //Protein Chemisty//. [|__http://kitchenscience.sci-toys.com/protein__], accessed 17/07/10

Asian Online Recipies, //Cooking with Egg Whites//. [|__http://www.asianonlinerecipes.com/cooking_guide/cooking-egg-whites.php__], accessed 15/07/10.

Charles E. Ophardt, Elmhurst College (2003), //Denaturation Protein//. [|__http://www.elmhurst.edu/~chm/vchembook/568denaturation.html__], accessed 15/07/10.

Delia Smith (2005). The Delia Collection, Baking. BBC Books, England.

Stephanie and Rick Jaworski, The Joy of Baking (2003), //Eggs//. [|__http://www.joyofbaking.com/eggs.html__], accessed 14/07/10