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Lab 7: Eggs
Terms in this set (7)
Eggs are among the most nutritious foods known, and egg protein has the highest quality of any protein. The egg white is mostly protein and contains almost no fat. The egg yolk or embryo is mostly fat with some protein, and is also high in cholesterol.
1. An egg consists of the shell (10%), the white (60%), and the yolk (30%). The white and the yolk are each surrounded by a membrane, and the yolk is held near the center of the egg by the chalaza, a proteinaceous rope-like structure.
2. Old eggs can be differentiated from fresh eggs in a number of different ways: 1) old eggs lose moisture and have a larger air cell; 2) old eggs lose CO2 causing the pH to rise, the more basic pH causes the membrane and chalaza to deteriorate.
3. Eggs keep longest if they are stored at refrigerated temperatures in a sealed container to minimize loss of moisture and CO2.
4. Egg white proteins, along with milk proteins, are the only proteins with the necessary emulsification properties to form foams. A foam is a colloidal dispersion with a gas (usually air)as the dispersed phase, and a liquid as the continuous phase. Egg white proteins are able to function like emulsifiers at the gas¾liquid interface to stabilize the foam. Considerable force in the form of beating must be applied in to facilitate the formation of a foam.
5. Egg white foams are typically more stable than milk foams. Egg white foams can be made more stable by adding sugar or lowering the pH with an acid or both. Egg white foam can be made less stable by dilution with water and the addition of fat.
6. Frozen or refrigerated eggs and egg substitutes are now available in cardboard cartons. Frozen eggs are typically heat pasteurized prior to freezing to kill pathogenic bacteria.
How was the appearance of uncooked old eggs different from uncooked fresh eggs?
There was no membrane around the yolk in an uncooked egg that was old (it had a watery consistency), and the consistency of an uncooked fresh egg was thicker, and it had a membrane around the yolk.
Why were the floating characteristics of old eggs different from those of fresh eggs?
The old egg had a larger air pocket which caused it to float, whereas the fresh egg didn't float because its air pocket is much smaller (less than 1/8 inch).
Which ingredients produced the most stable foam? Why?
Cream of tartar produced the most stable foam because tartaric acid in cream of tartar helps stabilize the foam.
Processed eggs in cartons are now widely available in grocery stores. These eggs are cheap, and can be frozen, but typically do not form foams when beaten. What in the processing of frozen eggs besides freezing might alter their ability to form foams? Why?
Frozen eggs have been pasteurized, and the foam-forming proteins are denatured when heated.
How does the stability of egg white foams compare with the stability of milk foams created in the previous lab?
Egg white foams are typically of higher quality and are more stable than milk foams because they are higher in protein.
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