Question

Pre-Lab ( LACTOSE)

1. What does heat and/or acid do to proteins like casein?

2. What is the purpose of adding calcium carbonate after removal of the casein?

3. Explain the purpose and function of the addition of ethanol to the aqueous solution.

4. Draw the structure of lactose. Is it a mono-, di-, oligo-, or polysaccharide?

5. If lactose were hydrolyzed (broken apart into its component sugars) what sugars would be isolated?

Answer 1

1. Milk is an excellent source of protein. Because proteins have a large molecular structure, they do not dissolve in water. The proteins in milk are a colloidal dispersion. Colloidal dispersions are explained in the egg unit. There are two kinds of milk proteins: casein and whey or serum. Casein are approximately 80% of the milk proteins, and whey or serum proteins make up the other 20%.  

The light reflected from the micelles makes the milk white. Casein proteins are coagulated by acids. If an acid is added to milk, the casein proteins separate from the rest of the liquid and the milk curdles. Casein proteins are not effected very much by heat, however.

Casein proteins in milk cluster together and work like tiny sponges to hold water in the milk. They can contain and hold as much as 70% water in each protein cluster (see CASEIN PROTEIN CLUSTER ILLUSTRATION in Resources). Acids, salt, or high heat will cause the casein protein clusters to lose water.

The serum proteins, also called whey, are in colloidal dispersion in the water content of milk and are coagulated by heat, but acids and salt do not coagulate them. This is important in making yogurt and cheese

2. the casein has been removed, the excess acetic acid is neutralized with calcium carbonate,

we will separate several of the chemical substances found in milk. First, you will isolate a phosphorus-containing protein, casein. The remaining milk mixture will then be used as a source of a sugar, α-lactose. After you isolate the milk sugar, you will make several chemical tests on this material. Fats, which are present in whole milk, are not isolated in this experiment because powdered nonfat milk is used.

First, the casein is precipitated by warming the powdered milk and adding dilute acetic acid. It is important that the heating not be excessive or the acid too strong, because these conditions also hydrolyze lactose into its components, glucose and galactose. After the casein has been removed, the excess acetic acid is neutralized with calcium carbonate, and the solution is heated to its boiling point to precipitate the initially soluble protein, albumin. The liquid containing the lactose is poured away from the albumin. Alcohol is added to the solution,

3.Lactose can be removed from whey (milk without fats and proteins) by adding Ethanol. Lactose is insoluble in Ethanol, and when the Ethanol is mixed with the aqueous solution, the Lactose is forced to crystallize. Finally, it should be noted that as represented above, the number one Carbon of both Glucose and Galactose exist as hemiacetal functionalities. This functionality is labile and can exist in equilibrium with the aldehyde and alcohol that form it.

4. It is a Disaccharide

5.  If lactose were hydrolyzed , then galactose and glucose were isolated

5.