Casein and Whey protein

Question 1

CASEINS: properties and characteristics

Answer 1

• 80 % proteins in cow milk (300nm)
• Random-coil proteins (no fixed secondary or tertiary structure). Because of the proline residues –> no alfa-helices and B-sheets.
• Micelles–> macro-micelles.
• Casein protein molecules are phosphorylated.

Question 2

ISOLATION METHODS FOR CASEIN PREPARATIONS:

Answer 2

Precipitation by acid/rennet or filtration: filtrate–> whey proteins (globular) and retentate–> caseins (random coil)

Question 3

Separation of whey and caseins from milk:

Answer 3

Precipitation by acid/ rennet or filtration:

• Filtrate: whey proteins (globular)
• Retentate: caseins (random coil)

Question 4

At what pH the caseins micelles are considered to be soluble ? And why? What happen if either factor is changed?

Answer 4

pH= 6.7
This mean that they not precipitate=sediment, under normal gravity. This is because at this pH, there is electrostatic repulsion between the different casein micelles. It is also due to the presence of the carbohydrate chains of the k-casein, which result in positive interaction with the water.
If it is changed (lowering pH–>decreasing net charge, or by rennet which removes the carbohydrate chain) the caseins precipitate.

Question 5

WHEY PROTEINS: properties and characteristics.

Answer 5

Is obtained after separation of lipids and caseins from the milk.
*Globular molecules mixed.

Question 6

ISOLATION OF THE WHEY PROTEIN:

Answer 6

Whey protein can be spry-dried or further purified to remove lactose. A further separation, chromatography, can separate alfa lactalbumin and B-lactoglobulin.

Question 7

Difference between whey protein concentrates and whey protein isolates:

Answer 7

• Whey protein concentrate 35 until 80% protein. It is important to realize what the other compounds are. Varations in lactose can result in varation in protein modification due to processing because of Maillard reactions.
• The whey proteins isolates have a higher protein content >90% protein, but still contain different types of proteins.

Question 8

The proline residues are known to …….

Answer 8

Interrupt the alfa/helical and B/sheet structures in globular proteins.