Lecture 4 & 5

Question 1

Properties of whey protein

Answer 1

1. ordered structure > heat sensitive
2. hydrophobic, polar and charged (net negative charge at pH of milk)
3. High in sulfur

Question 2

Properties of A-lactoalbumin

Answer 2

Binds to Ca2+ and able to fold/unfold reversibly when heated

Question 3

Properties of B-lactoglobulin

Answer 3

Presence of disulfide bonds and sulfhydryl groups
Unfolds irreversibly when heated
Participates in disulfide-sulfhydryl reactions with potassium

Question 4

Properties of kappa-casein

Answer 4

Forms a protective layer to help casein micelles remain in its micellar form
Non calcium binding
Amphipathic structure with inert polar domain

Question 5

Role of calcium in casein

Answer 5

When casein lose structural integrity perhaps due to change in acidity, presence of free calcium acts as a stronger group to strengthen the protein network

Question 6

Functionalities of casein micelles

Answer 6

1. Provide fluidity to casein molecules, stabilise phosphate and calcium.
2. Prevent formation of calcium stones in mammary gland
3. 2/3 of calcium in present in casein micelles, 1/3 of calcium are present in the serum
4. Kappa casein prevent protein aggregation? (read up)
5. Gives milk its heat stability because it is the dominant protein in milk
6. Excellent kappa casein protective layer
7. Stabilize other food proteins
8. Emulsifying properties
9. Contains essential amino acids > nutrition
10. Amphiphilic > ideal for encapsulation of food bioactive compounds > casein structure not modified (e.g. Beta casein has hydrophobic binding sites that is able to encapsulate bioactive food materials)
11. Good carriers of inorganic elements such as calcium, magnesium, zinc

Question 7

What happens when kappa casein is disrupted?

Answer 7

They lose stability they tend to aggregate > coagulate milk proteins to form cheese

Question 8

What is the protein efficiency ratio?

Answer 8

It determines the effectiveness of a protein through the measurement of animal growth. Weight gain of tested rat subjects are compared to a standard value of casein protein at 2.7

PER > 2.7 = excellent protein source

However, it does not have a strong correlation to humans

Question 9

What is the biological value (BV)?

Answer 9

measures protein quality by calculating the nitrogen used for tissue formation divided by the nitrogen absorbed from food as a percentage of nitrogen utilized.

Provides a measurement of how efficient the body utilizes protein consumed in the diet.

High BV = high amounts of essential amino acids

However, The biological value does not take into consideration several key factors that influence the digestion of protein and interaction with other foods before absorption. The biological value also measures a protein’s maximal potential quality and not its estimate at requirement levels.

Question 10

What is net protein utilization?

Answer 10

Direct measure of retention of
absorbed nitrogen from nitrogen ingested

Question 11

Protein digestibility corrected amino acid score

Answer 11

protein quality could be determined by expressing the content of the first limiting essential amino acid of
the test protein as a percentage of the content of the same amino acid content in a reference pattern of essential amino acids

Reference values are based on the essential amino acids requirements of preschool children

provides a measure of the quantity of various proteins using these protein rating scales

Most widely used and accepted method, but limitations include overestimation in elderly and influence of ileal digestibility