Lecture 10

Question 1

Four fractions of casein:

Answer 1

αs1 : β : κ : αs2 = 3:3:1:0.8

Question 2

αs and β caseins

Answer 2

Calcium sensitive and are very hydrophobic

Question 3

κ caseins

Answer 3

Contains only one phosphate group. Are hydrophilic because it contains an acidic carb section

Question 4

True or false. Hydrophilic κ caseins exist on the surface.

Answer 4

True

Question 5

Why do κ caseins stabilize the micelle?

Answer 5

Negative charge and
hydration.

Charged hydrophilic
carbohydrate group.

Hairlike structure which
confer steric stability

Question 6

True or False. Acid coagulation of milk proteins is a reversible process.

Answer 6

False. It is irreversible.

Question 7

True or False. Acid coagulation is accompanied by demineralization, reduction of electrostatic interactions between protein molecules, and aggregation of caseins through hydrophobic interaction and calcium bridging.

Answer 7

True

Question 8

What is the pI value of casein micelles?

Answer 8

4.6

Question 9

What is rennet-like protease?

Answer 9

Zingibain

Question 10

During enzyme-induced milk coagulation, k-casein is broken down into what?

Answer 10

CMP and para-k-casein

Question 11

What is soluble and thus diffuses away from the micelle?

Answer 11

CMP

Question 12

Para-k-casein is _____________.

Answer 12

Hydrophobic

Question 13

What is another name for zingibain?

Answer 13

Ginger protease

Optimal temp: 70°C
Temperature range: 40 to 70 °C

Question 14

What are the applications of zingibain and limitations?

Answer 14

Meat tenderizer and rennet substitute. Limitations are low stability and easily inactivated.

Question 15

What temp will be used when making ginger milk curd?

Answer 15

80 °C

Question 16

Zingibain is a substitute for _________.

Answer 16

Rennet

Question 17

What is the function of enzymes on milk protein coagulation?

Answer 17

Cleave the hydrophilic carbohydrate group on k casein and destabilize milk proteins.

Question 18

What results do we see from enzymes destabilizing milk proteins?

Answer 18

The k-casein coagulates and forms a solid curd

Question 19

Explain the principle of acid effects on milk protein coagulation.

Answer 19

Acid-induced coagulation involves the precipitation of casein.

Question 20

During acid-induced coagulation, what is involved?

Answer 20

Demineralization, aggregation of caseins, and reduction of electrostatic interactions.

Question 21

What pI does acid coagulation occur?

Answer 21

4.6

Question 22

True or false. Ultimately, enzymes reduce steric repulsion.

Answer 22

True

Question 23

Enzyme-induced coagulation cleaves k-casein resulting in ______ and ___________.

Answer 23

CMP and para-k-casein

Question 24

Why is fresh ginger juice needed to make ginger curd milk?

Answer 24

The enzyme is not very stable and is easily inactivated.

Question 25

Why did rennet 30 and 100 degrees Celsius not have good gel strength?

Answer 25

The temp was too low to activate the enzyme or too high and denatured the enzyme