Properties of Proteins

Question 1

List the properties of proteins

6

Answer 1

Denaturation 
Elasticity 
Maillard reaction 
Solubility 
Gel Formation 
Foam Formation

Question 2

What is denaturation?

3

Answer 2

A change in the nature of a protein chain
It involves the unfolding of a protein chain which results in an irreversible change in shape
One this happens the protein often coagulates (sets or becomes hard)

Question 3

How does denaturation result in coagulation?

Answer 3

Denaturation involves the unfolding of a protein chain which results in an irreversible change in shape which often results in coagulation

Question 4

What means bring about denaturation?

4

Answer 4

Heat
Chemicals
Mechanical action
Enzymes

Question 5

How does heat bring about denaturation?

Answer 5

Heat causes protein chains to unfold and bond together which causes food to coagulate

Question 6

How do chemicals bring about denaturation?

Answer 6

By lowering or raising pH levels by the addition of acids or alkalis a protein’s structure can be denatured

Question 7

How does mechanical action bring about denaturation?

Answer 7

Mechanical action such as whipping or beating causes protein chains to unfold and brings about partial coagulation

Question 8

How do enzymes bring about denaturation?

Answer 8

Enzymes cause a change to the nature of a protein’s structure

Question 9

Give a culinary use of denaturation brought about by heat

Answer 9

Egg whites coagulate and change from translucent to opaque at 60 degrees Celsius and egg yolks coagulate at 68 degrees Celsius

Question 10

Give a culinary use of denaturation brought about by chemicals

Answer 10

A vinegar-based marinade tenderises meat by denaturising proteins

Question 11

Give a culinary use of denaturation brought about by mechanical action

Answer 11

Whipping of eggs when making a sponge cake

Question 12

Give a culinary use of denaturation brought about by enzymes

Answer 12

The enzyme rennin in rennet causes caseinogen in milk to coagulate during the making of cheese

Question 13

Describe the elastic property of proteins

Answer 13

Some fibrous proteins such as gluten in wheat are quite elastic

Question 14

Give a culinary use of the elastic property of proteins

Answer 14

Gluten makes yeast dough elastic enough to trap the carbon dioxide gas produced by yeast which helps it rise

Question 15

Describe the Maillard reaction in proteins

Answer 15

This is the non-enzymic browning of food.

It occurs when an amino acid reacts with a carbohydrate (sugar) under dry heat

Question 16

What does the Maillard reaction occur between?

Answer 16

An amino acid and a carbohydrate (sugar)

Question 17

Under what condition does the Maillard reaction occur?

Answer 17

Under dry-heat

Question 18

Give a culinary application of the Maillard reaction of proteins

Answer 18

It gives an attractive brown colour to foods such as shortbread biscuits and roast potatoes

Question 19

Describe the solubility property of the Maillard reaction

Answer 19

Most proteins are insoluble in water, apart from collagen in meat (soluble in hot water) and egg albumin (soluble in cold water)

Question 20

Give a culinary use of the solubility property of the Maillard reaction

Answer 20

Moist heat tenderises meat by converting collagen to gelatine

Question 21

Describe the gel formation property of a protein

3

Answer 21

When collagen (protein present in the bones and skin of meat) is heated it is converted to gelatine
Gelatine can absorb large amounts of water when heated as protein chains uncoil and water becomes trapped
This forms a sol and on cooling it forms a gel which is a semi-solid viscous solution with a three dimensional protein matrix in which water molecules become trapped

Question 22

What happens to collagen when it is heated?

Answer 22

It is converted into gelatine

Question 23

What protein is converted to gelatine when it is heated?

Answer 23

Collagen

Question 24

What property does gelatine have that is used in the setting of jam?

Answer 24

Gelatine can absorb large amounts of water when it is heated

Question 25

How does gelatine absorb large amounts of water?

Answer 25

When gelatine is heated it’s protein chains uncoil and water becomes trapped

Question 26

What is formed when gelatine absorbs a large quantity is absorbed

Answer 26

A sol is formed

Question 27

What is formed when a sol is cooled?

Answer 27

A gel

Question 28

What is a gel?

Answer 28

A semi-solid viscous solution

Question 29

How is a gel formed?

Answer 29

When gelatine is heated it absorbs water to form a sol which when cooled forms a gel which is a semi-solid viscous solution

Question 30

Give a culinary use of the gel formation property of a protein

Answer 30

Its setting power is useful in making cheesecakes and jellies

Question 31

Describe the foam formation property of proteins

4

Answer 31

When an egg white is whisked the protein chains unfold (denatures) and air bubbles form
The air bubbles become trapped within the unfolded protein chain which create a foam
Whisking also generates heat which sets the egg white white slightly (temporary foam)
The foam needs to be put in the oven to set permanently

Question 32

Give a culinary application of the foam formation property of proteins

Answer 32

Meringues