Food Dispersion

Question 1

What is an emulsion?

Answer 1

An immiscible liquid dispersed in small droplets in another immiscible liquid

Question 2

What are the two different types of emulsions?

Answer 2

Oil in water (O/W) = mayonnaise

Water in oil (W/O) = butter

Question 3

How is a fine emulsion made?

Answer 3

1. Separate water and oil phases are homogenised producing a primary emulsion
2. A biopolymer is added to the primary emulsion to produce a secondary emulsion

Question 4

How are coarse emulsions made?

Answer 4

Using a bowl chopper

Question 5

Give an example of a coarse emulsion.

Answer 5

Comminuted meat products = sausages

Question 6

What is an emulsifying agent?

Answer 6

Acts a as a stabiliser
Stops liquids that do not normally mix from separating
Produce a bilayer type structure

Question 7

Give three examples of emulsifying agents.

Answer 7

Proteins
Phospholipids
Sterols

Question 8

What do polar and non polar groups do at interfaces?

Answer 8

Adsorb and form a monolayer

Question 9

How do emulsifiers affect surface tension?

Answer 9

They lower surface tension

Question 10

What is emulsifying capacity?

Answer 10

The rate at which the emulsifier penetrates into an O/W interface

Question 11

What does the formation of a good emulsion depend on?

Answer 11

Contact angle of emulsifier
Interfacial tension (lower the better)
Energy required

Question 12

What is the hydrophilic - lipophilic balance?

Answer 12

The ratio of hydrophilic to hydrophobic groups in an emulsion

Question 13

What is the hydrophilic - lipophilic balance in W/O emulsions?

Answer 13

3 : 8

Question 14

What is the hydrophilic - lipophilic balance in O/W emulsions?

Answer 14

11 : 20

Question 15

What is surface / interfacial tension?

Answer 15

Forces that reduce surface / interfacial area

Question 16

The lower the surface tension the ________ the surface area

Answer 16

Greater

Question 17

Why is an increased surface area beneficial in forming emulsions?

Answer 17

There is more surface area to create droplets
More stable
Less ‘work’ is required

Question 18

What determines whether an emulsion is W/O or O/W?

Answer 18

Contact angle

Question 19

What is the theory of colloidal stability?

Answer 19

Stability depends on two types of interactions;

• Van de Waals attractions
• Electrostatic repulsion between electrical double layers of the same charge

Question 20

If repulsion attraction is _______ than attraction potential the suspension will be stable.

Answer 20

Greater

Question 21

After two droplets approach each other and flocculate, what two things can happen next?

Answer 21

Droplets either separate or coalescence occurs

Question 22

Adsorption and interactions between ______ increases stability.

Answer 22

Emulsifiers

Question 23

What are the methods of measuring emulsion stability?

Answer 23

1. Measure change in dispersion - either by droplet size analysis or sedimentation rates
2. Measure the charge on a droplet - by electrophoresis
3. Apply stress centrifugation - by heating

Question 24

What are foams?

Answer 24

The dispersion of gas bubbles in a liquid

Question 25

Give an example of a liquid foam.

Answer 25

Beer

Question 26

Give two examples of solid foams.

Answer 26

Bread

Meringues