Food Dispersion Flashcards
What is an emulsion?
An immiscible liquid dispersed in small droplets in another immiscible liquid
What are the two different types of emulsions?
Oil in water (O/W) = mayonnaise
Water in oil (W/O) = butter
How is a fine emulsion made?
- Separate water and oil phases are homogenised producing a primary emulsion
- A biopolymer is added to the primary emulsion to produce a secondary emulsion
How are coarse emulsions made?
Using a bowl chopper
Give an example of a coarse emulsion.
Comminuted meat products = sausages
What is an emulsifying agent?
Acts a as a stabiliser
Stops liquids that do not normally mix from separating
Produce a bilayer type structure
Give three examples of emulsifying agents.
Proteins
Phospholipids
Sterols
What do polar and non polar groups do at interfaces?
Adsorb and form a monolayer
How do emulsifiers affect surface tension?
They lower surface tension
What is emulsifying capacity?
The rate at which the emulsifier penetrates into an O/W interface
What does the formation of a good emulsion depend on?
Contact angle of emulsifier
Interfacial tension (lower the better)
Energy required
What is the hydrophilic - lipophilic balance?
The ratio of hydrophilic to hydrophobic groups in an emulsion
What is the hydrophilic - lipophilic balance in W/O emulsions?
3 : 8
What is the hydrophilic - lipophilic balance in O/W emulsions?
11 : 20
What is surface / interfacial tension?
Forces that reduce surface / interfacial area
The lower the surface tension the ________ the surface area
Greater
Why is an increased surface area beneficial in forming emulsions?
There is more surface area to create droplets
More stable
Less ‘work’ is required
What determines whether an emulsion is W/O or O/W?
Contact angle
What is the theory of colloidal stability?
Stability depends on two types of interactions;
- Van de Waals attractions
- Electrostatic repulsion between electrical double layers of the same charge
If repulsion attraction is _______ than attraction potential the suspension will be stable.
Greater
After two droplets approach each other and flocculate, what two things can happen next?
Droplets either separate or coalescence occurs
Adsorption and interactions between ______ increases stability.
Emulsifiers
What are the methods of measuring emulsion stability?
- Measure change in dispersion - either by droplet size analysis or sedimentation rates
- Measure the charge on a droplet - by electrophoresis
- Apply stress centrifugation - by heating
What are foams?
The dispersion of gas bubbles in a liquid
Give an example of a liquid foam.
Beer
Give two examples of solid foams.
Bread
Meringues
