Download Disperse system

Food Chemistry
Chapter 17 in Green / Damjii
Chapter X in Nuess
Chapter X in Oxford Study
(no resource in Chang)
F.6: Texture
Homework
• Read F6– Texture pp. 487-488
• Do Qs 38-42
• on p 493
F.6.1: Describe a dispersed system in food
TEXTURE depends on
– Physical properties (hardness, elasticity)
– Cooking
– Moisture content
CREAMY TEXTURES valued in many foods depend on
Disperse system
stablized (do not separate… or separate v. slowly)
macroscopically homogeneous mixture of 2
immiscible phases
A typical FOOD disperse system will involve a liquid
as one of the immiscible phases.
F.6.2: Distinguish between the following types
of dispersed systems – suspensions, emulsions,
and foams in foods.
Dispersed system: LIQUID / SOLID
Suspension (sol)
 Solid particles suspended in a liquid
 EX: blood (solid red/white blood cells
suspended in plasma)
Gel
 Liquid particles suspended in a solid
 EX: fruit jelly – water trapped in a protein
matrix
Dispersed system: LIQUID / GAS
Foam
 Gas trapped in a liquid medium
 EX: whipped cream, egg whites
Aerosols
 Liquid droplets suspended in a gas
 EX:
Dispersed system: LIQUID / LIQUID
Emulsion
 Stable blend of 2 immiscible liquids
 EX: mayonnaise (oil droplets suspending in
water)
 Emulsifiers are often used to promote the
mixing of 2 phases…
F.6.3: Describe the action of emulsifiers
Emulsifiers
 molecules that can bond to both phases
 found at the surface between the phases
 often called surfactants
 similar to what happens with soap !
Soap

Soap
F.6.3: Describe the action of emulsifiers
Emulsifiers
Lecithin – a phospholipid which is found in egg yolks
Contains polar end… hydrophilic
• Bonds to water
Contains nonpolar end… hydrophobic
• Bonds to non aqueous phase
 ex: mayo made by beating oil and
vinegar with egg yolks
• hydrophilic end of lecithin bonds to
vinegar and hydrophobic end bonds
to oil
• Surfactant (lecithin) surrounds oil
droplets… suspending them within the
aqueous phase ( vinegar ).
F.6.3: Describe the action of emulsifiers
Stabilizers
Often added to stablize dispersed states… keep
them from separating.
Inorganic phosphates (trisodium phosphate) can
stablize emulsions
Metal bowls – chefs prefer these to beat egg
whites… minute traces of the metal are
incorporated into the foam and actually stabilize it.