Emulsion Flashcards
Emulsion formed by
Emulsions do NOT form spontaneously
Energy input is required
High energy/short time (e.g. homogeniser)
Low energy/long time (e.g. paddle stirrer)
Droplet break-up due to induced turbulence
Homogeniser technology
high pressure homogeniser
Membrane emulsification
Rotor- stator (-rotor) devices
Ultrasound emulsification
Types of emulsions
= Simple emulsions (macroemulsions)
O/W or W/O
= Multiple emulsions
O/W/O or W/O/W
Stabilising emulsions
Can be stabilised by ?
Once an emulsion has been formed it must be stabilised
- initially at its time of formation
- in the longer term for product stability
stabilised by surfactant / polymer /solid particles
Emulsifiers frequently sold for which of their ability
their ability to lower surface tension
- however, it is usually their long term effects which are more important
Droplet formation equation
slide 7
Kolmogorov and Hinze:
Dm = (ε^-2/5) x (γ^3/5) x (ρ^-1/5) x(k)
Dm = smallest drop ε = energy density γ = interfacial tension ρ = density k = constant
a homogeniser can produce how much energy densities
billions of W per cubic metre
surface tension is measured in
mN
emulsifier’s primary role is NOT for ?
not on interfacial energy
Surfactants
Surface active agents occur widely in nature and have been used for over 1000 years as emulsifiers in cleaning and in foods.
Molecules with two distinct regions:
Hydrophilic head & hydrophobic tail
Three types of surfactants are usually used in food systems
a) proteins
b) polysaccharides
c) polyol derivatives of fatty acids
- Proteins found nearly all food systems
–> (c) usually in conjunction with (a) and/or (b)
they do not usually produce a system in their own right
Protein surfactant Ex & application
caseinate (O/W) Ice cream whey protein (O/W) cake batter Egg protein (O/W) mayonnaise
Polysaccharide surfactant Ex & application
Methyl cellulose (O/W) artificial cream
modified alginate (O/W) salad dressing
Small molecule surfactant Ex & application
monoglycerides (W/O) margarine
acid esters of MGs (W/O) & (O/W) bakery products
sorbitan fatty acid esters (W/O) confectionery
Kinetic view of emulsion formation
particles
a) large size small size
b) small size small size with surfactants
c) small size with surfactants small size with surfactants [Flocculation / de- flocculation]
d) small size with surfactants large size
see slide 11