Emulsions: Principles and preparation - Physical stability of emulsions - Common physical instability issues

7 important questions on Emulsions: Principles and preparation - Physical stability of emulsions - Common physical instability issues

What are 4 destabilisation mechanisms of emulsions?

  • Gravitational separation: creaming/sedimentation
  • Flocculation
  • Coalescence
  • Ostwald ripening

How can the gravitational separation be slowed down?

Stokes law.
  • By decreasing the droplet size
  • By increasing the viscosity of the continuous phase

When does bridging flocculation take place?

In biopolymer-stabilised emulsions with a limiting biopolymer concentration.
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When does depletion flocculation take place?

May occur in the presence of high concentrations of excess emulsifier.

What are the consequences of flocculation on the physical properties of food emulsions?

  1. Increase in effective dispersed phase particle size, which may enhance the rate of gravitational separation
  2. The flocs entrap a fraction of the continuous phase --> the viscosity will increase
  3. Formation of a 3D network of droplets --> gelled product

Are flocculation and coalescence reversible?

Flocculation --> yes
Coalescence --> no

Why is Ostwald ripening often a negligible cause of physical destabilisation of food emulsions?

Because the solubility of triacylglycerols in water is extremely low.

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