Elizabeth-Emulsion

=__ Food emulsions __=


 * Include 2 immiscible liquids---> oil and water
 * Type of simple emulsion: a.) water in oil (w/o)---> margarine, butter b.) Oil in water ( o/w)--->mayonnaise, milk

Margarine and butter for (w/o)

Mayonnaise and milk for (o/w)


 * w/o ---> water is the dispersed phase while oil is the continuous phase
 * o/w ---> oil is the dispersed phase while water is the continuous phase

__Formation of emulsion__
Require dispersion of 1 phase into small droplets ( will increase the interfacial area) Process of homogenization--> dispersed phase broken into small droplets.



__ Mechanisms of emulsion instability __
Emulsion instability--> ability to resist changes in its physicochemical properties with time

__Mechanisms of emulsion breakdown__
Creaming--> Droplets move upwards ( droplets density< Droplets of continuous phase) Sedimentation--> Droplets move downwards ( droplets density> droplets of continuous phase) Flocculation--> >2 droplets stick together and form aggregate Coalescence--> >2 droplets merge together and form single large droplets Phase inversion--> o/w emulsion changes to w/o emulsion or vice versa.



__Emulsion stabilization__
...Can be achieved by using emulsifiers ( surfactants ) and/ or stabilizers Emulsifiers---> Facilitate formation of emulsion by lowering oil/water interfacial tension and impart short term stability, form protective film around droplets. Stabilizers---> Not surface active but impart long term stability to emulsion by restricting interfacial interactions

__ **Function of emulsifiers** __

Adsorption at interface: Emulsifiers, amphiphilic nature, absorb at the interface between oil and water and form interfacial film, meaning reduction of interfacial tension. reduction of interfacial tension through addition of emulsifiers allow emulsion formation with considerably less energy input.

Liquid crystal stabilization: Mesophase structure or liquid crystals--> mixture of emulsifiers and water. Liquid crystalline phases may form on the surface of oil droplets in o/w emulsions and reduce rate of coalecsence even if flocculation occur. Micelle --> aggregation of emulsifiers molecules, hydrophobic inside, and hydrophilic on surface.



Ionic stabilization: Charged groups on surface of emulsion droplets increases with repulsive forces. Ionic emulsifiers will form electrically charged double layer in aqueous solution surrounding each oil droplets. Thickness of electrical double layer affected by ionic strength. Low salt enhances stability, high salt increase Flocculation and/ or coalescence

Stabilization via steric hindrance : Hydrocolloids increase emulsion stablity macromolecules can act by increasing the viscosity or partitioning into o/w interface as physical barrier to coalescence

Gravitational separation: Droplets in emulsions have different density to that of liquid which surround them, net gravitational force acts upon them cause creaming or sedimentation. Droplets in o/w--> tend to cream Droplets in w/o--> tend to sediment

__ Methods of controlling gravitational separation __
match the density of oil and aqueous phases( mix natural oil with brominated vegetables oil) stability of emulsion to gravitational separation will increase Increase viscosity of continuous phase surround the droplets will decrease the velocity of droplets moving around Add thickening agent
 * Minimize density difference
 * reduce droplet size
 * Modify rheology of continuous phase