Emulsions+Destabilisation


 * Emulsion Destabilisation **

**1. Creaming **

During storage, due to the density differences between most edible oils and water, oil phase might be concentrate at the top of the food emulsion- Creaming. The process is reversible, with only gentle stirring is necessary to restore the original emulsion.

Creaming does not destabilize the emulsion, but high conc. of droplets in the creamed layer promotes interactions that lead to flocculation and coalescence.

The rate of creaming can be lowered by reducing the droplet size, lowering the density difference between oil and the aqueous phase, and increasing the viscosity of the medium. The creaming rate also dependent on the volume fraction of the dispersed phase and usually slow in conc. emulsions. It is usually involve in o/w emulsion with 0.1< Φ < 0.5 and droplet size from 2 to 5µm.

**2. Flocculation **

Flocculation is defined as process by which two or more droplets aggregate without losing their individual identity. Larger droplets will flocculate faster and it is promote by creaming. It can be also affected by the pH and ionic strength of the aqueous environment. Interactions among protein, polysaccharide and water soluble surfactants can also affect the stability of the emulsion.

Bridging flocculation occurs in the presence of macromolecular in an emulsion. When there is insufficient emulsifier in the emulsion, large surfactant molecules will adsorb to two different droplets. Bridging flocculation causes an emulsion to cream more rapidly.

Depletion flocculation: Polysaccharides that introduce into emulsion to control the viscosity and yield stress, which are not surface active, maybe too large to fit in to the space between emulsion droplets, and then exert an osmotic effect that pulls water from between the emulsion droplets.

**3. Coalescence **

Coalescence is the process when two or more droplets collide to each other and results in the formation of one larger droplet and is dominating when Φ is high. Coalescence involves breaking the interfacial film and is irreversible. It can be affect by solubility of the emulsifier, pH, salts, emulsifier concentration, phase-volume ratio, Extensive droplet coalescence can lead to the formation of a separate layer of oil on top of a product, which is known as “oiling off”

**4. Ostwald Ripening **

Ostwald ripening occurs with polydispersed droplets. Collisions between two droplets may lead to one bigger droplet and one smaller one. Eventually, the small droplets become very small and become solubilized in the continuous medium. High solubility of the oil in the aqueous phase is required; therefore Ostwald ripening is uncommon in food where triglycerides are not normally soluble in water but it do occurs rapidly in frozen foods and in w/o emulsion where water is partially soluble in polar triglyceride oils.

**5. Phase Inversion **

The viscosity of an emulsion will increase gradually as more and more of a given phase is added until a critical volume is reached. If it exceeding the critical volume, emulsion will invert, i.e., the discontinuous phase will become the continuous phase.

**<span style="font-family: 'Times New Roman',serif;">6. Ionic Strength **

<span style="font-family: 'Times New Roman',serif;">It is an important factor determining the repulsive energy between droplets. <span style="font-family: 'Times New Roman',serif;">The lower the conc. of inorganic electrolytes (salts), the higher will be the repulsive energy and more stable the emulsion toward flocculation (aggregation). <span style="font-family: 'Times New Roman',serif;">This property leads to compromises between flavor and stability.