Theory of Emulsification

Oil and water produce emulsion by stirring, however, the emulsion starts to break down immediately after stirring is stopped. The purpose of emulsification is to stabilize emulsion state by preventing break down which occurs due to creaming aggregation and coalescence. To solve these issues, decreasing size of dispersed particles, reducing the density difference of dispersion and protecting the surface of oil droplets are effective.

 Emulsification Process

---

1. During the process of emulsification, the main step is to break down the bulk liquid into small droplets and then stabilize the emulsion.

2. In a stable emulsion, the droplets remain dispersed. But due to interfacial tension, there is a tendency for droplets to coalesce and separate out.

The interfacial tension is lowered down by the addition of emulsifiers.

EMULSIFIERS or emulsifying agents are surface active agents which lower the interfacial tension, i.e. the tension at the interface of two immiscible liquids.

3. The dispersed droplets which are of colloidal dimensions tend to form spherical structures in the continuous phase.

4. To prepare a stable emulsion, it is necessary to reduce the size of the droplets, prevent their coalescing, and increase their surface area.

5. Mechanical aids such as beaters, stirrers, homogenizers and colloid mills help to reduce the size of the dispersed droplets, thereby increasing surface area.

Energy is required to work against the interfacial tension and allow the continuous phase to sketch out and cover the dispersed droplets.

6. Emulsifiers are used to reduce interfacial tension. They get absorbed at the interface.

7. In an O/W emulsion, example mayonnaise, the non-polar group of the emulsifiers is oriented towards the oil droplet and is absorbed in the outermost layer of the droplet.

8. The polar group of the emulsifiers is oriented towards the continuous phase of water (vinegar, lime juice, water from egg) surrounding the oil droplet.

9. The molecules of emulsifier surround the droplet completely forming a monomolecular layer of emulsifier (lecithin) around the droplet.

10. The oil droplet is thus protected by a film consisting of 3 layers:

1. The outermost layer of oil molecule
2. A layer of emulsifier
3. The innermost layer of water

 This protective film/layer prevents two oil droplets from coalescing when they collide.

11. Emulsions are further stabilized by electrical charges.

The ingredients used should not be chilled. Warm ingredients emulsify sooner as they are more fluid and spread or split into droplets faster.

---

Stability of Emulsion

---

The stability of an emulsion depends on the following factors:

1. The presence and type of emulsifying agent present
2. The amount or concentration of the emulsifying agent
3. The size of the droplets in dispersed phase
4. The ratio of oil and water used
5. The viscosity of the continuous phase

The presence and type of emulsifying agent present

• The most important factor which determines the stability of an emulsion is the presence of emulsifying agents.
• The emulsifying agent may be present naturally in one of the ingredients. Example lecithin is a natural emulsifying agent present in egg yolk or the emulsifying agent may be added to the emulsion.
• An emulsifying agent is a compound containing both polar and non-polar groups and is thus attracted to both phases of the emulsion at the interface.
  • Polar phase-oriented towards——-water phase
  • Non-polar phase-oriented towards——-oil

• The emulsifier forms a layer at the interface which coats the surface of the dispersed droplet completely
• The droplets do not touch each other and coalesce because of the protective layer of the emulsifying agent
• The emulsion becomes stable and does not separate out into two separate layers because of the presence of the emulsifying agent.
• The type of emulsion formed will also depend on the emulsifying agent used, and whether the polar or non-polar group on the emulsifying agent is stronger.

The amount or concentration of emulsifying agent

• The amount of emulsifier present in the emulsion should be sufficient to coat the dispersed droplets completely
• The emulsifier forms a layer at the interface which is monomolecular in thickness
• The droplets do not touch each other and coalesce because of the protective layer of emulsifying agent around each droplet
• Addition of extra emulsifying agent does not have any beneficial effects
• If the emulsifier is insufficient, all droplets will not be coated or protected and stability of the emulsion is affected

The size of the droplets in dispersed phase

• Mechanical aids such as beaters, homogenizers, and colloids mills help to reduce the size of the droplets dispersed, i.e. increases their surface area.
• The smaller the size of the dispersed droplets, the more stable the emulsion
• Homogenized milk is a stable emulsion as the size of the fat droplets are reduced.

The ratio of oil and water used

• The ratio of oil and water used or the ratio of dispersed phase to the continuous phase is important
• The continuous phase should stretch out and cover the dispersed droplets completely
• For this proper mixing, shaking or beating of the emulsion is necessary

The viscosity of the continuous phase

• A viscous continuous phase will prevent the droplets of the dispersed phase from moving freely, bumping into one another, and coalescing
• Substances that increase the viscosity of a colloidal system are called STABILIZERS. They do not orient themselves at the interface as an emulsifier but reduce the speed with which the dispersed droplets move.

---

---