Properties of Emulsifiers
An emulsifier consists of hydrophilic (water-soluble) part and lipophilic (oil-soluble) part.
When an emulsifier is added to a mixture of water and oil, the emulsifier is arranged on the interface, anchoring its hydrophilic part into water and its lipophilic part into oil.
On the interface of water/air or oil/air, emulsifiers are arranged, reducing interfacial tension of them and making them easy to be mixed. In other words, the force to separate the oil and water turns weaker, ending up with oil and water easily get emulsified.
The hydrophilicity and lipophilicity are different among emulsifiers, and the balance between these is called HLB value which ranges from 0 to 20. An emulsifier with high lipophilicity scores a low HLB value, while other emulsifier with high hydrophilicity scores high HLB value. The behaviors and functions to water depend on HLB.
Related to Water
|Hydrophilic Part||Lipophilic Part|
|Stable Milky Dispersion||10||50||50|
Not all compounds composed of hydrophilic and lipophilic can be used as emulsifiers. If hydrophilicity in a compound is greater than lipophilicity in it, the compound will disperse into water, while one with greater lipophilicity than hydrophilicity will disperse into oil.
When the hydrophilicity and lipophilicity are well-balanced, the emulsifier exhibits sufficient effects.
Because an emulsifier has two opposite parts; hydrophilic part and lipophilic part, its solution doesn’t turn to a simple aqueous solution but a colloidal solution, whose properties greatly vary depending on its concentration. In an extremely diluted solution, there is no special change, but the emulsifiers gather on the interface and the surface tension is reduced as its concentration gets greater. As the concentration gets higher, a uniform mono molecular layer is made on the surface and the surface tension drops to the minimum. Formation of micelle is caused by assembling of excess molecules, within which lipophilic parts face to the center, and surface tension won't show any change.
The point of concentration at which micelle start to form is called critical micelle concentration (cmc). The properties of the solution change greatly when it reaches cmc.
Similar changes happen on the interface of oil and water when their interfacial tension reaches cmc.
When the concentration exceeds cmc, spherical micelles appear and disperse into water. With increasing of concentration rod-shape micelle will be formed. Finally, lamellar micelles with higher structures called liquid crystal are produced.
When a small amount of insoluble substance is incorporated in an emulsifier micelle, semi-transparent solution is produced. This phenomenon is called solubilization.
Solid monoglyceride has a large capacity of crystallization which affects its performance. It also makes a liquid crystal which has intermediate characteristics between solid crystal and liquid. The form varies with the kind of emulsifier, temperature and its concentration.
In practical use, it is necessary to select a suitable emulsifier based on conditions such as temperature and food constituents. The point is how an emulsifier binds with water and disperses in it, but it is difficult to predict the results based on equation. In actual use, to predict the results based on the empirical rules and information about emulsifier is desirable.
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