Emulsifiers
Functionality
Emulsifiers are functional ingredients with both lipophilic and hydrophilic properties at once: their molecular structure has a hydrophilic and a hydrophobic part.
An emulsion is a dispersion of droplets of one non-miscible liquid into another – i.e., water and oil. Without an emulsifier, the two liquids would quickly separate.
The emulsifier is absorbed in the interface between the two liquids, forming a film between both products: due to their structure, the polar part of the emulsifier molecule has an affinity with water and the non-polar part (fatty chain) tends to be attracted to the fatty phase. The emulsifiers force one of the liquids into separate drops, suspended and dispersed within the other liquid. Because these droplets are “guarded” by the emulsifier molecules surrounding them, they are kept apart from each other, ensuring the two substances do not separate but are kept in a stable mixture.
Figure 1: Emulsions
The above diagram in Figure 1 shows the barrier between the oil and water in a mixture. The emulsifying molecule is shown with its hydrophilic (polar) “head” buried in the water, while it’s lipophilic “tail” is attracted to the oil phase. This process encourages the formation of mutually repellent droplets, as shown in Figure 2.
The hydrophilic /lipophilic characteristics of emulsifiers are normally standardized by their HLB value (Hydrophilic/Lipophilic Balance). Emulsifiers with a strong lipophilic character have a low HLB, while those with a stronger hydrophilic value have a high HLB.
According to their HLB value, emulsifiers can be classified as follows:
HLB |
Emulsifier |
1 |
Polyglycerol polyricinoleate |
2 |
Sorbitan tri-stearate |
3 |
Mono-diglycerides of fatty acids |
4 |
Polyglycerol stearate |
5 |
Sorbitan mono-stearate |
6 |
Sorbitan mono-palmitate |
7 |
|
8 |
Sorbitan mono-laurate |
9 |
|
10 |
Citric Acid Ester of MG |
11 |
|
12 |
Citric Acid Ester of MG |
13 |
|
14 |
|
15 |
POE 20 sorbitan mono-oleate, POE 20 mono-stearate |
16 |
POE 20 sorbitan mono-laureate |
This value is used as a guide when selecting an emulsifier for a given application. Emulsifiers with a low HLB are suitable for water-in-oil (W/O) emulsions, while those with a high HLB are more suitable for oil-in-water (O/W) emulsions.
Figure 2: Types of emulsion
Others properties of emulsifiers in food include:
- interaction with starches (bread, mashed potatoes, pasta)
- coating capacity
- foam stabilization (cakes, toppings, whipped cream)
- fat bloom retard (chocolate, margarine)
- viscosity control (chocolate, sweets)
- solubilizing agent (flavours, oleoresins).