Emulsifiers

Emulsifiers are amphiphilic substances that stay in the interface between the dispersed and the continuous phase to stabilize an emulsion. They also act as surfactants, since they decrease the surface tension between molecules in order to ensure that the emulsion remains mixed and stable over time (Figure 1).

Figure 1. The effect of emulsifiers. The emulsion above does not have emulsifier and both phases tend to separate over time. On the other hand, the emulsion below has an emulsifier (in purple), which keeps the emulsion stable and both phases mixed.

Proteins and phospholipids are natural emulsifiers due to their amphiphilic nature. Therefore, commercial emulsifiers are based on them. The most common commercial emulsifiers are:

• Lecithins: Also known as E322, lecithins are mixtures of phospholipids such as phosphatidylcholine and phosphatidylethanolamine, and are usually extracted from sources such as egg yolk and soybeans.

• Esters of monoglycerides of fatty acids: Also known as E472a-f, they are made from natural fatty acids, glycerol, and an organic acid such as acetic, citric, lactic or tartaric. The fatty acids are usually from a vegetable source, though animal fats can be used.

• Mono- and diglycerides of fatty acids: Also known as E471, they are semi-synthetic emulsifiers made from glycerol and natural fatty acids, which can be from either plant or animal sources.