Emulsifiers are chemical substances added to food to produce or maintain consistency or smooth texture. Emulsifiers establish a chemical bridge between polar (water-soluble) and non-polar (oil-soluble) components of a food.

Substances containing emulsifiers are described as emulsions. To produce an emulsion, it is necessary to stabilize the suspension of small droplets of one liquid in another. The emulsifier establishes a chemical bridge between the suspended droplets and the bulk liquid.

Emulsions may be oil-in-water (O/W) or water in oil (W/O) depending on the dispersed medium. The general structures of (O/W) and (W/O) emulsions are shown below:

Oil in water (O/W) emulsion

The hydrocarbon tails of the emulsifier molecules become buried in the oil droplets, as both are non-polar. The polar heads of the emulsifier molecules have the effect of making the surface of the oil polar and so attracted to the water. Common (O/W) emulsions include homogenized milk and mayonnaise.

Water in oil (W/O) emulsion

The polar heads of the emulsifier molecules will be buried in the polar water droplets. The non polar tails of the emulsifier molecules effectively make the surface of the water droplets non-polar and so attracted to the oil. Common (W/O) emulsions include butter and margarine.

Common emulsifiers include:

glyceryl monostearate (food additive 471).

and

lecithin

Lecithin is present in common foodstuffs such as mayonnaise and ice cream. In mayonnaise it enables the oil droplets to remain suspended in water (vinegar). If lecithin were not used in ice cream it would form ice crystals and lose its smooth texture.