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Science

Food and drink

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Emulsifiers and mayonnaise

Immiscible liquids

Immiscible liquids do not mix together. For example, if you add oil to water, the oil floats on the surface of the water. And if you shake the two together then leave them to stand, tiny droplets of oil float upwards. They join together until eventually the oil is floating on the water again. To stop the two liquids separating, we need a substance called an emulsifier.

Emulsifiers

Emulsifiers are molecules that have two different ends:

  • a hydrophilic end - water-loving - that forms chemical bonds with water but not with oils
  • a hydrophobic end - water-hating - that forms chemical bonds with oils but not with water

Lecithin is an emulsifier commonly used in foods. It is obtained from oil seeds and is a mixture of different substances. A molecular model of one of these substances is seen in the diagram.

Emulsifier molecules

The hydrophilic 'head' dissolves in the water and the hydrophobic 'tail' dissolves in the oil. In this way, the water and oil droplets become unable to separate out. The mixture formed is called an emulsion.

Emulsions

Mayonnaise and emulsion paints are emulsions, but there are others - such as the two in the table.

Components of emulsions

emulsionmajor componentminor component
butterfatwater
milkwaterfat

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