Question

Lecithin (mixture of phospholipids) is used in cooking to stabilize emulsion (dispersion of a liquid as small droplets in another, immiscible liquid). Explain the interactions involved. )

Answer 1

1)Lecithin is an emulsifier made up of about five smaller molecules. It has a backbone of glycerol that bonds up to three other molecules. Two of the bonded molecules are fatty acids -- these are hydrophobic. They give lecithin a structure similar to fats, or lipids.

2)The third substance attached to glycerol is phosphoric acid that has an amino alcohol attached called choline. The phosphate/amino alcohol end of lecithin is hydrophilic.
emulsifiers are molecules that contain both a hydrophilic, water loving, and hydrophobic, water hating, portion. So, lecithin is a molecule with one end that is hydrophilic and another that is hydrophobic.

3) "Lecithin makes a good emulsifier because the hydrophobic end dissolves in oil droplets and the hydrophilic end dissolves in water. In emulsions the only place lecithin likes to be is at the edge of oil droplets with its hydrophobic end in the oil and the hydrophilic end in the water.". Oil droplets in water are protected in the same way by lecithin so the emulsion stays stable for a long time.