How does an egg yolk act as an emulsifier in mayonaise?
To make mayonnaise you need to mix oil and vinegar. Normally the oil would float on top of the vinegar and the two liquids would not mix because vinegar contains water. There are long molecules in egg yoke that have a water loving (hydrophilic) head and a water hating (hydrophobic) tail. When the egg yolk, oil and water are whisked together the oil forms small droplets that float in the vinegar. The tails of the long molecules in the egg yolk are repelled by the water and bury themselves in the oil droplets to get away from the water, but they leave their heads sticking out. This helps the oil droplets and water stay mixed together and prevents separation. This is called emulsification and the egg yolk is acting as an emulsifier.
