Why is mayonnaise an emulsion?

Mayonnaise is an emulsion because it is a mixture of two immiscible liquids, oil and water, that are stabilized by an emulsifier. In mayonnaise, the emulsifier is egg yolk, which contains lecithin. Lecithin is a phospholipid, which is a type of molecule that has both hydrophilic (water-loving) and hydrophobic (water-hating) parts. The hydrophilic parts of lecithin orient themselves toward the water in the mayonnaise, while the hydrophobic parts orient themselves toward the oil. This creates a barrier between the two liquids, preventing them from separating.

In addition to lecithin, mayonnaise also contains other ingredients that help to stabilize the emulsion, such as mustard, vinegar, and salt. Mustard and vinegar help to lower the pH of the mayonnaise, which makes it more acidic. This acidity helps to protonate the lecithin molecules, which makes them more hydrophilic. Salt also helps to stabilize the emulsion by increasing the ionic strength of the mayonnaise. This makes it more difficult for the water and oil droplets to come together and coalesce.

As a result of these factors, mayonnaise is a stable emulsion that can be used in a variety of dishes.