The mayonnaise is an emulsion between vitellus (egg yolk) and oil, which means that the particles of the yolks are dispersed in the oil. Beating the egg consist in breaking down the proteins bond such they mix more easily with the water and the lipids coming from the oil.
To facilitate the preparation of mayonnaise salt (Na +, Cl -) is added to the mixture to increase the electrostatic forces and lemon juice can also be added to decrease the pH of the mixture.