Ovalbumin gives most of an egg white its foaming ability when the white is beaten.
Ovalbumin is the principal protein in chicken egg white, making up roughly 54% of its protein content. Beating introduces air, while the protein molecules unfold and gather around the air bubbles, helping stabilize the foam.
This property is central to foods such as meringue, soufflé, angel food cake, and whipped egg-white toppings. The foam becomes more stable when the protein network is strengthened, although excessive beating can eventually make the mixture dry and fragile.
Egg white also contains other proteins, including ovotransferrin and ovomucin, which contribute to foam formation and stability. Ovalbumin is therefore the main answer, but it is not the only egg-white protein involved. Egg yolk behaves differently because its fats interfere with stable egg-white foams.