Egg white is the clear part of the egg, which turns white when cooked. Egg whites consist of five different
proteins: ovalbumin, ovotransferrin, ovomucoid, ovomucin, and lysozyme.
These make up 10% of the egg white, the remainder is water.
Many processed food depend on egg white foam for a light and airy
texture. When egg
white is whipped, the proteins get denatured and unfold into polypeptide
strands. These strands have hydrophilic as well as a hydrophobic areas,
which causes the strands to line up in a network that orients itself on
one side towards the water dropplets that are produced by the whipping
action, and on the other side orients itself towards the air bubbles,
which are also incorporated into the whipped egg white. This forms a
very thin, protective protein layer around the air bubbles, which get
trapped in the foam. Once the proteins start resuming their original
state by forming new bonds, the trapped air gets released and the foam
structure collapses.
As this process highly depends on the orientation of the hydrophilic
and hydrophobe protein strands, anything that stops this network from
forming, also disrupts foam formation. This can e.g. fats, which is e.g
found in egg yolk. This is the reason why egg white can't be beaten into
a foam, if some egg yolk accidentily ended up in the egg white, or the
utensils used for beating the egg white are greasy.
