Egg white entraps air when it is beaten
Oil and water mixed together will form an emulsion.
Egg white coagualates (sets) at 60'C and yolk at 70'C, so when these temperatures are reached, it sets and stays thickened.
Coagulation sticks the ingredients together as they cook.
During baking, the egg glaze turns the pastry golden brown.
Foods are brushed with egg and then dipped in breadcrumbs e.g fried fishcakes.