Upon baking, the protein in egg white coagulates to provide structure. Beaten eggs incorporate air in tiny cells or bubbles in the batter; this trap air expands when heated and aids in leavening.
However, egg proteins are not strong as a gluten network. They coagulated at a lower temperature, so they hold the dough in place until the proteins in the gluten have a chance to set.
Adding egg whites to batter provides structure to the finished product and that is easily broken without excessive crumbling.
In order to help leaven baked goods, add an extra half teaspoon egg free baking powder for each egg called for in recipe, along with another egg substitute to bind or thicken.
Few functions of eggs in baked products including: providing structure/is a toughener. It helps with leavening through aeration and added moisture.
The fat in egg yolks acts as a shortening. This is an important function in products that are low in other fats.
Other functions are that eggs contributing flavor and contributing color. Eggs brown easily and contribute to crust color. Eggs also adding nutritional value to the baked goods.
Egg yolks contain natural emulsifiers that help produce smooth batter. This action contributes to volume and to texture.