There are two values that are used to help determine the quality of protein in a product:
Protein Digestibility Corrected Amino Acid Score or the PDCAA - this determines how complete a protein is. 1 is the highest score possible and egg whites come in on top with a perfect score in the method.
Biological Value - the biological value measure the amount of protein that is retain when the protein is absorbed. Egg protein is the leader in this measure and comes in with a score of 100 of biological value. This means that the egg protein contains every one of the essential amino acids that are bodies need.