Actually heat does denature protein
Unfortunately cooking does cause some of the protein to be lost. It is unfortunate but true thats why whey protein manufactures would advertise cold ion exchange and stuff because heat would cause protein to be lost. You would get more protein from a raw egg than a cooked one, but you could get salmenella as well.
As for the lime juice thats bull shit. Citric acid would not destroy the protein. If that were true then your gastric juices would render all meat useless.