A Sport Fitness Nutrition:  BCAA is a complex comprised of three amino acids:

Isoleucine, leucine and Valine – the important ingredients of protein. The body is incapable of producing these amino acids, and they must be absorbed from food. The three amino acids are united in a complex, since they operate together and mutually complement one another.
Peptides are molecules consisting of two or more amino acids, which are joined to one another by a peptide bond. They can be produced naturally or artificially. The short-chain AGAA Peptide is a muscle peptide.