Acid-stable amino acids are those that quantitatively survive protein hydrolysis with 6N HCl under high vacuum. This method determines such amino acid contents in pure proteins, protein isolates, protein concentrates, protein-containing foods with fat contents less than 10%, and defatted protein-containing foods. Amino acids measured include: proline (PRO), glycine (GLY), alanine (ALA), valine (VAL), isoleucine (ILE), leucine (LEU), tyrosine (TYR), phenylalanine (PHE), lysine (LYS), histidine (HIS), arginine (ARG), and ammonia (AMM).