Complex sentence: Silk amino acids (SAAs) are just that, amino acids in the form of peptides rather than individual amino acids which are produced by hydrolzying (or breaking apart) silk proteins into smaller peptide chains, typically 18 to 19 amino acids in length.
Split into simpler sentences: Silk amino acids (SAAs) are comprised of peptides, rather than individual amino acids. The way silk amino acids are made is by hydrolyzing, or breaking apart, the silk protein, into smaller peptide chains which typically are 18 to 19 amino acids in length.