Role of the Hydrophobic Amino Acid Residue in the Bitterness of Peptides

In order to investigate the role of the side chain of amino acids in the bitterness in peptide, someioligopeptides containing glycine, alanine, aminobutyric acid, valine, isoleucine, norvaline (n-Val) and norleucine (n-Leu) were synthesized and their tastes were evaluated. For the bitter taste to be exhibited, the side chain skeleton of the amino acid should consist of at least three carbons. The peptides consisting of amino acids having a side chain of less than three carbons did not exhibit bitterness, while the peptides consisting of amino acids having a side chain of more than three carbons did exhibit bitterness. Valine exhibited an intermediate feature, the taste of valine peptides varying dependent upon the structure. The difference of the branching structure in side chains was less concerned with peptide bitterness.