Studies on Bitter Peptides from Casein Hydrolyzate. XIV. Bitter Taste of Synthetic Analogs of Octapeptide, Arg–Gly–Pro–Phe–Pro–Ile–Ile–Val, Corresponding to the C-Terminal Portion of β-Casein

In order to elucidate the relationship between the chemical structure and bitter taste of the C-terminal portion of β-casein, some analogues, in which the phenylalanine residue was substituted by d-phenylalanine, lysine, glycine, glutamic acid or l-pyrenylalanine, were synthesized. Sensory analyses and CD spectra showed that the location of a hydrophobic amino acid with the l-configuration between the two proline residues should be important for this series of peptides to produce a strong bitterness.