Studies of Bitter Peptides from Casein Hydrolyzate. III. Bitter Taste of Synthetic Analogs of BPIa (Arg–Gly–Pro–Pro–Phe–Ile–Val) Containing d -Proline or Glycine in Place of l -Proline

In order to elucidate the relationship between chemical structure and bitter taste of BPIa, the analogs containing d-proline or glycine in place of the l-proline in the 3- or 4-positions were synthesized. The bitter taste of [d-Pro3,4]–BPIa (ld-d), [d-Pro3]–des–Pro3–BPIa (2d), and [Gly3]–des–Pro3–BPIa lacking the l-proline residue was much weaker than that of the peptides containing the l-proline, BPIa (1l-l), 1l-d, 1d-l, and 2l. The CD curves of these analogs and BPIa were measured in water. The results suggested that the bitter taste of BPIa is caused by the spatial structure attributed to the l-proline residue.