Studies on a Model of Bitter Peptides Including Arginine, Proline and Phenylalanine Residues. I. Bitter Taste of Di- and Tripeptides, and Bitterness Increase of the Model Peptides by Extension of the Peptide Chain

In order to elucidate the relationship between bitter taste and chemical structure in peptides, various kinds of model bitter peptides containing arginine, proline and phenylalanine were synthesized, and the contribution of the individual amino acids to the bitter taste was made clear. It was confirmed that, in order to strengthen the bitterness in di- and tripeptides, the hydrophobic amino acid needs to be located at the C-terminal and, conversely, the basic amino acid should be located at the N-terminal Furthermore, a strong bitter taste was observed when arginine was contiguous to proline such as Arg-Pro, Gly-Arg-Pro and Arg-Pro-Gly. A synergistic effect for bitter taste was observed in the peptides whose structure is (Arg)l-(Pro)m-(Phe)n (l=1, 2; m, n = 1 ~ 3) by increasing the number of amino acids. Among them, the octapeptide (Arg-Arg-Pro-Pro-Pro-Phe-Phe-Phe) possessed an extremely bitter taste with its threshold value of 0.002 mm and was found to be the most bitter among the peptides.