Bitter Taste of Synthetic C-Terminal Tetradecapeptide of Bovine β-Casein, H-Pro¹⁹⁶-Val-Leu-Gly-Pro-Val-Arg-Gly-Pro-Phe-Pro-Ile-Ile-Val²⁰⁹-OH, and Its Related Peptides

抄録

The primary structure of bovine β-casein contains the partial sequence of-Pro¹⁹⁶-Val-Leu-Gly-Pro-Val-Arg-Gly-Pro-Phe-Pro-Ile-Ile-Val²⁰⁹ in the C-terminal portion. We previously reported that the synthetic C-terminal octapeptide, Arg²⁰²-Val²⁰⁹, is extremely bitter with its threshold value 0.004 mM, 250 times as strong as that of caffeine. To further investigate the bitter taste of the C-terminal portion of β-casein, we synthesized the C-terminal tetradecapeptide, Pro¹⁹⁶-Val²⁰⁹, and some of its fragments. A hydrophobic hexapeptide, Pro¹⁹⁶-Va²⁰¹, was twice as bitter as caffeine. The bitter taste of the decapeptide, Pro²⁰⁰-Val²⁰⁹, was the same as that of Arg²⁰²-Val²⁰⁹. Although the tetradecapeptide, Pro¹⁹⁶-Val²⁰⁹, was composed of two bitter peptides, Pro¹⁹⁶-Val²⁰¹ and Arg²⁰²-Val²⁰⁹, its bitter taste was weaker than that of Arg²⁰²-Val²⁰⁹ and its threshold value was 0.015 mM. We suggested that the increase of bitterness in peptides through the introduction of hydrophobic amino acids depended on the number of hydrophobic amino acids added. In addition, the synthetic retro analog of Arg²⁰²-Val²⁰⁹ (H-Val-Ile-Ile-Pro-Phe-Pro-Gly-Arg-OH) was not as bitter as Arg²⁰²-Val²⁰⁹. This indicated that the sequence of Arg²⁰²-Val²⁰⁹ is important for extreme bitterness.