| Summary: | Kokumi taste substances exemplified by g-glutamyl peptides and Maillard Peptides modulate salt and umami tastes. However, the underlying mechanism for their action has not been delineated. Here, we investigated the effects of a kokumi taste active and inactive peptide fraction (500-10,000 Da) isolated from mature (FII<sub>m</sub>) and immature (FII<sub>im</sub>) Ganjang, a typical Korean soy sauce, on salt and umami taste responses in humans and rodents. Only FII<sub>m</sub> (0.1–1.0%) produced a biphasic effect in rat chorda tympani (CT) taste nerve responses to lingual stimulation with 100 mM NaCl + 5 mM benzamil, a specific epithelial Na<sup>+</sup> channel blocker. Both elevated temperature (42 °C) and FII<sub>m</sub> produced synergistic effects on the NaCl + benzamil CT response. At 0.5% FII<sub>m</sub> produced the maximum increase in rat CT response to NaCl + benzamil, and enhanced salt taste intensity in human subjects. At 2.5% FII<sub>m</sub> enhanced rat CT response to glutamate that was equivalent to the enhancement observed with 1 mM IMP. In human subjects, 0.3% FII<sub>m</sub> produced enhancement of umami taste. These results suggest that FII<sub>m</sub> modulates amiloride-insensitive salt taste and umami taste at different concentration ranges in rats and humans.
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