Umami Taste Enhancement of MSG/NaCl Mixtures by Subthreshold L-(alpha)-Aromatic Amino Acids

l-Phenylalanine (l-Phe) and l-tyrosine (l-Tyr) are L-(alpha)-aromatic amino acids that have recently been discovered to be important components of the savory fractions of soy sauce in addition to l-glutamate. Their effects are evaluated on the umami or savory taste of monosodium L-glutamate (MSG), with or without sodium chloride (NaCl). Because l-Phe at subthreshold concentration (1.0 mM) significantly enhances an umami taste of a MSG/NaCl mixture (P = 0.000), combinations of 4 subthreshold concentrations (0, 0.5, 1.5, and 5.0 mM) of l-Phe with a weakly suprathreshold MSG (4.0 mM) and NaCl (80 mM) mixture were then rated for salty and umami intensities relative to those of standard solutions. L-Phe was found to significantly enhance the umami tastes of the MSG/NaCl mixtures when it was added in a concentration range of 0.5 to 5.0 mM (P = 0.000). However, neither the umami taste of MSG alone nor the salty taste of NaCl alone was intensified. In a further experiment, l-Tyr at the 3 subthreshold concentrations (0, 0.5, and 1.5 mM) studied was shown to have the same activity as L-Phe. The phenomenon of umami or savory enhancement by subthreshold aromatic amino acids in the soy sauce system has been established.