Development and genetics of glutamate taste preference.
The sodium salt of glutamic acid, monosodium glutamate (MSG), and certain other amino acids and ribonucleotides impart a unique taste sensation often called 'umami.' We have been studying preference for umami substances in two systems: inbred mice and human infants. In 48-hr tests, C57BL/6J (C57) mice exhibit a lower preference threshold for MSG than do 129/J mice. Moreover, C57 mice show a greater preference across a wide range of concentrations and, at high (e.g., 300-600 mM) concentrations, consume greater amounts of MSG. To examine whether the strain difference in MSG preference might be related to a similar strain difference in preference for sucrose and other sweeteners, as might be suggested from studies with rats, preferences for MSG and sucrose in the second (F2) generation were examined. Preferences for sucrose and for MSG were not positively correlated in the F2 indicating that these strain differences depend on different genes. For human adults, unlike mice, the taste of aqueous MSG is not palatable. Our studies of human infants also indicate that MSG alone is not preferred to plain water, but, when it is added to soup, the soup plus MSG is preferred to soup alone. Ongoing studies are designed to determine whether simple mixtures of MSG with other tastants, in particular NaCl, are preferred to water alone, NaCl alone, and MSG alone.