(+)-(S)-alapyridaine--a general taste enhancer?

N-(1-Carboxyethyl)-6-hydroxymethyl-pyridinium-3-ol inner salt (alapyridaine), recently identified in heated sugar/amino acid mixtures as well as in beef bouillon, has been shown to exhibit general taste-enhancing activities, although tasteless on its own. Differing from other taste enhancers reported so far, racemic (R/S)-alapyridaine and, to an even greater extent (+)-(S)-alapyridaine, the physiologically active enantiomer, are able to enhance more than one basic taste quality. The threshold concentrations for the sweet taste of glucose and sucrose, for the umami taste of monosodium L-glutamate (MSG) and guanosine-5'-monophosphate (GMP), as well as the salty taste of NaCl, were significantly decreased when alapyridaine was present. In contrast, perception of the bitter tastes of caffeine and L-phenylalanine, as well as of sour-tasting citric acid, was unaffected. Furthermore, alapyridaine was shown to intensify known taste synergies such as, for example, the enhancing effect of L-arginine on the salty taste of NaCl, as well as that of GMP on the umami taste of MSG. The activity of (+)-(S)-alapyridaine could be observed not only in solutions of single taste compounds, but also in more complex tastant mixtures; for example, the umami, sweet and salty taste of a solution containing MSG, sucrose, NaCl and caffeine was significantly modulated, thus indicating that alapyridaine is a general taste enhancer.