Re: Why do salts (NaCl, KCl, MSG etc.) enhance the flavors in food?

This question is well outside of my area of expertise, so I called upon a 
colleague (Dr. Susan Cuppett, Department of Food Science and Technology, 
University of Nebraska - Lincoln) who specializes in sensory.  He response 
is shown below.

Wow - a question for the ages. The role of flavor enhancers other than 
salt has been theorized and models have been developed. These compounds 
have structure activity in that they must have a specific configuration 
and some of this involves being in 2 planes to be active - this is weird 
stuff - anyway the main theories that have held up is that 1) they act to 
activate specific receptors that when activated allow a better fit of the 
flavor they are complimenting or 2) they act to increase the time the 
primary flavor spends on its specific site. Flavor enhancement per se only 
relates to sweet, salt, sour and bitter - but we perceive it as the whole 
food. 

The role of salt is less defined, as I recall, and how the four primary 
flavors act to compliment is not well defined. But since all four do 
activivate specific mechanisms their action is related. Sweet and bitter's 
activity occurs on the surface of the taste buds while sour and salt 
elicit their response after they have transported into the taste bud cell. 
All of them eventually trigger an ionic cascade (potassium ion ) that 
eventually triggers the nerve response. Salt could very well function in 
enhancing the ionic cascade but I have not seen that in the literature. 

hope this helps. 

Susan L. Cuppett, Ph.D.