Some taste physiologists argue that the basic-four list of tastes (sweet, sour, salty and bitter) should be expanded to include umami (a Japanese term pronounced oo-mom-ee). Some laboratory research supports their view. Other experts demur, believing that the jury is still out. They say that the umami taste may not be a basic taste. It could be, for instance, a side effect of a chemical reaction triggered by glutamate, an amino acid (a building block of protein). When glutamate is in its free form (that is, not combined with other amino acids), it could chemically modify the performance of the sweet, sour, salty, or bitter taste receptors, creating the illusion of a new basic taste.
Whether umami is a basic taste of not, it is real and has an identifiable flavor profile, though it is difficult to characterize in words. It has been variously described as "savory", "brothy", and "meaty". These terms cover too broad a taste spectrum to communicate adequately the umami taste profile to anyone who does not already know it. Fortunately, monosodium glutamate is a salt form of glutamate and does produce an umami taste.
** Asian Recipes