Umami

Umami, also referred to as savoriness, has been proposed as one of the basic tastes sensed by specialized receptor cells present on the human and animal tongue. Umami (旨味) is a loanword from Japanese meaning "good flavor" or "good taste" (noun). In English, however, "brothy", "meaty", or "savory" have been proposed as alternative translations. Inasmuch as it describes the flavor common to savory products such as meat, cheese, and mushrooms, umami is similar to Brillat-Savarin's concept of osmazome, an early attempt to describe the main flavoring component of meat as extracted in the process of making stock.

The umami taste is due to the detection of the carboxylate anion of glutamic acid, a naturally occurring amino acid common in meat, cheese, broth, stock, and other protein-heavy foods. Salts of glutamic acid, known as glutamates, easily ionize to give the same carboxylate form and therefore the same taste. For this reason, they are used as flavor enhancers. The most commonly used of these is monosodium glutamate (MSG). While the umami taste is due to glutamates, 5'-ribonucleotides such as guanosine monophosphate (GMP) and inosine monophosphate (IMP) greatly enhance its perceived intensity. Since these ribonucleotides are also acids, their salts are sometimes added together with glutamates to obtain a synergistic flavor enhancement effect.

Excitatory substances
Umami as a separate taste was first identified in 1908 by Kikunae Ikeda of the Tokyo Imperial University while researching the strong flavor in seaweed broth. Ikeda isolated monosodium glutamate (MSG) as the chemical responsible and, with the help of the Ajinomoto company, began commercial distribution of MSG products.

Glutamate has a long history in cooking. It is naturally found in East and Southeast Asian foods, such as soy sauce and fish sauce, and in Italian foods like parmesan cheese, anchovies and ripe tomatoes. It is also prevalent in seafood, such as lobster, crabs, and shrimp.

Taste receptors
Umami has been described in biochemical studies identifying the actual taste receptor responsible for the sense of umami, a modified form of mGluR4 named "taste-mGluR4."

Umami tastes are initiated by these specialized receptors, with subsequent steps involving secretion of neurotransmitters including serotonin. Other evidence indicates guanosine derivatives may interact with and boost the initial umami signal.

Cells responding to umami taste stimuli do not possess typical synapses, but instead secrete the neurotransmitter ATP in a mechanism exciting sensory fibers that convey taste signals to the brain.

In monkey studies, most umami signals from taste buds excite neurons in the orbitofrontal cortex of the brain, showing spatially specific characteristics:
 * Single neurons having vigorous responses to sodium glutamate also respond to glutamic acid
 * Some neurons display a mechanism of satiety, indicating a process by which taste receptors in the mouth may interact with cortical neurons to curtail eating

The stomach can "taste" sodium glutamate using glumate receptors and this information is passed to the lateral hypothalamus and limbic system in the brain as a palatability signal through the vagus nerve.