Umami

Umami (旨み、旨味, うまみ) is a proposed addition to the currently accepted four basic tastes sensed by specialized receptor cells present on the human tongue. The same taste is also known as xiānwèi in Chinese cooking. Umami is a Japanese word meaning "savory" or "deliciousness" and so applies to the sensation of savoriness, specifically to the detection of the natural amino acid, glutamic acid, or glutamates common in meats, cheese and other protein-heavy foods. The action of umami receptors explains why foods treated with monosodium glutamate (MSG) often taste "heartier".

Glutamate has a long history in cooking: it appears in Asian foods such as soy sauce and fish sauce, and in Italian food in parmesan cheese and anchovies. It is the taste of Marmite in the UK, of Golden Mountain sauce in Thailand, of Maggi Sauce worldwide, of Goya Sazón on the Latin islands of the Caribbean, of Salsa Lizano in Costa Rica and of Kewpie mayonnaise in Japan. It also is directly available in monosodium glutamate.

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 (link in French), an early attempt to describe the main flavoring component of meat as extracted in the process of making stock.

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

Taste receptors
Acknowledged subjectively as a special taste by Eastern civilizations for generations, 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 adenosine triphosphate (ATP) and 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. These taste receptors are located everywhere on the tongue.

In monkey studies, most umami signals from taste buds excite neurons in the orbitofrontal cortex of the brain, showing spatially-specific characteristics:
 * There is a cortical map representation for the taste of glutamate separate from that of other taste stimuli like sweet (glucose), salt, bitter (quinine) and sour (hydrochloric acid)
 * 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
 * Umami flavor is strongest when combined with aromas (e.g., monosodium glutamate and garlic), a result leading to speculation that glutamate may stimulate umami effects by acting simultaneously with the aromas, texture and appearance of food.