Monday, November 7
TASTE
TASTE
is one of the traditional five senses. It refers to the capability to detect
the taste of substances such as food, certain minerals, and poisons, etc
The sense of taste is often confused with the "sense" of
flavor, which is a combination of taste and smell perception. Flavor depends on
odor, texture, and temperature as well as on taste. Humans receive tastes
through sensory organs called taste
buds, or gustatory calyculi,
concentrated on the upper surface of the tongue. There are five basic tastes: Sweet, Bitter, Sour, Salty and Umami.
Other tastes such as calcium and free fatty acids may be other basic tastes but
have yet to receive widespread acceptance.
- Basic Tastes -
For a long period, it was commonly accepted that there is a finite
and small number of "basic tastes" of which all seemingly complex
tastes are ultimately composed. Just as with primary colors, the
"basic" quality of those sensations derives chiefly from the nature
of human perception, in this case the different sorts of tastes the human
tongue can identify. As of the early twentieth century, physiologists and
psychologists believed there were four basic tastes: sweetness, sourness, saltiness, bitterness. At that time umami was not proposed as a fifth taste[19] but now a
large number of authorities recognize it as the fifth taste.[citation needed]
In Asian countries within the sphere of mainly Chinese and Indian cultural
influence, pungency (piquancy or hotness) had traditionally been considered a
sixth basic taste.
Sweetness
Sweetness, usually regarded as a pleasurable sensation, is
produced by the presence of sugars and a few other substances. Sweetness is
often connected to aldehydes and ketones, which contain a carbonyl group. Sweetness is detected by a variety
of G protein coupled receptors coupled to the G protein gustducin found on the taste buds. At least two
different variants of the "sweetness receptors" must be activated for
the brain to register sweetness. Compounds the brain senses as sweet are thus compounds
that can bind with varying bond strength to two different sweetness receptors. The
average human detection threshold for sucrose is 10 millimoles per liter.
Sourness
Sourness is the taste that detects acidity. The sourness of
substances is rated relative to dilute hydrochloric acid, which has a sourness
index of 1. By comparison, tartaric acid has a sourness index of 0.7, citric acid
an index of 0.46, and carbonic acid an index of 0.06.
Sour taste is detected by a small subset of cells that are
distributed across all taste buds in the tongue. Sour taste cells can be
identified by expression of the protein , although this gene is not required
for sour responses. There is evidence that the protons that are abundant in
sour substances can directly enter the sour taste cells. This transfer of
positive charge into the cell can itself trigger an electrical response. It has
also been proposed that weak acids such as acetic acid, which are not fully
dissociated at physiological pH values, can penetrate taste cells and thereby
elicit an electrical response. According to this mechanism, intracellular
hydrogen ions inhibit potassium channels, which normally function to
hyperpolarize the cell. By a combination of direct intake of hydrogen ions
(which itself depolarizes the cell) and the inhibition of the hyperpolarizing
channel, sourness causes the taste cell to fire action potentials and release
neurotransmitter. The mechanism by which animals detect sour is still not
completely understood.
Saltiness
Saltiness is a taste produced primarily by the presence of sodium
ions. Other ions of the alkali metals group also taste salty, but the further
from sodium the less salty the sensation is.
Bitterness
Bitterness is the most sensitive of the tastes, and many perceive
it as unpleasant, sharp, or disagreeable, but it is sometimes desirable and
intentionally added via various bitterness agents. Common bitter foods and
beverages include coffee, unsweetened cocoa, South American mate, bitter gourd,
beer (due to hops), bitters, olives, citrus peel, dandelion greens, wild
chicory, and escarole. Quinine is also known for its bitter taste and is found
in tonic water.
Umami
Umami is an appetitive taste and is described as a savory or meaty
taste. It can be tasted in cheese and soy sauce, and while also found in many
other fermented and aged foods, this taste is also present in tomatoes, grains,
and beans.
Reference:
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