Foundational Concepts in Neuroscience by David E. Presti

Author:David E. Presti
Language: eng
Format: epub
Publisher: W. W. Norton & Company

Another example of pungency in foods, similar to the hot spicy pungency of chili and of black pepper, but not the same, is the pungency of mustard, horseradish, and wasabi. Associated with this particular perceptual quality of hotness is a family of molecules, the isothiocyanates, characterized by a particular configuration of sulfur, carbon, and nitrogen atoms. Allyl isothiocyanate is found in mustard and horseradish.

Another type of ionotropic Ca++ channel, called TRPA1, is activated by the binding of isothiocyanates. Activation of the TRPA1 receptors results in neural signals from a different set of cells than would be the case with capsaicin and TRPV1, and this is associated with a qualitatively different experience of hotness and pungency.

TRP-type channel proteins turn out to be all over the place in the body: in the mouth, where they are associated with the perception of spicy and pungent hotness and with minty coolness; within the skin, where they are involved in the perception of temperature and also of touch and pain (see Chapter 16); and elsewhere in the nervous system, where they are likely involved in neural signaling in yet to be discovered ways. TRP channels are another example of how when life comes up with a structure possessing useful properties, it gets slightly tweaked and modified this way and that and used over and over again in many different locations in many different, though often related, ways.

What we call flavor is a combination of several different channels of sensory information. The mouth components of taste and pungency are hugely important to the flavor of food and drink: salty, sour, sweet, bitter, umami, cool, and several kinds of spicy hot—and a few more, like the tingling of Sichuan pepper (genus Zanthoxylum) and the “fatty taste” of fatty foods. Texture, how food “feels” in the mouth, also contributes to flavor. And perhaps most important to flavor are aromatic molecules, sensed via the olfactory system. As air from our mouth is drawn back into the throat, it carries aromatic molecules from whatever we are eating or drinking up into our nasal passages from the inside, the back way. In this manner, we are always smelling what we are eating and drinking.

The aromatic qualities of food and drink are legion; thousands of different molecules activating 350 different olfactory receptors in thousands of different combinations, giving rise to a vast spectrum of subtle olfactory perceptions of great nuance and complexity. Spices, wines, and distilled liquors (such as gin, whiskey, brandy, absinthe, and many others), for example, are all defined largely by their aromatic qualities. Flavor is infinitely interesting and immensely enjoyable.

Everyone is familiar with what happens to the flavor of food and drink when we have congestion as a result of a cold. Food is said to “taste” flat and uninteresting. However, taste perception is actually working just fine. If you pay careful attention, you will find that all the tastes of salt, sour, sweet, bitter, and umami are still there. So is the hotness of chili or mustard and the coolness of mint.

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