Gustation

Gustation, the sense of taste, works together with olfaction to perceive flavor. For taste to occur, a stimulus must first dissolve in saliva and be distributed throughout the papillae of the tongue. Most types of papillae contain taste buds, which are bundles of sensory cells innervated by branches of the cranial nerves.

With a salted chocolate caramel, saltiness and even sourness are perceived because the sensory cells contain ion channels. For example, sodium, from the salt, passes through sodium channels found on one cell type, and initiates an action potential in the cell. The action potential travels down the sensory cell and passes to a nerve. The nerve relays the taste information to the thalamus, and then the gustatory cortex in the brain, where the flavors are experienced.

When more of the caramel dissolves, sweetness, savoriness and even bitterness are perceived. These tastes come from different complex compounds binding to the chemoreceptors, which are G-protein coupled receptors, and activating second messenger signaling mechanisms.

For instance, functional groups, such as the carbonyls in sugar, and glutamate, the amino acid found in savory flavors, bind to one family of taste receptors. Another family binds and detects over 200 different bitter molecules, like the alkaloids found in cocoa. Thus, taste receptors specific for each flavor are expressed on the same taste bud throughout the entire tongue, not entirely bound within particular regions.