Taste is high on the list as a selection criteria for food. Taste buds – so named because the arrangement of their cells is similar to the shape of a flower – are located primarily on the tongue, but are also found on the hard and soft palates of the mouth and in the pharynx. Most of the taste bud papillae are found on the underside, the sides, and the tip of the tongue, while there are none on the flat, central surface of the tongue. Many tasted substances are a combination of non-volatile and volatile compounds. In order for a substance to be tasted, it must dissolve in liquid or saliva, which is 99.5 percent water. In the middle of each taste bud is a pore, similar to a little pool, where saliva collects. When food comes into the mouth, bits of it are dissolved in the saliva pools and they come into contact with the cilia, small hair-like projections from the gustatory cells.
The gustatory cells relay a message to the brain via one of the cranial nerves (facial, vagus, and gloss pharyngeal). The brain, in turn, translates the nervous electrical impulses into a sensation people recognize as “taste”. As people age, the original 9,000 to 10,000 taste bugs begin to diminish in number, so that people over 45 often find themselves using more salt, spices, and sugar in their food. Another factor influencing the ability of a person to taste is the degree to which a compound can dissolve. The amount of molecules in a solution that will spread over the tongue depends on their size and surrounding moisture content.
The Four Taste Stimuli
Different areas on the tongue are associated with the four basic types of taste: sweet, sour, bitter and salty. The tip is more sensitive to sweet and sour, the sides to salty and sour, and the back to bitter sensations. The time it takes to detect each of these taste stimuli varies from a split second for salt to a full second for bitter substances. Bitter tastes, therefore, have a tendency to linger.
The chemical basis of these four categories of taste is described below:
- The sweetness of sugar comes form the chemical configuration of its molecule.
- Sour taste is related to the concentration of hydrogen ions, which are found in the natural acids of fruits, vinegar, and certain vegetables.
- Bitterness is imparted by compounds such as caffeine (tea, coffee), theo bromine (chocolate) and phenolic compounds (grapefruit).
- Salty taste comes from salt ions in dosium chloride (NaCI) or other salts found naturally in some foods.