Tasting > Organoleptic characteristics > Tast
It is possible to distinguish four main characteristics of taste: savoury, sweet, sour (or acidic) and bitter.
Taste is stimulated initially by the contact of a watery solution of chemical compounds with the taste buds of the tongue, soft palate, and pharynx, epiglottis and the mucous membrane of the cheek. Therefore saliva plays an important role in tasting, as it dissolves or dilutes the sapid molecules (of taste) and transports them to the taste receptors. Inside the mouth there is a hierarchy of sensory receptors.
At the lowest level there is the epithelium of the mouth cavity, which is covered in papilla. On a higher level there are structures with varying forms, which contain the taste buds. There are four kinds of papilla with different sensory meaning: fungiform, filiform, circumvallated and foliate. The papilla contain varying numbers of taste buds and are situated in different parts of the tongue. The greatest sensitivity to the four basic flavours is not uniformly distributed on the tongue: acidic (on the side), savoury (side and internal tip), sweet (internal tip) and bitter (back); all the other flavours defined as complex can be said to be made up of a combination of two or more basic flavours, influenced by smell, heat and mechanic factors.
TASTE BUDS AND PAPILLAE OF THE TONGUE
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1. pore
2. epithelium cells
3. microvilli
4. taste cells
5. synapsis
6. perigemmal buds
7. basal cells
8. support cells
9. nerve fibres
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I. fungiform papillae
II. filiform papillae
III. foliate papillae
IV. vallate papillae
V. buttons on tongue base
1. sweet
2. salt
3. sour/acidic
4. bitter |
1. foliate papillae
2. filiform papillae
3. vallate papillae
4. fungiform papillae
5. taste buds and synapsis
6. nerve fibres
7. striated muscolature
8. salivary glands |
The taste buds are deep in the epithelium of the papilla; adults have about two thousand taste buds; it is thought that new born babies have about ten thousand.
Inside taste buds are sensory receptor cells, the cells of support to the basic cells. The main function of sensory cells, innervated by nervous fibres, is to link taste molecules and initiate the primary sensory process. When a taste molecule arrives on a sensory receptor cell, the permeability of its membrane is influenced. The polarity of the membrane changes as there is a flow of Na ions from the outside to the inside. This causes a potential energy, which is transported along the three cranial nerves (VII, IX X pair) to the brain. The frequency and duration of the discharge are proportionate to the concentration of the substance.
With regard to organoleptic recognition of stimuli, it has not yet been completely clarified whether specific receptors exist for the perception of one single type of flavour.
The differentiation of the stimulus is mainly due to the differences in the link which establishes itself between the molecule and receptor, but this is true only for molecules which have a P.M. of below 300; if above 300, the response becomes simply astringent. This is due to the large number of molecules and the precipitation of ptyalin.
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