A substance’s taste is produced when it reacts chemically to taste receptors (TRCs), located on taste buds, primarily in the mouth. The sensory system includes five senses, including taste. All organisms rely on taste perception as a major sensory input. Taste receptors are receptors that help to facilitate the sensation of taste. The taste receptors are on the membranes. The gustatory sense of mammals includes five basic flavors: sweet, bitter and salty.
In common speech, “taste”, or sensations from the mouth cavity, are often described as “taste”. But the biological definition is much narrower, and it only covers sensations transmitted by a specially defined anatomically-physiological chemosensorygustatory system. Food can also evoke other senses such as odor, temperature, touch and irritation. The non-gustatory components of food are perceived by different systems – olfaction and somatic sensation.
Animals use taste receptors to evaluate food. The sense is a powerful tool that can trigger a variety of reactions, from the innate behavioral responses such as attraction and repulsion to food to the joy of eating. Notably, one taste receptor expresses many different taste receptors proteins.
This indicates that each cell can recognize multiple tastes. Taste perception is also important for interoceptive (hunger and safety signals) and exteroceptive (vision, smell, and somatosensation), as well as generating behavioral responses.
Taste receptors protect the organism by preventing poisonous compounds from entering. Also, reports from recent years suggest that the proteins have functions other than detecting tastes. Airway smooth muscle tissue contains human taste receptors. Tastants and their effects on human bronchi are currently being investigated.
In mammals, the gustatory system includes taste receptors organized within taste buds that are located in gustatory papillae. Most taste papillae, which are divided into three different types — fungiforms, foliates, and vallates — are located on the tongue. A large number of taste papillae are located in non-lingual areas such as the oropharynx and larynx. TRCs have apical end exposed to the mouth and they react with water-soluble chemicals as taste stimuli. This interaction generates signals, which are then transmitted to the cerebral cortex via three branches of cranial nervous system: VII (facial),IX (glossopharyngeal),and X(vagus).
During the past few years, there have been tremendous advances in the discovery, characterization, and understanding of the taste receptors found in vertebrates. These receptors recognize sweet, umami, and bitter stimuli. Allelic variants found in the T1R/T2R gene can explain individual differences of taste in certain situations.
All animals depend on nutrients to survive. Toxic substances are often found in the sources of nutrition. Taste helps animals determine whether the food they are eating is healthy or harmful. Taste evolved probably to help animals select food that is appropriate for their body.
Currently, taste sensations of humans are classified into five different categories: salty, sweet (umami), bitter, sour and umami. Foods that have a bitter, aversive taste can often be toxic. Sour and bitter tastes are also signs of spoiled foods. Salts are the main stimuli for salty tastes, but other salts can also produce a salty flavor.
Salty tastes are a sign of mineral or sodium content. Sugars are the most common sweet taste stimuli, and they indicate that carbohydrates are present in food. L-glutamate has the highest umami content, which could indicate protein. The taste of lipids and calcium is also important, but there are some doubts about whether they have a similar flavor.
The existence and variety of taste qualities suggests that taste has a unique coding mechanism. This is done by special taste receptors. This hypothesis is supported by current data. Humans are able to taste bitterness, umami, or sweetness by using proteins in the T1R/T2R families. Salty and sour taste receptors are candidates.
Practical Applications of Taste ReceptorsThere’s a lot of interest in the development and modification taste receptors and stimuli for humans and animals. Food and drink can be made healthier without sacrificing the taste and patients are more likely to accept oral medication. A large market exists for artificial sweeteners and umamis, taste enhancers that increase the sweetness, umami and saltiness of food, bitterness blockers and pharmaceutical compounds.
A demand exists for the development of non-lethal repellents against wild animals (e.g. non-toxic chemical compounds with an aversive flavour). Lack of knowledge about the molecular identities of taste receptors has hampered the development of these products. The discovery of taste receptors will help to design novel taste-active compounds.
Allelic variations of taste receptors in humans can influence food perception, consumption, and choice. In turn, this can influence the nutrition of individuals and possibly predispose them to certain illnesses. Some alleles for taste receptors could be risk factors for disease. Genotypes are useful for identifying disease risk factors and recommending interventions. Some data are available to illustrate the role that taste receptors play in human health and nutrition. Alleles sensitive of the TAS2R38 human receptor are activated by PTC and PROP compounds that contain an N-C=S moiety.
Some plants humans consume contain compounds called glucosinolates. They also contain thiourea. A recent study has shown that TAS2R38 genotype affects the perception of the bitterness of glucosinolate-containing plants, such as broccoli, turnip, and horseradish. Allelic variation TAS2R38 can have a much wider effect on the food preference of children. A biomarker that could indicate alcoholism is the variation in taste receptors.
Ethanol has both bitter and sweetness components. Bachmanov’s et. al. (2003) report that variation in the sweet and bitter taste response is associated with ethanol consumption and perception. Bachmanov et.al., 2002, found that mice with allelic variations of the Tas1r3 sugar taste receptor gene were more likely to consume ethanol. The genes that are responsible for the association between hedonic responses and sweet taste in humans are unknown. The higher sensitivity of the ethanol bitterness could protect against excessive consumption.
Taste receptors serve as a link between the inner and outer worlds. In the last few years, the discovery and understanding of T1R/T2R receptors has made tremendous progress.