Aftertaste
Encyclopedia
Aftertaste is the taste
intensity of a food
or beverage
that is perceived immediately after that food or beverage is removed from the mouth. The aftertastes of different foods and beverages can vary by intensity and over time, but the unifying feature of aftertaste is that it is perceived after a food or beverage is either swallowed or spat out. The neurobiological
mechanisms of taste (and aftertaste) signal transduction
from the taste receptors in the mouth to the brain have not been elucidated completely. Recently, the primary taste processing area located in the insula
has been observed to be involved in aftertaste perception.
Because taste perception is unique to every person, descriptors for taste quality and intensity have been standardized, particularly for use in scientific studies. For taste quality, foods can be described by the commonly used terms ‘‘sweet’’, ‘‘sour’’, ‘‘salty’’, ‘‘bitter’’, "umami", or “no taste”. Description of aftertaste perception relies heavily upon the use of these words to convey the taste that is being sensed after a food has been removed from the mouth.
The description of taste intensity is also subject to variability among individuals. Variations of the Borg Category Ratio Scale
or other similar metrics are oftentimes used to assess the intensities of foods. The scales typically have categories that range from either zero or one through ten (or sometimes beyond ten) that describe the taste intensity of a food. A score of zero or one would correspond to unnoticeable or weak taste intensities, while a higher score would correspond to moderate or strong taste intensities. It is the prolonged moderate or strong taste intensities that persist even after a food is no longer present in the mouth that describe aftertaste sensation.
Foods that have distinct aftertastes are distinguished by their temporal profiles, or how long their tastes are perceived during and after consumption. A sample testing procedure to measure a food’s temporal profile would entail first recording the time of onset for initial taste perception when the food is consumed, and then recording the time at which no there is no longer any perceived taste. The difference between these two values yields the total time of taste perception. Match this with intensity assessments over the same time interval and a representation of the food’s taste intensity over time can be obtained. With respect to aftertaste, this type of testing would have to measure the onset of taste perception from the point after which the food was removed from the mouth.
or “nontasters”
based on their sensitivity to the bitterness of propylthiouracil
and the expression of fungiform papillae on their tongues has suggested that the variations from person-to-person observed in taste perception are genetically based. If so, then sensations of aftertaste could also be affected by the activities of specific genes that affect an individual’s perception of different foods. For example, the intensity of the aftertaste sensations "nontasters" experienced after caffeine consumption was found to diminish faster than the sensations "tasters" experienced. This may imply that because of their taste bud profiles, "tasters" may be more sensitive to the tastes of different foods, and thus experience a more persistent sensation of those foods’ tastes.
In the context of aftertaste, the combination of both receptor-dependent and receptor-independent processes have been proposed to explain the signal transduction mechanisms for foods with distinct aftertastes, particularly those that are bitter. The receptor-dependent process is the same as what was described above. However, the receptor-independent process involves the diffusion of bitter, amphiphilic chemicals like quinine
across the taste receptor cell membranes. Once inside the taste receptor cell, these compounds have been observed to activate intracellular G-proteins
and other proteins that are involved in signaling pathways routed to the brain. The bitter compounds thus activate both the taste receptors on the cell surface, as well as the signaling pathway proteins in the intracellular space. Intracellular signaling may be slower than taste cell receptor activation since more time is necessary for the bitter compounds to diffuse across the cell membrane and interact with intracellular proteins. This delayed activation of intracellular signaling proteins in response to the bitter compounds, in addition to the extracellular receptor signaling is proposed to be related to the lingering aftertaste associated with bitter foods. The combination of both mechanisms leads to an overall longer response of the taste receptor cells to the bitter foods, and aftertaste perception subsequently occurs.
; the nucleus of the solitary tract located in the brainstem also plays a major role in taste perception. These regions were identified when human subjects were exposed to a taste stimulus and their cerebral blood flow measured with magnetic resonance imaging
. Although these regions have been identified as the primary zones for taste processing in the brain, other cortical areas are also activated during eating, as other sensory inputs are being signaled to the cortex.
For aftertaste, much is unclear about the cortical processing related to its perception. The first neuroimaging study to evaluate the temporal taste profile of aspartame
, an artificial sweetener, in humans was published in 2009. In it, the insula was observed to be activated for a longer period of time than other sensory processing areas in the brain when the aftertaste profile of aspartame was measured. Subjects were administered a solution of aspartame for a specific amount of time before being instructed to swallow the solution. Functional magnetic resonance images of the blood flow in the subjects’ brains were recorded before and after they swallowed the aspartame solution. Before swallowing, the amygdala
, somatosensory cortex, thalamus
, and basal ganglia
were all activated. After swallowing, only the insula remained activated and the response of the other brain regions was not evident. This suggests that the insula may be a primary region for aftertaste sensation because it was activated even after the aspartame solution was no longer present in the mouth. This finding aligns with the insula’s identification as a central taste processing area and simply expands its function. An explanation for less activation of the amygdala was that because it is a reward center in the brain, less reward would be experienced by the subjects during prolonged exposure to the aspartame solution.
is an emergent property that is the combination of multiple sensory systems including olfaction
, taste, and somatosensation
. How the flavor of a food is perceived, whether it is unpleasant or satisfying, is stored as a memory so that the next time the same (or a similar) food is encountered, the previous experience can be recalled and a decision made to consume that food. This process of multisensory inputs to the brain during eating, followed by learning from eating experiences is the central idea of flavor processing.
Richard Stevenson mentions in The Psychology of Flavour that people often do not realize that a food’s flavor can be described by the food’s smell, taste, or texture. Instead, he claims, people perceive flavor as a “unitary percept”, in which a descriptor for either taste or smell is used to describe a food’s flavor. Consider the terms that are used to describe the flavors of foods. For instance, a food may taste sweet, but oftentimes its flavor is described as such while not considering its smell or other sensory characteristics. For example, honey tastes sweet so its smell is associated with that descriptor, and sweet is also used to describe its flavor. In fact, sweetness is one of the four basic taste qualities and only comprises part of a food’s flavor.
Unlike flavor, aftertaste is a solely gustatory event that is not considered to involve any of the other major senses. The distinction of being based on one (aftertaste) versus multiple (flavor) sensory inputs is what separates the two phenomena.
and acesulfame-K
are known for their bitter aftertastes. Recently, GIV3727 (4-(2,2,3-trimethylcyclopentyl) butanoic acid), a chemical that blocks saccharin and acesulfame-K activation of multiple bitter taste receptor
s has been developed. In the study, the addition of the bitter taste receptor antagonist
GIV3727 to the saccharin and acesulfame-K solutions resulted in significantly lower taste intensity ratings when compared to the solutions that were not treated with GIV3727. This suggests that GIV3727 inhibits the normal functions of the bitter taste receptors because saccharin and acesulfame-K's bitter aftertastes were not observed. The ability to inhibit activation of the bitter taste receptors can have far-reaching effects if the bitter aftertastes of not only these two artificial sweeteners but also other foods, beverages, and even pharmaceuticals can be minimized.
the aftertaste or finish of a wine, is an important part of the evaluation. After tasting a wine, a taster will determine the wine’s aftertaste, which is a major determinant of the wine’s quality. The aftertaste of a wine can be described as bitter, persistent, short, sweet, smooth, or even non-existent. Included in assessing the aftertaste of a wine is consideration of the aromas still present after swallowing. High quality wines typically have long finishes accompanied by pleasant aromas. By assessing the combination of olfactory and aftertaste sensations, wine tasting actually determines not only the aftertaste profile of a wine, but its flavor profile as well.
Taste
Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....
intensity of a food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...
or beverage
Drink
A drink, or beverage, is a liquid which is specifically prepared for human consumption. In addition to fulfilling a basic human need, beverages form part of the culture of human society.-Water:...
that is perceived immediately after that food or beverage is removed from the mouth. The aftertastes of different foods and beverages can vary by intensity and over time, but the unifying feature of aftertaste is that it is perceived after a food or beverage is either swallowed or spat out. The neurobiological
Neuroscience
Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...
mechanisms of taste (and aftertaste) signal transduction
Signal transduction
Signal transduction occurs when an extracellular signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecules creating a response...
from the taste receptors in the mouth to the brain have not been elucidated completely. Recently, the primary taste processing area located in the insula
Insular cortex
In each hemisphere of the mammalian brain the insular cortex is a portion of the cerebral cortex folded deep within the lateral sulcus between the temporal lobe and the frontal lobe. The cortical area overlying it towards the lateral surface of the brain is the operculum...
has been observed to be involved in aftertaste perception.
Temporal taste perception
Characteristics of a food’s aftertaste are quality, intensity, and duration. Quality describes the actual taste of a food and intensity conveys the magnitude of that taste. Duration describes how long a food’s aftertaste sensation lasts. Foods that have lingering aftertastes typically have long sensation durations.Because taste perception is unique to every person, descriptors for taste quality and intensity have been standardized, particularly for use in scientific studies. For taste quality, foods can be described by the commonly used terms ‘‘sweet’’, ‘‘sour’’, ‘‘salty’’, ‘‘bitter’’, "umami", or “no taste”. Description of aftertaste perception relies heavily upon the use of these words to convey the taste that is being sensed after a food has been removed from the mouth.
The description of taste intensity is also subject to variability among individuals. Variations of the Borg Category Ratio Scale
Borg scale
In sports and particularly exercise testing, the Borg RPE Scale measures perceived exertion. In medicine this is used to document the patient's exertion during a test, and sports coaches use the scale to assess the intensity of training and competition. The original scale introduced by Gunnar Borg...
or other similar metrics are oftentimes used to assess the intensities of foods. The scales typically have categories that range from either zero or one through ten (or sometimes beyond ten) that describe the taste intensity of a food. A score of zero or one would correspond to unnoticeable or weak taste intensities, while a higher score would correspond to moderate or strong taste intensities. It is the prolonged moderate or strong taste intensities that persist even after a food is no longer present in the mouth that describe aftertaste sensation.
Foods that have distinct aftertastes are distinguished by their temporal profiles, or how long their tastes are perceived during and after consumption. A sample testing procedure to measure a food’s temporal profile would entail first recording the time of onset for initial taste perception when the food is consumed, and then recording the time at which no there is no longer any perceived taste. The difference between these two values yields the total time of taste perception. Match this with intensity assessments over the same time interval and a representation of the food’s taste intensity over time can be obtained. With respect to aftertaste, this type of testing would have to measure the onset of taste perception from the point after which the food was removed from the mouth.
Variability of human taste perception
The categorization of people into “tasters”Supertaster
A supertaster is a person who experiences the sense of taste with far greater intensity than average. Women are more likely to be supertasters, as are individuals of Asian and African descent. The cause of this heightened response is currently unknown, although it is thought to be, at least in...
or “nontasters”
Supertaster
A supertaster is a person who experiences the sense of taste with far greater intensity than average. Women are more likely to be supertasters, as are individuals of Asian and African descent. The cause of this heightened response is currently unknown, although it is thought to be, at least in...
based on their sensitivity to the bitterness of propylthiouracil
Propylthiouracil
Propylthiouracil or 6-n-Propylthiouracil is a thioamide drug used to treat hyperthyroidism by decreasing the amount of thyroid hormone produced by the thyroid gland...
and the expression of fungiform papillae on their tongues has suggested that the variations from person-to-person observed in taste perception are genetically based. If so, then sensations of aftertaste could also be affected by the activities of specific genes that affect an individual’s perception of different foods. For example, the intensity of the aftertaste sensations "nontasters" experienced after caffeine consumption was found to diminish faster than the sensations "tasters" experienced. This may imply that because of their taste bud profiles, "tasters" may be more sensitive to the tastes of different foods, and thus experience a more persistent sensation of those foods’ tastes.
Taste receptor dynamics
Because a lingering taste sensation is intrinsic to aftertaste, the molecular mechanisms that underlie aftertaste are presumed to be linked to either the continued or delayed activation of receptors and signaling pathways in the mouth that are involved in taste processing. The current understanding of how a food's taste is communicated to the brain is as follows:- Chemicals in food interact with receptors on the taste receptor cellsTaste receptorA Taste receptor is a type of receptor which facilitates the sensation of taste.Examples include TAS2R16 and TAS2R38.They are divided into two families:* Type 1, sweet, first characterized in 2001: –...
located on the tongue and the roof of the mouth. These interactions can be affected by temporal and spatial factors like the time of receptor activation or the particular taste receptors that are activated (sweet, salty, bitter, etc.). - The chorda tympaniChorda tympaniThe chorda tympani is a nerve that branches from the facial nerve inside the facial canal, just before the facial nerve exits the skull via the Stylomastoid foramen...
(cranial nerve VII), the glossopharyngeal nerveGlossopharyngeal nerveThe glossopharyngeal nerve is the ninth of twelve pairs of cranial nerves . It exits the brainstem out from the sides of the upper medulla, just rostral to the vagus nerve...
(cranial nerve IX), and the vagus nerveVagus nerveThe vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
(cranial nerve X) carry information from the taste receptors to the brain for cortical processing.
In the context of aftertaste, the combination of both receptor-dependent and receptor-independent processes have been proposed to explain the signal transduction mechanisms for foods with distinct aftertastes, particularly those that are bitter. The receptor-dependent process is the same as what was described above. However, the receptor-independent process involves the diffusion of bitter, amphiphilic chemicals like quinine
Quinine
Quinine is a natural white crystalline alkaloid having antipyretic , antimalarial, analgesic , anti-inflammatory properties and a bitter taste. It is a stereoisomer of quinidine which, unlike quinine, is an anti-arrhythmic...
across the taste receptor cell membranes. Once inside the taste receptor cell, these compounds have been observed to activate intracellular G-proteins
G protein
G proteins are a family of proteins involved in transmitting chemical signals outside the cell, and causing changes inside the cell. They communicate signals from many hormones, neurotransmitters, and other signaling factors. G protein-coupled receptors are transmembrane receptors...
and other proteins that are involved in signaling pathways routed to the brain. The bitter compounds thus activate both the taste receptors on the cell surface, as well as the signaling pathway proteins in the intracellular space. Intracellular signaling may be slower than taste cell receptor activation since more time is necessary for the bitter compounds to diffuse across the cell membrane and interact with intracellular proteins. This delayed activation of intracellular signaling proteins in response to the bitter compounds, in addition to the extracellular receptor signaling is proposed to be related to the lingering aftertaste associated with bitter foods. The combination of both mechanisms leads to an overall longer response of the taste receptor cells to the bitter foods, and aftertaste perception subsequently occurs.
Aftertaste processing in the cerebral cortex
The primary taste perception areas in the cerebral cortex are located in the insula and regions of the somatosensory cortexPostcentral gyrus
The lateral postcentral gyrus is a prominent structure in the parietal lobe of the human brain and an important landmark. It is the location of primary somatosensory cortex, the main sensory receptive area for the sense of touch...
; the nucleus of the solitary tract located in the brainstem also plays a major role in taste perception. These regions were identified when human subjects were exposed to a taste stimulus and their cerebral blood flow measured with magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
. Although these regions have been identified as the primary zones for taste processing in the brain, other cortical areas are also activated during eating, as other sensory inputs are being signaled to the cortex.
For aftertaste, much is unclear about the cortical processing related to its perception. The first neuroimaging study to evaluate the temporal taste profile of aspartame
Aspartame
Aspartame is an artificial, non-saccharide sweetener used as a sugar substitute in some foods and beverages. In the European Union, it is codified as E951. Aspartame is a methyl ester of the aspartic acid/phenylalanine dipeptide. It was first sold under the brand name NutraSweet; since 2009 it...
, an artificial sweetener, in humans was published in 2009. In it, the insula was observed to be activated for a longer period of time than other sensory processing areas in the brain when the aftertaste profile of aspartame was measured. Subjects were administered a solution of aspartame for a specific amount of time before being instructed to swallow the solution. Functional magnetic resonance images of the blood flow in the subjects’ brains were recorded before and after they swallowed the aspartame solution. Before swallowing, the amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
, somatosensory cortex, thalamus
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
, and basal ganglia
Basal ganglia
The basal ganglia are a group of nuclei of varied origin in the brains of vertebrates that act as a cohesive functional unit. They are situated at the base of the forebrain and are strongly connected with the cerebral cortex, thalamus and other brain areas...
were all activated. After swallowing, only the insula remained activated and the response of the other brain regions was not evident. This suggests that the insula may be a primary region for aftertaste sensation because it was activated even after the aspartame solution was no longer present in the mouth. This finding aligns with the insula’s identification as a central taste processing area and simply expands its function. An explanation for less activation of the amygdala was that because it is a reward center in the brain, less reward would be experienced by the subjects during prolonged exposure to the aspartame solution.
Distinguishing aftertaste and flavor
FlavorFlavor
Flavor or flavour is the sensory impression of a food or other substance, and is determined mainly by the chemical senses of taste and smell. The "trigeminal senses", which detect chemical irritants in the mouth and throat as well as temperature and texture, are also very important to the overall...
is an emergent property that is the combination of multiple sensory systems including olfaction
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...
, taste, and somatosensation
Somatosensory system
The somatosensory system is a diverse sensory system composed of the receptors and processing centres to produce the sensory modalities such as touch, temperature, proprioception , and nociception . The sensory receptors cover the skin and epithelia, skeletal muscles, bones and joints, internal...
. How the flavor of a food is perceived, whether it is unpleasant or satisfying, is stored as a memory so that the next time the same (or a similar) food is encountered, the previous experience can be recalled and a decision made to consume that food. This process of multisensory inputs to the brain during eating, followed by learning from eating experiences is the central idea of flavor processing.
Richard Stevenson mentions in The Psychology of Flavour that people often do not realize that a food’s flavor can be described by the food’s smell, taste, or texture. Instead, he claims, people perceive flavor as a “unitary percept”, in which a descriptor for either taste or smell is used to describe a food’s flavor. Consider the terms that are used to describe the flavors of foods. For instance, a food may taste sweet, but oftentimes its flavor is described as such while not considering its smell or other sensory characteristics. For example, honey tastes sweet so its smell is associated with that descriptor, and sweet is also used to describe its flavor. In fact, sweetness is one of the four basic taste qualities and only comprises part of a food’s flavor.
Unlike flavor, aftertaste is a solely gustatory event that is not considered to involve any of the other major senses. The distinction of being based on one (aftertaste) versus multiple (flavor) sensory inputs is what separates the two phenomena.
Artificial sweeteners
Low-calorie artificial sweeteners like saccharinSaccharin
Saccharin is an artificial sweetener. The basic substance, benzoic sulfilimine, has effectively no food energy and is much sweeter than sucrose, but has a bitter or metallic aftertaste, especially at high concentrations...
and acesulfame-K
Acesulfame potassium
Acesulfame potassium is a calorie-free artificial sweetener, also known as Acesulfame K or Ace K , and marketed under the trade names Sunett and Sweet One. In the European Union, it is known under the E number E950...
are known for their bitter aftertastes. Recently, GIV3727 (4-(2,2,3-trimethylcyclopentyl) butanoic acid), a chemical that blocks saccharin and acesulfame-K activation of multiple bitter taste receptor
Taste receptor
A Taste receptor is a type of receptor which facilitates the sensation of taste.Examples include TAS2R16 and TAS2R38.They are divided into two families:* Type 1, sweet, first characterized in 2001: –...
s has been developed. In the study, the addition of the bitter taste receptor antagonist
Receptor antagonist
A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses...
GIV3727 to the saccharin and acesulfame-K solutions resulted in significantly lower taste intensity ratings when compared to the solutions that were not treated with GIV3727. This suggests that GIV3727 inhibits the normal functions of the bitter taste receptors because saccharin and acesulfame-K's bitter aftertastes were not observed. The ability to inhibit activation of the bitter taste receptors can have far-reaching effects if the bitter aftertastes of not only these two artificial sweeteners but also other foods, beverages, and even pharmaceuticals can be minimized.
Wine
In wine tastingWine tasting
Wine tasting is the sensory examination and evaluation of wine. While the practice of wine tasting is as ancient as its production, a more formalized methodology has slowly become established from the 14th century onwards...
the aftertaste or finish of a wine, is an important part of the evaluation. After tasting a wine, a taster will determine the wine’s aftertaste, which is a major determinant of the wine’s quality. The aftertaste of a wine can be described as bitter, persistent, short, sweet, smooth, or even non-existent. Included in assessing the aftertaste of a wine is consideration of the aromas still present after swallowing. High quality wines typically have long finishes accompanied by pleasant aromas. By assessing the combination of olfactory and aftertaste sensations, wine tasting actually determines not only the aftertaste profile of a wine, but its flavor profile as well.