Rasa

The Sanskrit term “rasa” denotes a wide spectrum of meanings viz. “sap”, “juice”, “essence”, “taste, flavor”, “delight”, “charm,” and “sentiment,” etc. In Ayurveda, the term denotes taste/flavor, primary circulating nutritional fluid (ahararasa), fresh juice of plant (svarasa). In the context of rasashastra it indicates quicksilver, mercury (parada) and other precious metals. In Ayurveda, the primary taste is one of the identifying markers of the dravya. Apart from the contemporary meaning of taste, the concept of rasa has a wider pharmacological approach. The taste plays a vital role in deriving the pharmacological activity profile of the medicines. A physician, well acquainted with the classification of rasa and dosha, seldom commits blunders in ascertaining the etiology, symptomatology, and treatment of diseases. This chapter describes concept of rasa (taste) with its applications in pharmacotherapeutics.

Contributors

Section/Chapter/topic	Concepts/Prakriti/Manas prakriti
Authors	T.Saketh Ram1, Deole Y.S.2
Reviewer	Basisht G.3,
Editor	Basisht G.3
Affiliations	1National Institute of Indian Medical Heritage, C.C.R.A.S. Hyderabad, India 2Department of Kayachikitsa, G. J. Patel Institute of Ayurvedic Studies and Research, New Vallabh Vidyanagar, Gujarat, India 3Rheumatologist, Orlando, Florida, U.S.A.
Correspondence emails	dr.saketram@gmail.com, dryogeshdeole@gmail.com carakasamhita@gmail.com
Publisher	Charak Samhita Research, Training and Development Centre, I.T.R.A., Jamnagar, India
Date of publication:	November 18, 2022
DOI	In process

Usage of term “rasa” in different Indian Knowledge systems

The term rasa is used for denoting various meanings in various classical knowledge systems as below.

Table 1: Different meanings of rasa

Name of the Indian Knowledge System	Usage of the term “rasa”
Ayurveda	Taste, flavour as perceived by tongue; Primary circulation nutritional fluid (rasadhatu) Fresh Juice of a plant (svarasa)
Rasa shastra	Mercury; any precious metal as gold.
Nyaya, Vaisheshika Darshana	Taste as perceived by tongue;
Natya shastra (theatrics and dramaturgy), Kavya shastra (science of poetry), Shilpa shastra (iconography)	“sentiment” or “aesthetic sense” or “emotion”; rasa is the name given to bhava when it is immediately apprehended by the consciousness without veils. Shringara(the erotic), hasya(the comic), karuṇa (the pathetic), raudra (the furious), veera(the heroic), bhayanaka(the fearful), bibhatsa(the disgusting), adbhuta (the wondrous). shanta(the peaceful)
Ganita shastra (Mathematics and Algebra)	Term denotes number “six” and number “nine”; six is based on six tastes and nine is based on nine emotions; In general practice for six “ritu (seasons)” is employed instead of six tastes e.g. rituchakra denoting sixth group in 72 melakara ragas of Carnatic music.
Miscellaneous usage	Water, any liquid as milk, ghee, oil etc., nectar, semen, exudation- plant resin etc.,

Etymology & derivation

rasa: masculine vocative singular stem: rasa
As per “Dhatuvritti, 316” the root √rasaderives the meaning “āsvādanasnehanayoḥ (रसआस्वादनस्नेहनयोः।रसयति।रसतिइतिअपिशपि।)” which may be broadly understood in the following manner: The Sanskrit “rasa” is composed of two roots “ra” means “giving” “bestowing” “granting” “yielding” and “sa” means “wisdom” “knowledge” “paradise”. Together these roots create “rasa” meaning “to grant knowledge,” “to yield happiness,” “to bestow paradise,” all of which are the “essence” of life, so the Sanskrit dictionary defines “rasa” as “essence”.
This article deals with the aspect of rasa as taste/flavor.

Definition

Taste is the object of the gustatory sense organ and is in substance (dravya). Taste is perceived when a substance comes into contact with the tongue, gustatory sense organ (nipata). It is perceived through direct perception (pratyaksha) and based on inference (anumana) through consequent actions e.g. salivation.

Discussion regarding the number of rasa

The number of tastes, which has been the subject of much debate in Charak Samhita and ranges from one to infinite, is ultimately determined to be six. [Cha.Sa. Sutra Sthana 26/28]

Number of Rasas	Details	Proposed by	Explanation by Punarvasu Atreya
One	Water (apya)	Bhadrakapya	This theory supposes that water (jala) which is the abode (adhara) of the taste (rasa)-attribute (adheya) as one and the same, hence cannot be accepted.
Two	1. Sharp, weight reducing (Chhedaniya, langhana) 2. Pacifying, nourishing, weight increasing (upashamaniya, brimhaniya)	Shakunteya Brahmana	The argument is based on activity of the ingredient and not specific to taste, hence not acceptable.
Three	Above two and ordinary (Sadharana)	Purnaksha Moudgalya	Same as above
Four	1. Liked and wholesome (Svaduhita) 2. Liked but not wholesome (Svadu-ahita) 3. Disliked but wholesome (asvaduhita) 4. Disliked and unwholesome (asvadu-ahita)	HiranyakshaKoushika	Same as above
Five	1. Earth element predominant (Bhauma) 2. Water element predominant (Udaka) 3. Fire element predominant (Agneya) 4. Air element predominant (Vayavya) 5. Space element predominant (Akashiya)	Kumarashira Bharadwaja	The group represents substances in general and not specific to taste, hence not acceptable.
Six	1. Heavy (guru) 2. Light (laghu) 3. Cold (shita) 4. Hot (ushna) 5. Oily (Snigdha) 6. Non-oily, dry (ruksha)	Vayorvida	The argument is based on activity of the ingredient and not specific to taste, hence not acceptable.
Seven	1. Sweet (madhura) 2. Sour (amla) 3. Salt (lavana) 4. Katu (pungent) 5. Bitter (tikta) 6. Astringent (kashaya) 7. Alkaline (kshara)	Nimi	First six among this group are acceptable, however alkalinity (seventh entity) which is considered as part of saline taste cannot be a separate entity. Hence tastes are six only.
Eight	Above seven, unperceivable, tastelessness (avyakta)	BadishaDhamargava	In consideration to the above argument and alsoabsurdity of counting tastelessness as a separate taste, this proposition is not acceptable.
Innumerable	Due to various permutations and combinations tastes are innumerable.	Kankayana	Innumerability of tastes cannot serve the purpose of understanding a substance and its actions as taste as an attribute in a substance (abode) act in consonance with other entities like quality and action.

Vagbhata’s justification for six rasa count

"Some may argue that recognizing tastes as only six is untenable because variances in sweetness, oil, jaggery, and other items included within the sweet group (madhuraskandha). Let these disparities cease to exist or become the same by their non-recognition. These minute variations are ascribed to the bigger or smaller proportion of the elemental composition that coexists in the material that is not particularly differentiating and explained in detail. Because they all fall under a single category, the numerous distinctions in attributes, such as heaviness, etc., are also not listed individually. Similar circumstances apply to tastes. Ghee and others have the property of clinging to the mouth, whereas pomegranate fruit and others do not. Because of this, there are only six tastes, despite each of them having countless variations.”[A.S. Sutra Sthana 17/31-43]

Taste composition based on five primary elements

According to the Rasavaisheshika, one may deduce the main elemental makeup of tastes based on characteristics (guna). By grouping tastes according to degrees in terms of six major tastes, the Charak Samhita has provided a clear hint and denotes the proportionate existence of fundamental elements in them.

Using this as a criterion, the elemental makeup of tastes may be deduced. Additionally, the relative positions of the components in each taste should be set appropriately so one can understand both the contribution of the critical features and their relative predominance. For instance, sour and salty tastes are fiery (agneya). The salty taste is considered heavier than the sour taste (which has a water element) due to the prominence of the earth element, which is heavier than water element.

Similarly, because the bitter taste is lighter than pungent, the air element is the initial component in the former. Chakrapani's claim that heaviness or lightness cannot be determined based on elemental composition is untrue, since the theory of the five main elements (panchamahabhuta) forms the foundation of Ayurveda, is the only criterion that can be used to determine a substance's qualities.

As previously stated, the elemental makeup of tastes can be deduced from qualities and effects on dosha, tissues, excretory products, digestive fire, and bodily channels. For example, sweet taste promotes kapha dosha, nutriet fluid (rasa), semen (shukra). Therefore it is apparent by the law of similarity (samanya), and distinctness (vishesha) that sweet is likewise comprised of the earth element and water like kapha, etc. Astringent taste hardens watery fecal matter in diarrhea, indicating the presence of earth element. The appealing and pitta-aggravating characteristics of pungent, sour, and salty tastes demonstrate their igneous origin. The presence of space element is demonstrated by the effectiveness of bitter taste in disorders induced by congestion in channels.

Why are just two factors involved in the synthesis of tastes? This is because each taste affects two doshas by aggravating or alleviating them. Sweet taste, for example, soothes two doshas, vata and pitta, and so forth. As a result, the two components represent two doshas.

Table 3: Elemental composition for each taste

S.No.	Rasa	Charaka Samhita	Sushruta Samhita	AsthangaSangraha	Rasavaisheshika
1.	Madhura (sweet)	Aap, prithvi	Prithvi, Aap	Prithvi, Aap	Prithvi, Aap
2.	Amla (sour)	Prithvi, Agni	Aap, Agni	Prithvi, Agni	Aap, Agni
3.	Lavana (salty)	Aap, Agni	Prithvi, Agni	Aap, Agni	Agni, Aap
4.	Katu (pungent)	Vayu, Agni	Vayu, Agni	Vayu, Agni	Vayu, Agni
5.	Tikta (bitter)	Vayu, Akasha	Vayu, Akasha	Vayu, Akasha	Akasha, Vayu
6.	Kashaya (astringent)	Vayu, Prithvi	Prithvi, Vayu	Vayu, Prithvi	Prithvi, Vayu

It is proposed that the taste is directly perceivable when the substance comes in contact with tongue, whereas the elemental composition is understood by inference based on action.

Relationship between taste and three doshaunderstood through elemental composition

The six tastes have a logical relationship with the three dosha; three tastes pacify, and the other three aggravate each of them. The sweet, sour, and salty tastes pacifying vata, while the other three aggravate it. The pungent, bitter, and astringent tastes pacify kapha, while the other three aggravate it. The astringent, bitter, and sweet tastes pacify pitta, while the other three vitiate it. [Cha.Sa. Sutra Sthana 1/66] There seems to be a strong association between the number of tastes and the quantity of dosha.

Rasa	Prithvi	Aap/Jala	Teja	Vayu	Akasha	Vata	Pitta	Kapha
Madhura	+	++				Shamaka (pacifies)	Shamaka	Vardhaka (aggravates)
Amla		+	+			Shamaka	Vardhaka	Vardhaka
Lavana	+		+			Shamaka	Vardhaka	Vardhaka
Katu			+	+		Vardhaka	Vardhaka	Shamaka
Tikta				+	+	Vardhaka	Shamaka	Shamaka
Kashaya	+				+	Vardhaka	Shamaka	Shamaka

Relationship between six important qualities and taste

According to six major properties, the six tastes are arranged in order of degrees of predominance as follows:

Table 4: Relation of guna and rasa

Guna	Rasa
Heavy to digest (guru)	Sweet, astringent, salty tastes
Light to digest (laghu)	Bitter, pungent, sour
Unctuous (snigdha)	Sweet, sour, salty taste
Dry (ruksha)	Astringent, pungent, bitter
Cold (sheeta)	Sweet, astringent, bitter
Hot (Ushna)	Salty, sour, pungent

Table 5: Grading of tastes as per qualities.

Property	Maximum	Moderate	Minimum
Dry (ruksha)	Kashaya	Katu	Tikta
Oily (snigdha)	Madhura	Amla	Lavana
Hot (ushna)	Lavana	Amla	Katu
Cold (sheeta)	Kashaya	Madhura	Tikta
Guru (heavy to digest)	Madhura	Kashaya	Lavana
Laghu (light to digest)	Tikta	Katu	Amla

Among the twenty characteristics beginning with heaviness (gurvadiguna), the six listed above are the most prominent, achieving the level of potency (virya). They distinguish three levels of prominence: superior, medium, and inferior. The dravya (substances) with sweet taste predominantly have heavy to digest, unctuous, and cold qualities.

The dravya with bitter, astringent, and salty tastes predominantly have light to digest, dry, and hot properties.

Primary taste and adjunct, secondary taste (anurasa)

Every substance has a primary taste (pradhana rasa) and adjunct or secondary taste (anurasa). The unmanifested taste is referred to as adjunct taste (anurasa). For example, when chewing chebulic myrobalan (haritaki), an astringent taste is exhibited. While the other four tastes remain unmanifested. Therefore, adjunct taste (anurasa) becomes manifested at the end, such as the emergence of sweet taste, etc. As with Indian gooseberry (amalaki), the sour taste comes first, followed by other tastes.
According to Charak samhita, the first manifested taste of a material when it comes into touch with the tongue in a dry condition is recognized as the principal taste. It signifies that the main taste is the one that remains in the dry state and is experienced clearly. Whereas the adjunct taste is only present in the fresh form and is exhibited minimally towards the end. Chakrapanidatta interprets that taste and adjunct taste can be distinguished by manifestation; the former is manifested in all states, whereas the latter is always unmanifested and is known only by its faint appearance or inference from its action. However, that adjunct taste is felt in the end is a common experience, which is why Vagbhata has modified the definition accordingly.

Therefore, to simplify this, the first manifested taste is the principal rasa, and the one manifested at the end is the adjunct or secondary rasa of the substance.

The effect of tastes on the body

1. Sweet taste:
Sweet taste pacifies vata and pitta while increasing kapha dosha, increases vigor, and aids elimination. Excessive usage causes polyuria (prameha) and other problems. While its absence may create illnesses related to vata dosha and pitta dosha aggravation.
2. Sour taste:
Sour taste stimulates kapha dosha and pitta dosha, while pacifying vata. It reduces semen, and serves as a carminative, appetizer, and digestive. Excessive usage produces hyperacidity (amlapitta), and not taking it might cause a decrease in digestive capacity (agnimandya), among other things.
3. Salty taste:
Salty taste stimulates kapha dosha and pitta dosha, and pacifies vata dosha. It also decreases reproductive components (shukra dhatu) and is carminative, appetizer, digestive, and moistening. When taken in excess, it vitiates the blood and creates oedema. When not taken sufficiently, it causes loss of appetite, and vata-predominant illnesses. The characteristic of salt is moistening (vishyandi). It attracts and dissolves in water. As a result of fluid retention, heavy usage causes blood problems and oedema. That is why salt is not permitted in certain disorders.
4. Pungent taste:
Pungent tase promotes vata dosha and pitta dosha, while decreasing kapha dosha. It decreases reproductive components (shukra dhatu), regulates vata, stool, and urine flow, and activates digestive functions. When used excessively, it causes vata dosha and pitta dosha disorders. When not used at all, it causes kapha dosha disorders.
5. Bitter taste:
Bitter taste is absorbent and cleanses channels while soothing kapha dosha and pitta dosha. When used extensively, vata dosha disorders arise.
6. Astringent taste:
Astringent taste, pacifies kapha dosha and pitta dosha, while increasing vata dosha. It checks and suppresses digestive functions. Excessive usage produces vata prominent illnesses, and non-use causes kapha dosha and pitta dosha predominant ailments, as well as tissue loss.

Detailed description of actions of the tastes:

Name of the taste	Action
Sweet taste	Amongst the six rasas, the madhura rasa, because of its suitability to the body, promotes rasa dhatu, rakta, mamsa, meda dhatu, asthi dhatu, majja dhatu, ojas and shukra. It is also conducive to increasing the lifespan of the person, is pleasing to the six sense organs, promotes strength and lustre, alleviates pitta and vayu, neutralizes poisons, and pacifies thirst and heat. It is beneficial for skin, hair, throat and strength and is nourishing, vitalizing, saturating, bulk-promoting and stabilizing. It promotes healing of wounds of the emaciated. It provides good feeling in nose, mouth, throat, lips and tongue; alleviates fainting, is most liked by the bees and ants, and is unctuous, cold and heavy. Madhura rasa atiyoga (Effects of over consumption of sweet taste) [NAMC Code- Q-12.1] This rasa, though having so many qualities, if used singly and excessively, causes obesity, softness, laziness, excessive sleep, heaviness, loss of desire for food, poor digestion with mildness of appetite, abnormal growth in mouth and throat, dyspnea, cough, coryza, alasaka, fever with shivering, hardness of stool, sweetness in mouth, vomiting, loss of consciousness and voice, goitre, cervical adenitis, filariasis, pharyngitis, (mucous) coating in bladder, arteries and throat, eye diseases, conjunctivitis etc
Sour taste	Amla rasa makes food relishing, stimulates agni, enhances body bulk and energizes it, awakens the mind, firms the sense organs, increases bala (strength), causes vatanulomana (normal movement of vata), nourishes the heart, increases secretions in the mouth, propels, moistens, and digests food, gives satisfaction, and is light, hot and unctuous. Amla rasa atiyoga (Effects of over consumption of sour taste) [NAMC:Q-12.2] This, though endowed with so many qualities, if used singly and excessively, makes teeth sensitive, causes thirst, causes closure of eyes, raises the body hair, liquifies kapha, aggravates pitta, affects blood morbidity, causes inflammation in muscles and laxity in body, produces swelling in wasted, injured, emaciated and debilitated persons, because of its agneya nature causes suppuration in wounds, injuries, bites, burns, fractures, swellings, dislocations, poisoned spots due to urination and contact of insects, compressed, excised, incised, punctured and crushed etc., and causes burning sensation in throat, chest and the cardiac region
Salt	Lavana rasa is digestive, moistening, appetizing, pouring, expectorant, mass-breaking, irritant, laxative, quickly spreading in body, oozing, space-creating, vata alleviating, diminishes stiffness, viscid, diminishes the perception of other tastes if added in excess, increases secretions in mouth, liquefies kapha, cleanses channels, softens all the body-parts, gives relish to food, is a supplement of food. It is not very heavy, unctuous and hot. Lavana rasa atiyoga (Effects of over consumption of salty taste) [NAMC:Q-12.3] This, though having so many qualities, if used singly and excessively, vitiates pitta, aggravates rakta, causes thirst, fainting, heat, tearing, sloughing, increases leprosy and other skin diseases, aggravates poisons, weakens teeth, aggravates inflammations, impairs potency, hinders sense organs, gives rise to wrinkles, grey hair and baldness, and also produces disorders like internal hemorrhage, acid gastritis, erysipelas, vatarakta, eczema, alopecia etc.
Pungent taste	Katu rasa cleanses mouth, stimulates digestion, absorbs food, causes secretion from the nose and eyes, makes the sense organs clear, alleviates alasaka, swelling, corpulence, urticarial patches, blocked channels, unction, sweating, moisture and dirt, making food relishing, destroys itching, depresses wounds, kills germs, scrapes muscles, checks the coagulation of blood, cuts the bindings, expands the channels, pacifies kapha, and is light, hot and rough. Katu rasa atiyoga (Effects of over consumption of pungent taste)[NAMC:Q-12.4] This though having so many properties, if used singly and excessively, can damage sexual potency due to the effect of vipaka, cause mental confusion, malaise, depression, emaciation, fainting, bending, feeling of darkness, giddiness, burning in throat, body-heat, loss of strength and thirst due to the effect of rasa and veerya and prabhava, over and above, due to abundance of vayu and agni, it produces vatika disorders in feet, hands, sides, back etc. particularly with symptoms like dizziness, burning pain, tremors, piercing and tearing pains.
Bitter taste	Tikta rasa, though itself non-relishing, enhances appetite, is anti-poison, anthelmintic, alleviates fainting, burning sensation, itching, skin disorders and thirst, provides firmness to skin and muscles, is antipyretic, appetizer, digestive, galactodepurant (i.e., an agent that cleanses any adverse reaction of milk), lekhana (making thin), absorbs moisture, reduces fat, muscle-fat, marrow, lymph, pus, sweat, urine, feces, pitta and kapha; and is rough, cold and light. Tikta rasa atiyoga (Effects of over consumption of bitter taste) [NAMC:Q-12.5] This, though possessing so many qualities, if used singly and excessively, on account of its roughness, coarseness and non-sliminess, dries up rasa dhatu, rakta dhatu, mamsa dhatu, meda dhatu, asthi dhatu, majja dhatu and shukra dhatu, causes coarseness in channels, takes away strength, produces emaciation, malaise, mental confusion, giddiness, dryness of mouth and other vatika disorders
Astringent taste	Kashaya rasa is pacifying, astringent, union-promoting, compressing, healing, absorbing, checking (discharges), pacifies kapha, rakta and pitta, utilizes the body fluid, is rough, cold and slightly light. Kashaya rasa atiyoga (Effects of over consumption of astringent taste) [NAMC: Q-12.6] This, though possessing so many qualities, if used singly and excessively, dries up mouth, causes heart-ache, it causes distended abdomen, obstructs speech, constricts body channels, darkens complexion, decreases reproductive potency, delays digestion, causes distension of abdomen, checks flatus, urine, feces and semen, produces emaciation, malaise, thirst, stiffness, and because of its coarseness, non-sliminess and roughness, causes vatika disorders like hemiplegia, spasm, convulsions, facial paralysis etc.

Table depicting the degree of activity of taste on dosha

Dosha	First	Second	Third
Vata	Lavana	Amla	Madhura
Pitta	Tikta	Madhura	Kashaya
Kapha	Katu	Tikta	Kashaya

Combination of tastes

Although there are six main rasa, as was mentioned, their various mixtures form the basis of daily and therapeutic use. There are 63 possible combinations, which might include two, three, four, five, or six tastes. The following are the possible combinations.

Combination of two rasa	15
Combination of three rasa	20
Combination of four rasa	15
Combination of five rasa	6
Combination of all the six rasa	1
Singly (each rasa)	6
Total	63

Taste perception: Current understanding

As per current biomedical understanding, there are five primary taste sensations viz., salty sour sweet bitter umami ()

Overview of the mechanism of taste perception

Each taste bud comprises 50-100 taste cells that represent all five flavors. The apical surface of every taste cell is covered in receptors. These are transmembrane proteins that allow the chemicals that cause the flavors of sweet, bitter, and umami to bind to the ions that provide the taste of salt. It appears that a single taste cell can only express one type of receptor (except for bitter receptors). Action potentials in a neighboring sensory neuron that connects to the brain are set off by a stimulated taste receptor cell. However, in each of the several taste buds, a single sensory neuron can connect to a number of taste cells. The brain is where all sensations, including taste, originate.

Taste	Plausible mechanism of taste detection
Salty	The sodium ion channel that is activated by table salt (NaCl) in mice and possibly humans allows sodium ions (Na) to enter the cell directly, depolarizing it and causing action potentials in neighboring sensory neurons. The hormone aldosterone increases the number of these salt receptors in laboratory animals and maybe in humans. Biologically, this makes sense: Aldosterone's primary job is to keep the body's salt levels regular. An animal suffering from sodium deficiency (typically an issue for ungulates, including cattle and deer) would benefit from having a higher sensitivity to salt in its meal.
Sour	Protons (H) released by sour substances are detected by sour receptors (acids). This causes transmembrane K channels to close, which causes the cell to become depolarized and release the neurotransmitter serotonin into the space where it connects to a sensory neuron.
Sweet	G-protein-coupled receptors (GPCRs) are found on the cell surface and bind to sweet compounds (such sucrose, the table sugar). Each receptor consists of two T1R2 and T1R3 subunits that are connected to G proteins. Due of the G protein complex's structural and functional resemblance to the transducin, which is so crucial to rod vision, it has been given the name gustducin. A series of intracellular processes are triggered by gustducin activation, including the synthesis of the second messengers inositol trisphosphate (IP3) and diacylglycerol (DAG). This allows for the entry of Na ions, which depolarizes the cell and causes the release of ATP, which sets off action potentials in neighboring sensory neurons. It also releases intracellular Ca reserves. Leptin opens the K channels in sweet cells to suppress them. As a result, the cell becomes hyperpolarized, which makes it more challenging for action potentials to form.
Bitter	Bitter compounds like quinine and phenylthiocarbamide [PTC] bind to gustducin-coupled G-protein-coupled receptors as well, and the signaling pathway is the same as for sweet drugs (and umami). Each taste cell sensitive to bitter expresses several (4–11) of the 25 distinct bitter receptors ("T2Rs") that are encoded by human genes. Despite this, and for reasons that are still unknown, a single taste cell appears to respond to certain bitter-tasting molecules in preference to others. (This is in stark contrast to the system in olfaction where a single odor-detecting cell expresses only a single type of odour receptor.) The brain is where all sensations, including taste, originate. Transgenic mice express a receptor for a tasteless substance in cells that normally express T2Rs (bitter), which are repulsed by the tasteless material, and T2Rs in cells that normally express T1Rs (sweet), which respond to bitter things as though they were sweet. Therefore, neither the chemicals nor the receptors themselves, but rather the activation of hard-wired neurons, determines the perception of taste.
Umami	The reaction to glutamic acid salts, such as monosodium glutamate (MSG), a taste enhancer found in many processed foods and many Asian meals, is known as umami. Additionally, glutamate is present in processed cheeses and meats (proteins). On G-protein-coupled receptors that are connected to heterodimers of the protein components T1R1 and T1R3, amino acids, including glutamic acid, bind. The subsequent signalling chain is identical to that for sweet and bitter.

The generic purpose of taste perception

The majority of taste stimuli are non-volatile, saliva-soluble hydrophilic molecules. Examples include salts like NaCl, which are vital for maintaining electrolyte balance, essential amino acids like glutamate, which are required for protein synthesis, carbohydrates like glucose, which are required for energy, and acids like citric acid, which determine the taste of many foods (oranges, in the case of citrate). Plant alkaloids can be dangerous, including bitter-tasting compounds like atropine, quinine, and strychnine. Unless one "acquires a taste" for the chemical, as with quinine in tonic water, putting bitter substances in the mouth typically discourages intake.
The taste system encodes information about the quantity as well as the identity of stimuli. Generally speaking, the perceived intensity of flavour increases with increasing stimulus concentration. However, the majority of ingested tastants have fairly high threshold concentrations. For instance, the threshold value for sucrose is 20 mM, 10 mM for salt (NaCl), and roughly 2 mM for citric acid. Taste cells may only react to relatively high quantities of these necessary elements to promote an optimal intake since the body needs substantial concentrations of salt and carbs. The ability to identify potentially harmful substances (such bitter-tasting plant components) at far lower quantities is clearly helpful for the taste system. As a result, the threshold value for strychnine is 0.0001 mM and 0.008 mM for quinine. Gustatory sensitivity decreases with age, just as olfaction. Adults typically season food with more salt and spices than do kids. The decreased sensitivity to salt can be troublesome for older adults with issues with electrolyte and/or fluid balance. Unfortunately, there isn't presently a secure and reliable NaCl alternative.

Other Locations with Taste Receptors: There are numerous locations in the body where taste receptors can be discovered. Examples: The trachea and bronchi's cilia and smooth muscle cells include bitter receptors (T2Rs), which are likely used to expel inhaled irritants. The duodenum contains sweet receptors (T1Rs). In response to carbohydrates entering the duodenum, the cells release incretins. These lead to an increase in insulin secretion from the pancreas' beta cells. Therefore, rather than just detecting taste, "taste" receptors appear to also be able to sense substances in the surroundings.

Misconceptions about taste perception

Two frequent misunderstandings about taste perception exist. Which are as follows:

1. Rigid demarcation of certain areas on the tongue for each taste(15). The proposition that sweet is perceived at the tip of the tongue, salt along posterolateral edges, sour along mediolateral edges and bitter on theback of the tongue is initially proposed in 1901 by DeiterHanig. He has measured taste thresholds for NaCL, sucrose, quinine and hydrochloric acid (HCl). The proposition does not negate that rest of the areas are incapable of perceiving certain taste. It merely indicates that certain areas are more sensitive to perceive certain taste. However, certain areas having more sensitivity helps to adjust the behaviour of a person for intake of certain food item etc., e.g.
   1. Sweet taste: Since sweet substances provide pleasurable sensations, the tip of the tongue is especially sensitive to them, and input from this area stimulates feeding behaviours such mouth movements, salivary production, insulin release, and swallowing.
   2. The back of the tongue does indeed respond to bitter chemicals the best. Bitter chemicals that activate this region cause the tongue to protrude and other defensive reflexes that stop swallowing.
   3. Sour substances cause grimaces, puckering reactions, and a lot of salivation to be secreted to mask the tastant.
2. The idea that there are only four "basic" tastes—salt, sweet, sour, and bitter—is another fallacy about taste perception.If this were the case, then any combination of these "primaries" could represent any taste. These four tastes do represent unique sensations, yet it is evident that this categorization is constrained. Additional tastes that people feel include astringency (from cranberries and tea), pungency (from hot pepper and ginger), fattiness, starchiness, and various metallic tastes (to name but a few). But none of this fall under any of these four groups. Additionally, in some cultures, certain tastes are regarded as "primary." For instance, the Japanese believe that the tastes of monosodium glutamate differs from that of salt and even give it a new name ("umami," which translates to "delicious"). Last but not least, combining different compounds can produce completely different tastes. It is possible to estimate the number of scents that are perceived (about 10,000), but due to these uncertainties, it is challenging to determine the number of tastes. There is no obvious connection between "basic" perceptual classes and the cellular and molecular machinery of sensory transduction in either taste or olfaction.

Applications of taste perception

Ayurveda relies on the concept of taste perception in matters of nutrition to a great extent. Apart from this, it is also utilized for understanding the properties of therapeutic materials, their judicious usage and diagnosis of certain disorders etc. Some of such important uses are explained here:

Nutrition: Importance of using all the six tastes judiciously

Balanced use of all six tastes is recommended for dosha and tissue balance, and as such, just as excessive usage (atiyoga) can lead to abnormalities, so can non-use (ayoga). For example, suppose a sweet taste is not consumed. In that case, it may create vata dosha and pitta dosha aggravation owing to a decrease in kapha, which regulates them and avoids further diseases.

Taste perception as a tool for the diagnosis of disorders

An illustrative list of conditionsthat can be identified based on the taste are as follows :

Taste	English translation	Disease	Reference
Kashaya anurasastanya	astringent taste in breast milk	Vata dominant dushti	A.S.Su.36:16, Cha.Sha.8:55; S.N.JO:23; AS.U.2:4; Ah.N.2:3; M.N.67:2
Amlastanya	Sour taste in breast milk	Pitta dominant dushti	Cha.Sha.8:55; S.N.10:24; AS. U.2:5; Ah.N.2:3; M.N.67:2
Atṛuptikarastanya	Unsatisfactory feeding to infant	Vata dominant dushti	Cha.Sha.8:55
Kaṭukastanya	Pungent taste in breast milk	Pitta dominant dushti	Cha.Sha.8:55; S.N.10:24; Ah.N.2:3; M.N.67:2
Lavanastanya	Salty taste in breast milk	Pitta dominant dushti	M.N.67:2
Lavanastanya	Salty taste in breast milk	Kapha dominant dushti	Cha.Sha.8:55; AS.U.2:6; Ah.N.2:4
Madhura stanya	sweet taste in breast milk	Kapha dominant dushti	Cha.Sha.8:55
Tikta stanya	Bitter in breast milk	Pitta dominant dushti	Cha.Sha.8:55
Virasa stanya	Distaste in breast milk	Vata dominant duṣhṭi	Cha.Chi.30:237
Amla mutra	Urine with sour smell and taste	Amlameha	S.N.6:1l
Amla mutra	Urine with sour smell and taste	Nilameha	Cha.N.4:3; AS.N.10:8
Kashaya- madhura-mutra	Astringent and sweet taste in urine	Madhumeha	Cha.N.4:44; AS.N.10:8; M.N.33:16
Kaṭukaṃmutra	Pungent taste	Avikritamutra	S.Sa.12:20
Kaṭukaṃmutra	spicy taste	Haridrameha	Cha.N.4:34; AS.N.10:8; Ah.N.1O:15; M.N.33:14
Lavaṇatulyaṃmutra	salty urine	Lavanameha	S.N.6:1O
Lavaṇatulyaṃmutra	salty urine	Raktameha	Cha.N.4:32; AS.N.10:8; Ah.N.10:16; M.N.33:15
Madhuramutra	sweet taste	prameha purvarupa	S.N.6:5; AS.N.10:7
		Hastimeha	AS.N.10:8
		Ikshuvalikameha	Cha.N.4:11; AS.N.10:8; Ah.N.10:9; M.N.33:8
		Madhumeha	Ah.N.10:40
		Sitameha	Cha.Ni.4:19; AS.N.10:8; M.N.33:11
Amlodgara	Sour taste and smell in belching	Pittakopa	S.Su.21:27
		Raktakopa	Ah.Su.27:4
		Lavaṇa rasa atyupayoga	S.Su.42:10:3
		Snehan atiyoga	AS. Su.25:46
		Anuvasana atiyoga	AS. Su.28. 47
		Pitta kasa	Ah.N.3:25
		Paittika hṛidroga	Cha.Su.17:33; AS.N.5:44; Ah.N.5:41
		Paittikajirna	AS.Su.11:33; Ah.Su.8:26
		Panajirna	S.U.47:20
		Amlapitta	M.N 51 :2
		Kaphapaittika amlapitta	M.N 51 :11
		Urdhvagaamlapitta	M.N 51 :5
		Grahaṇi purvarupa	AS. N.8:21; Ah.N.8:19
		Grahaṇi	Cha.Chi.15:S4; S.U.40:175
		Pittagrahaṇi	Cha.Chi.IS:66# As. N.8:27# Ah.N.8:26# M.N.4:12
		Paittikagulma	Cha.Ni.3:9; AS. N.11 :38; Ah.N.11:44
		Pittajvara	AS. N.2:4; Ah.N.2:19
		Sheetajwara	AS. N.2:36; Ah.N.2:37
		Pittapaṇdu	Cha.Chi.16:22; AS. N.13: 12; Ah.N.13: 11
		Raktapitta purvarupa	Cha.N.2:6; AS. N.3:6; Ah.N.3:4
		Arsha purvarupa	S.N.2:8; AS. N.7:7; Ah.N.7: 18
		Sahaja arsha	Cha.Chi.14:8
		Pitta prameha	S.N.6: 13; AS. N.10:10; Ah.N.10:23; M.N.33:19
		paittika upavishṭaka	AS. Sa.4: 17
kaṭu-udgara	spicy taste and smell in belching	Rakta prakopa	Ah.Su.27:4
		Kaphaja amlapitta	M.N.51:11
Madhuraasyata	Sweet taste	Kaphaja grahaṇi	Cha.Chi.15:69; AS. N.8:30; Ah.N.8:28; M.N. 4: IS
Tiktaudgara	Belching with the bitter taste	Raktadushti	Cha.Su.24:14
		Paittika hridroga	Cha.Su.17:33
		Amlapitta	M.N. 51:2
		Kaphapittaja amlapitta	M.N. 51:11
		Urdhvaga amlapitta	M.N. 51:5
		Grahaṇi	C.Ci.15:54; S.U.40: 175
		Sahaja arsha	C.Ci.14:8

Rasa as a guiding tool for preventive and promotive health

Seasons and Rasa

The tastes of naturally growing substances differ according to climatic conditions and and seasons. The table represents names and basic characteristics of the common seasonal divisions in India. The sun moves to the north or south, but it always rises in the east and sets in the west. The movement to the north removes a lot of water from the overall environment, but the movement to the south allows water to enter or stay in the plants' surroundings. This is what determines whether plants in an ecosystem have access to fewer or more main elemental (mahabhuta) components. The plant kingdom's domination of one taste is due to their diverse contributions. This discovery regarding the taste of the majority of plants and the related characteristics of five element dominance has led to an understanding of the percentages of elements contributing.

Name of season	Ayana Solar move to direction	Mahaabhautika dominance as observed	Rasotpatti Dominant taste	Veerya of the Rasa	Dosha Dominance
Shishira (Cold)	Uttara (north)	Vayu + Akasha	Tikta (bitter)	Shita	Kapha
Vasanta (warm)	Uttara (north)	Vayu + Prithvi	Kashaya (astringent)	Shita	Kapha
Grishma (hot)	Uttara (north)	Vayu + Teja	Katu (pungent)	Ushna	Vata
Varshaa (rains)	Dakshina (south)	Jala + Agni	Amla (sour)	Ushna	Vata
Sharada (moist hot)	Dakshina (south)	Prithvi + Teja	Lavana (salty)	Ushna	Pitta
Hemant (cool)	Dakshina (south)	Prithvi + Jala	Madhura (sweet / bland)	Shita	Kapha

RituHaritaki- changes in administration of medicines as per season

Here is an illustration of how judicious combinationof different substances with varied tastes along with haritakiserve the purpose of mitigating illeffect in six seasons. This is one among the many applications of rasa theory in ayurvedic practice. The details are as follows:
The drug is significantly prescribed intherapeutic as well as preventive use and process of restorative or alternative indication (rasayanakarma), and it is classically recommended as rituharitakifor using the drug during the course of different seasons viz.,

• Varsha (rains) – saindhavalavana (rock salt)
• Sharada ritu(autumn) - sharkara (sugar)
• Hemanta (cold/winter) - Shunthi (dry ginger)
• Shishira (latewinter early spring)- pippali(long pepper)
• Vasanta (spring) - madhu (honey)
• Grishma (summer)- guda (jaggery)

Theses done

1. Kalpesh Panara. A Phytopharmacological Study on Certain Amla Rasa Predominant Plants w.s.r. to their Atiyoga. Post Graduate dissertation. Department of Dravyaguna Vigyan. I.P.G.T.& R.A., Jamnagar. 2012.
2. Krutika Joshi. A phytopharmacological study of certain Katu Rasa predominant plants wsr to their Atiyoga. Post Graduate dissertation. Department of Dravyaguna Vigyan. I.P.G.T.& R.A., Jamnagar. 2012.
3. Rasika Kolhe. A Phyto-pharmacological Study on Certain Kashaya Rasa Predominant Plants w.s.r. their Atiyoga. Post Graduate dissertation. Department of Dravyaguna Vigyan. I.P.G.T.& R.A., Jamnagar. 2012.
4. Shital Mehta. A Phyto-pharmacological Evaluation on Certain Tikta Rasa Predominant Plant w.s.r. to Atiyoga. Post Graduate dissertation. Department of Dravyaguna Vigyan. I.P.G.T.& R.A., Jamnagar. 2012.

Future scope of research

The exact mechanism of action of rasa to cause disorders needs to be researched and elaborated further. Taste sensitivity can be a valuable tool for the diagnosis of various systemic disorders. The biomarkers for diagnosis of diseases, and identification markers for plants based on taste perception can be investigated.

Acknowledgment: The technical contribution of Dr Shruti G, SRF (Ay.), and Dr Satyavrat Nanda, R.A (Sanskrit), NIIMH, Hyderabad is duly acknowledged.