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Taste: the story on HearLore | HearLore
Taste
Imagine a landscape of microscopic mountains and valleys covering your tongue, a terrain so complex that it holds the key to your survival and your pleasure. This is the reality of the human gustatory system, a sensory network that has been misunderstood for centuries. For most of human history, scientists believed there were only four basic tastes: sweet, sour, salty, and bitter. It was not until 1907 that a Japanese chemist named Kikunae Ikeda isolated a fifth taste, which he called umami, or savory, from the broth of seaweed. This discovery shattered the Western scientific consensus and revealed that the tongue is far more sophisticated than previously thought. The tongue is covered with thousands of small bumps called papillae, which are visible to the naked eye. Within each papilla are hundreds of taste buds, and each taste bud contains 50 to 100 taste receptor cells. These cells are not merely passive sensors; they are active participants in a chemical dance that determines whether you will eat a meal or spit it out. The exceptions to this rule are the filiform papillae, which do not contain taste buds, serving instead to provide texture and friction. The distribution of these buds is not limited to the tongue; they are also found on the roof of the mouth, the sides, the back of the throat, and even the epiglottis, ensuring that the body is constantly monitoring everything that enters the digestive tract.
The Chemistry Of Survival
The five basic tastes are not arbitrary categories but evolutionary survival mechanisms that have guided human behavior for millennia. Sweetness signals the presence of carbohydrates, which are essential for energy, while bitterness warns of potential poisons found in plant leaves and toxic substances. Sourness indicates acidity, which can signal under-ripe fruit or spoiled meat, while saltiness is critical for maintaining ion and water homeostasis in the body. The detection of salt is particularly important for mammals, as it serves as an osmotically active compound that facilitates the passive re-uptake of water into the blood. This is why salt elicits a pleasant taste in most humans, whereas high concentrations of salt can become unpleasant. The mechanism for detecting these tastes involves specific molecules binding to G protein-coupled receptors on the cell membranes of taste buds. Sweetness, savoriness, and bitter tastes are triggered by the binding of molecules to these receptors, while saltiness and sourness are perceived when alkali metals or hydrogen ions meet the taste buds. The brain interprets these signals to make immediate decisions about whether to consume or reject a substance. This system is so sensitive that the threshold for stimulation of bitter taste by quinine averages a concentration of 8 micromolar, and the most bitter substance known, denatonium, has an index of 1,000. This extreme sensitivity is a protective function, allowing humans to detect toxic compounds at very low thresholds.
When was the fifth taste umami discovered and by whom?
The fifth taste umami was discovered in 1907 by the Japanese chemist Kikunae Ikeda. He isolated the savory taste from the broth of seaweed and named it umami. This discovery shattered the Western scientific consensus that there were only four basic tastes.
What are the five basic tastes and their evolutionary purposes?
The five basic tastes are sweet, sour, salty, bitter, and umami. Sweetness signals carbohydrates for energy, sourness indicates acidity, saltiness maintains ion homeostasis, bitterness warns of poisons, and umami detects amino acids for building muscles and organs.
Who are supertasters and how does their genetics affect their taste experience?
Supertasters are individuals with an increased number of fungiform papillae on their tongues that experience heightened taste sensitivity. Their genetic variation at the TAS2R38 locus determines their ability to taste bitter substances like phenylthiocarbamide and 6-n-propylthiouracil. This genetic basis makes them require less fat and sugar while consuming more salt than others.
What is the difference between taste and chemesthetic responses on the tongue?
Taste involves specific molecules binding to receptors on taste buds to detect sweet, sour, salty, bitter, and umami flavors. Chemesthetic responses like heat and cold involve the trigeminal nerve and substances such as capsaicin or menthol. These sensations are not tastes but complex interactions between the nervous system and chemical properties of food.
Which animals have lost the ability to taste certain basic tastes and why?
Cats cannot taste sweetness while several carnivores like hyenas, dolphins, and sea lions have lost the ability to sense up to four of their ancestral five basic tastes. This loss of function resulted from changes in diet and environment that allowed these species to adapt to their specific ecological niches.
Not all humans experience the world of taste in the same way, and for a small but significant portion of the population, the sensory experience is amplified to an extreme degree. These individuals are known as supertasters, and their heightened sensitivity is likely due to an increased number of fungiform papillae on their tongues. Studies have shown that supertasters require less fat and sugar in their food to get the same satisfying effects, yet they tend to consume more salt than others. This is because their heightened sense of the taste of bitterness is so intense that the presence of salt drowns out the bitter taste, making their food choices distinct from the general population. The genetic basis for this variation is found in the TAS2R38 locus, which determines the ability to taste certain bitter substances like phenylthiocarbamide and 6-n-propylthiouracil. Among the tasters, some are so-called supertasters to whom these substances are extremely bitter, while others find them virtually tasteless. This genetic variation has been a source of great interest to those who study genetics and evolution, as it suggests that the ability to taste bitterness has been a critical factor in human survival. The variation in sensitivity is determined by two common alleles at the TAS2R38 locus, and this genetic diversity has allowed humans to adapt to different environments and dietary needs.
The Forgotten Tastes Of History
The history of taste research is a story of evolving understanding, from the ancient speculations of Aristotle to the modern molecular biology of the 21st century. In the West, Aristotle postulated in 350 BC that the two most basic tastes were sweet and bitter, and he was one of the first persons to develop a list of basic tastes. However, the concept of a savory taste was not present in Western science until the early 20th century, when Kikunae Ikeda isolated the chemical monosodium glutamate from dashi. The discovery of umami was a pivotal moment in the history of taste, as it revealed that the tongue could detect the presence of amino acids, which are critical for building muscles and organs. The history of taste also includes the use of lead acetate as a sweetener in ancient Rome, where Romans used to deliberately boil the must inside of lead vessels to make a sweeter wine. This practice led to lead poisoning, which was eventually discovered and banned. The history of taste is also a story of cultural evolution, as different cuisines have developed unique ways of enhancing flavor. For example, the Japanese concept of kokumi, or heartiness, describes compounds in food that do not have their own taste but enhance the characteristics when combined. This concept has been used to define the characteristic flavors of garlic and other ingredients, and it has been integrated into the modern understanding of taste.
The Science Of Spicy And Cool
The sensation of heat and cold on the tongue is not a taste in the technical sense, but rather a chemesthetic response that involves the trigeminal nerve. Substances such as ethanol and capsaicin cause a burning sensation by inducing a trigeminal nerve reaction together with normal taste reception. The sensation of heat is caused by the food's activating nerves that express TRPV1 and TRPA1 receptors. Some such plant-derived compounds that provide this sensation are capsaicin from chili peppers, piperine from black pepper, gingerol from ginger root, and allyl isothiocyanate from horseradish. The piquant sensation provided by such foods and spices plays an important role in a diverse range of cuisines across the world, especially in equatorial and sub-tropical climates. The sensation of coolness is also a chemesthetic response, triggered by substances such as menthol, anethol, ethanol, and camphor. This fresh or minty sensation is caused by the activation of the same mechanism that signals cold, TRPM8 ion channels on nerve cells. The sensation of numbness, known as má or mati rasa, is another chemesthetic response that is common in Chinese and Batak Toba cooking. This tingling numbness is caused by spices such as Sichuan pepper, and it is often combined with chili pepper to produce a málà, or numbing-and-hot, flavor. These sensations, although not taste, fall into a category of chemesthesis, which is a complex interaction between the nervous system and the chemical properties of food.
The Evolutionary Puzzle Of Taste
The evolution of taste has been shaped by the need to distinguish between safe and harmful food, and the ability to detect different tastes has varied across species. Not all mammals share the same tastes; some rodents can taste starch, which humans cannot, while cats cannot taste sweetness. Several other carnivores, including hyenas, dolphins, and sea lions, have lost the ability to sense up to four of their ancestral five basic tastes. This loss of function has been a result of changes in diet and environment, and it has allowed these species to adapt to their specific ecological niches. The ability to taste bitter-tasting, toxic compounds at low thresholds is considered to provide an important protective function, and plant leaves often contain toxic compounds. Among leaf-eating primates, there is a tendency to prefer immature leaves, which tend to be higher in protein and lower in fiber and poisons than mature leaves. The use of fire, changes in diet, and avoidance of toxins has led to neutral evolution in human bitter sensitivity, which has allowed several loss of function mutations that has led to a reduced sensory capacity towards bitterness in humans when compared to other species. This evolutionary history has shaped the way humans interact with food, and it has influenced the development of culinary traditions around the world.
The Future Of Flavor Science
The study of taste continues to evolve, with new discoveries revealing the complexity of the gustatory system and the potential for new flavors. Recent research reveals a potential taste receptor called the CD36 receptor, which binds to fat molecules and has been localized to taste bud cells. There is a debate over whether we can truly taste fats, and supporters of human ability to taste free fatty acids have based the argument on a few main points, including the evolutionary advantage to oral fat detection and the physiological response to the presence of oral fat. The main form of fat that is commonly ingested is triglycerides, which are composed of three fatty acids bound together. In this state, triglycerides are able to give fatty foods unique textures that are often described as creaminess, but this texture is not an actual taste. It is only during ingestion that the fatty acids that make up triglycerides are hydrolysed into fatty acids via lipases. The taste is commonly related to other, more negative, tastes such as bitter and sour due to how unpleasant the taste is for humans. The study of taste has also revealed the existence of other possible fat taste receptors, such as free fatty acid receptor 4 and free fatty acid receptor 1, which have been linked to fat taste. The future of flavor science promises to reveal even more about the complexity of the gustatory system and the potential for new flavors.