Taste, a fundamental sense, allows organisms to chemically analyze potential foods and liquids. This chemical sensing ability is important for survival, enabling the identification of nourishing substances and the detection of harmful toxins.
How We Perceive Taste
Taste perception begins in the mouth with specialized sensory organs called taste buds. These taste buds are primarily located on the tongue’s surface, within small bumps called papillae, but also appear on the soft palate, epiglottis, and throat. Each taste bud contains 50 to 100 taste receptor cells, also known as gustatory cells.
When food or liquid enters the mouth, chemical compounds, called tastants, dissolve in saliva and interact with these taste receptor cells through tiny openings called taste pores. This interaction triggers a signaling cascade within the taste receptor cells, leading to an electrical signal. These signals are then transmitted via cranial nerves to the brainstem, then to the thalamus, and finally to the gustatory cortex in the brain, where they are interpreted as taste.
The Five Basic Tastes
The human gustatory system recognizes five distinct basic tastes, each signaling different chemical properties important for dietary assessment. These tastes are sweetness, sourness, saltiness, bitterness, and umami.
Sweet
Sweetness typically signals the presence of sugars, which are energy-rich compounds. Sugars like glucose and fructose, along with other substances such as some amino acids and alcohols, activate specific G protein-coupled receptors on taste receptor cells. This activation leads to the perception of sweetness.
Sour
Sourness indicates acidity and is often associated with unripe fruits, fermented foods, or spoiled items. This taste is primarily detected by the presence of hydrogen ions (H+), which are abundant in acidic solutions. Hydrogen ions can directly enter specific taste receptor cells, leading to an electrical signal that the brain interprets as sour.
Salty
Saltiness alerts the body to essential minerals and electrolytes, particularly sodium chloride. The sensation of saltiness is largely due to sodium ions (Na+) entering taste receptor cells through ion channels. This influx of sodium ions causes an electrical change in the cell, signaling the presence of salt to the brain.
Bitter
Bitterness often signals the presence of potential toxins or harmful alkaloids, acting as a protective mechanism. There are approximately 25 different bitter receptors in humans, each capable of detecting a wide range of chemically diverse bitter compounds, such as those found in coffee or dark chocolate. The activation of these G protein-coupled receptors initiates a signal.
Umami
Umami, often described as a savory or “delicious” taste, indicates the presence of proteins. This taste was scientifically identified in 1908 by Japanese scientist Kikunae Ikeda, who found that glutamate, an amino acid, was responsible for the savory taste in kombu seaweed broth. Umami is primarily detected by receptors that respond to glutamates and nucleotides, which are common in foods like mushrooms, aged cheeses, and ripe tomatoes.
Beyond Basic Tastes
While the five basic tastes are fundamental sensations detected by the tongue, the full experience of eating involves more than just taste. “Flavor” is a comprehensive sensory experience that combines taste with other sensory inputs. This includes the role of smell, where volatile compounds from food reach olfactory receptors in the nasal cavity, contributing to the overall perception.
Other sensations also contribute to flavor, such as texture (mouthfeel), which includes qualities like crispiness or creaminess, and temperature. Additionally, chemical sensations like the heat from capsaicin in chili peppers or the cooling effect of menthol are perceived through nerve endings in the mouth, not through taste buds, and are distinct from the basic tastes. These various inputs integrate in the brain to create the complex experience of flavor.