Which four tastes are perceived by taste receptors?

Based on physiological and traditional sensory definitions, the four tastes classically perceived by the specialized receptors in the mouth are Sweet, Sour, Bitter, and Salty.

Key Takeaways

• The Four Primary Tastes: From a strict physiological standpoint, the traditional four tastes perceived by taste receptors are sweet, sour, bitter, and salty.
• The Fifth Taste (Umami): Many scientists and recent studies recognize a fifth basic taste, umami (savory/delicious flavor), which is also detected by taste receptor cells.
• Non-Taste Sensations: Sensations like pungency (spicy) and astringency are not true tastes perceived by taste receptors but rather by other sensory nerves (pain and tactile responses).

The Four Traditional Tastes Recognized by Receptors

Historically and physiologically, taste is defined by the rudimentary sensations that stimulate specific receptor mechanisms on the tongue and oral cavity. The four tastes that form the cornerstones of taste perception are sweet, sour, bitter, and salty.

This understanding originates from theories, such as the one proposed by German psychologist Henning in 1916, which established the four basic tastes (sweet, sour, salty, and bitter) that were long accepted as the complete set of primary tastes. These tastes are traditionally associated with specific areas of the tongue, though modern understanding shows broader distribution.

1. Sweet: Elicited by compounds like sugars, some amino acids (D-form, or L-series with small side chains), and artificial sweeteners.
2. Salty: Contributed by neutral salts, most commonly sodium chloride (NaCl), which is the only substance known to evoke a purely salty taste at suprathreshold concentrations.
3. Sour: Produced by hydrogen ions from organic acids, inorganic acids, and acidic salts.
4. Bitter: Typically elicited by alkaloids (like quinine or caffeine), certain electrolytes, and L-amino acids with large or long side chains (such as leucine, phenylalanine, or tryptophan).

Distinguishing True Tastes from Other Sensations

It is crucial to understand that many sensations we attribute to “taste” are actually perceived by other sensory inputs, not the basic taste receptors. From a physiological viewpoint, only the four classic tastes (sweet, sour, bitter, and salty) are perceived by taste receptors.

• Pungency (Spicy): This sensation is not a taste; it is the pain feeling caused when pungent substances stimulate the oral mucosa, nasal mucosa, and trigeminal nerve.
• Astringency: This is the response of tactile nerves to protein aggregation in the mouth, not a true taste.
• Metallic Taste: This factor is often included in sensory evaluation lexicons, particularly for meat products, and is sometimes attributed to the iron content from myoglobin and hemoglobin released during cooking. A metallic taste can also be stimulated by a mixture of sour and salt tastes.

The Context of Umami: The Fifth Taste

While the four tastes listed above form the historical and physiological core, recent research widely supports the existence of a fifth basic taste: umami. This distinction is important for consumers, especially concerning flavor enhancers:

• The Umami Receptor: Taste bud receptor cells (TRCs) are responsible for the detection of five basic tastes: sweet, sour, salty, bitter, and umami. Umami is described as a “savory,” “meaty,” or “delicious flavor”.
• Scientific Recognition: The umami taste is chemically represented by glutamates (like monosodium glutamate or MSG) and 5′-nucleotides (like 5′-inosine monophosphate or 5′-IMP). Psychometric, biochemical, and neuroelectrophysiological studies indicate that umami is located outside the traditional tetrahedron of the four basic tastes, establishing it as distinctly different.
• The Debate: Even with scientific support, the categorization is sometimes debated; some sources note that not all scientists are convinced that umami is a unique taste, suggesting the sensation it causes is simply a taste enhancer. However, the presence of umami compounds enhances the sensation of other tastes, often making foods taste fuller and more delicious.

The current understanding, therefore, acknowledges the four traditional tastes as the foundational components of taste chemistry, while simultaneously recognizing umami as an independent basic taste, bringing the total number of tastes detected by specific receptors to five.