Molecular insights into human taste perception and umami tastants: A review

Abstract

Understanding taste is key for optimizing the palatability of seaweeds and other non‐animal‐based foods rich in protein. The lingual papillae in the mouth hold taste buds with taste receptors for the five gustatory taste qualities. Each taste bud contains three distinct cell types, of which Type II cells carry various G protein‐coupled receptors that can detect sweet, bitter, or umami tastants, while type III cells detect sour, and likely salty stimuli. Upon ligand binding, receptor‐linked intracellular heterotrimeric G proteins initiate a cascade of downstream events which activate the afferent nerve fibers for taste perception in the brain. The taste of amino acids depends on the hydrophobicity, size, charge, isoelectric point, chirality of the alpha carbon, and the functional groups on their side chains. The principal umami ingredient monosodium l‐glutamate, broadly known as MSG, loses umami taste upon acetylation, esterification, or methylation, but is able to form flat configurations that bind well to the umami taste receptor. Ribonucleotides such as guanosine monophosphate and inosine monophosphate strongly enhance umami taste when l‐glutamate is present. Ribonucleotides bind to the outer section of the venus flytrap domain of the receptor dimer and stabilize the closed conformation. Concentrations of glutamate, aspartate, arginate, and other compounds in food products may enhance saltiness and overall flavor. Umami ingredients may help to reduce the consumption of salts and fats in the general population and increase food consumption in the elderly.

Sodium Homeostasis, a Balance Necessary for Life

“…Na is detected by the taste system within the oral cavity. The mineral generates a salty taste that guides and maintains its consumption [ 11 , 12 , 13 , 14 ]. The gustatory stimulus used as prototype to study the perception of this taste was table salt (NaCl), physiologically the most important salt in the diet, which induces the purest salty taste [ 11 , 15 ], and biologically the most relevant to maintain biochemical balance [ 16 ].…”

“…There are four types of papillae according to their shape and localization: fungiform (anterior two-thirds of the tongue), foliate (side toward the back), circumvallate (on the back), and filiform (anterior two-thirds of the tongue). Cells that detect NaCl are mainly located in fungiform papillae [ 12 , 17 ]. In general, gustatory papillae can contain several hundreds of taste buds, onion-shaped organs ( Figure 2 ) that house taste receptor cells (50–100 cells each), i.e., the cells responsible for detecting and transducing taste stimuli (transforming chemical signals into neural activity).…”

“…In the taste bud, these cells are mechanically held together by tight junctions that separate apical areas from the remaining basolateral region, forming an almost impermeable barrier. Only the apical membrane above the tight junctions (2–3% of the total membrane area of the cell) is exposed to saliva, while the basolateral area remains in a relatively constant interstitial milieu [ 12 , 13 , 14 , 18 ].…”

“…The other type is activated by high (aversive) concentrations of NaCl (>150 mM), is amiloride-insensitive, and is non-selective for Na (other salts are equally effective). The latter type of taste receptor cells appears to be innervated by neural pathways associated more with aversion than with taste coding [ 12 , 14 , 19 , 20 ].…”

“…Taste reception begins when chemicals interact with taste receptors located at the apical segment of the taste cells. The receptors that mediate the transduction of salty taste are ion channels [ 12 , 19 ], designated epithelial Na channels (ENaCs), which are specialized in the detection or recognition of sodium chloride [ 11 , 12 , 15 , 16 , 19 ]. Interestingly, and as expected, it has been demonstrated that the gustatory response to Na in deficient animals can be augmented by some of the hormones involved in its regulation, e.g., aldosterone or angiotensin II (Ang II), through an increase in the number of active amiloride-sensitive Na channels in the apical membrane of taste cells [ 9 , 21 , 22 ].…”