There is a debate over whether we can truly taste fats, and supporters of our ability to taste free fatty acids (FFAs) have based the argument on a few main points: there is an evolutionary advantage to oral fat detection; a potential fat receptor has been located on taste bud cells; fatty acids evoke specific responses that activate gustatory neurons, similar to other currently accepted tastes; and, there is a physiological response to the presence of oral fat. Although CD36 has been studied primarily in mice, research examining human subjects ability to taste fats found that those with high levels of CD36 expression were more sensitive to tasting fat than were those with low levels of CD36 expression; this study points to a clear association between CD36 receptor quantity and the ability to taste fat. Other possible fat taste receptors have been identified. G protein-coupled receptors GPR120 and GPR40 have been linked to fat taste, because their absence resulted in reduced preference to two types of fatty acid (linoleic acid and oleic acid), as well as decreased neuronal response to oral fatty acids.Monovalent cation channel TRPM5 has been implicated in fat taste as well, but it is thought to be involved primarily in downstream processing of the taste rather than primary reception, as it is with other tastes such as bitter, sweet, and savory.Proposed alternate names to fat taste include oleogustus and pinguis, although these terms are not widely accepted.
Gustducin is made of three subunits. When it is activated by the GPCR, its subunits break apart and activate phosphodiesterase, a nearby enzyme, which in turn converts a precursor within the cell into a secondary messenger, which closes potassium ion channels. Also, this secondary messenger can stimulate the endoplasmic reticulum to release Ca2+ which contributes to depolarization. This leads to a build-up of potassium ions in the cell, depolarization, and neurotransmitter release. It is also possible for some bitter tastants to interact directly with the G protein, because of a structural similarity to the relevant GPCR. Umami
Umami, or savory, is an appetitive taste. It can be tasted in soy sauce, meat, dashi and consomme. A loanword from Japanese meaning "good flavor" or "good taste", umami (旨味) is considered fundamental to many East Asian cuisines, such as Japanese cuisine. It dates back to the use of fermented fish sauce: garum in ancient Rome and ge-thcup or koe-cheup in ancient China.Umami was first studied in 1907 by Ikeda isolating dashi taste, which he identified as the chemical monosodium glutamate (MSG). MSG is a sodium salt that produces a strong savory taste, especially combined with foods rich in nucleotides such as meats, fish, nuts, and mushrooms.Some savory taste buds respond specifically to glutamate in the same way that "sweet" ones respond to sugar. Glutamate binds to a variant of G protein coupled glutamate receptors.