Five basic tastes are only the opening act of flavour
Taste begins when chemicals meet receptor cells in buds clustered on tongue papillae—and also on palate, cheeks, and throat. Humans host roughly two to five thousand buds, each packing fifty to one hundred sensors, yet smell, texture, temperature, and chemesthesis finish what we call flavour.
Five primary qualities are sweet, sour, salty, bitter, and umami. Sweet, bitter, and savory signals ride G protein-coupled receptors; salt and sour track ions such as sodium and hydrogen. Western physiology long counted only four tastes until Japanese work on savoriness, named umami by Kikunae Ikeda, entered the consensus. Filiform papillae lack buds even as nearby bumps carry hundreds.
Ecology explains the palette: sweetness flags calorie-dense sugars, bitterness often warns of toxins, salt supports ion balance, sour can mark spoilage or damaging acids, and umami tracks amino acids such as glutamate needed for proteins and enzymes. Cats cannot detect sweetness; some carnivores lost several ancestral tastes; certain rodents sense starch humans miss.
Age dulls perception as papillae thin and saliva fades, and dysgeusia can warp signals. Artificial sweeteners hijack the same GPCR–gustducin pathway that sucrose uses at about a ten millimole-per-litre detection threshold. Flavour is therefore a negotiation among gustation, olfaction, and trigeminal nerves—not a tongue map of isolated zones.
Some of the machinery was pinned down only recently. Sour detection runs through a small population of Type III cells, where protons pour in via a channel identified in 2018 as otopetrin 1. Saltiness appears to split into a pleasant low-salt signal, carried by the epithelial sodium channel, and a harsher high-salt signal whose receptor is still unknown. The drug amiloride blocks the low-salt route strongly in rats but only weakly in people, hinting at undiscovered receptors. Potassium chloride, the usual salt substitute, scores 0.6 against table salt. The list of basics may yet grow: pungency was once treated as a sixth taste, and in 2015 researchers proposed a fat taste, sometimes called oleogustus.
Source: Taste
