Taste Perception: Cracking the Code

T he ability to taste food is a life-and-death matter. Failure to recognise food with a high enough caloric content could mean a slow death from malnutrition. Failure to detect a poison could result in near-instant expiration. And now, as researchers begin to understand some of the nuts and bolts of taste perception, it seems that the sense of taste may also have more subtle effects on health. At the front line of the taste sensory system are the taste buds—onion-shaped structures on the tongue and elsewhere in the mouth (Figure 1). Up to 100 taste receptor cells—epithelial cells with some neuronal properties— are arranged in each taste bud. In the tongue, the taste buds are innervated by the chorda tympani (a branch of the facial nerve) and the glossopharyngeal nerve. These nerves carry the taste messages to the brain. Taste is the sense by which the chemical qualities of food in the mouth are distinguished by the brain, based on information provided by the taste buds. Quality or 'basic taste', explains Bernd Lindemann, now retired but an active taste researcher in Germany for many years, is a psychophysical term. Large numbers of people describe different tastants and then statistical analyses are used to defi ne the important tastes. 'The number of taste qualities has varied over the years', says Lindemann. 'We are now settling at around fi ve, though I would not be surprised if some additional qualities pop up'. The fi ve qualities that Lindemann refers to are salty, sour, bitter, sweet, and umami, the last being the Japanese term for a savoury sensation. Salty and sour detection is needed to control salt and acid balance. Bitter detection warns of foods containing poisons— many of the poisonous compounds produced by plants for defence are bitter. The quality sweet provides a guide to calorie-rich foods. And umami (the taste of the amino acid glutamate) may fl ag up protein-rich foods. Our sense of taste has a simple goal, explains Lindemann: 'Food is already in the mouth. We just have to decide whether to swallow or spit it out. It's an extremely important decision, but it can be made based on a few taste qualities'. Taste has been actively researched for many decades. During the 20th century, electrophysiologists and other researchers worked hard to understand this seemingly simple sense system. Then, in 1991, the fi rst olfactory receptors were described. …