Your tongue holds a few thousand taste buds, small clusters of cells, most of them in the bumps on its surface. Their receptors and channels pick up five tastes, and taste buds all over the tongue pick up all five.
| Taste | What the taste cells pick up | Found in |
|---|---|---|
| sweet | sugars such as sucrose and fructose | fruit, honey, cake |
| sour | H⁺ from acids | lemons, vinegar, yoghurt |
| salty | sodium ions, Na⁺, from salt | crisps, olives, soy sauce |
| bitter | many molecules, picked up by about 25 kinds of bitter receptor | coffee, dark chocolate, tonic water |
| umami | glutamate, from the amino acid glutamic acid | tomatoes, parmesan, mushrooms |
Sour is the taste of acid. H⁺ from an acid passes into sour taste cells through a channel made for it, and the cells signal to your brain. The more H⁺, the more sour: lemon juice, at about pH 2, has about 30 times the H⁺ of orange juice, at about pH 3.5, and tastes far sourer.
Umami is a Japanese word for a savoury taste. The chemist Kikunae Ikeda named it in 1908, after he traced the taste of a broth made with kombu seaweed to glutamic acid. In food it is mostly glutamate, the ion glutamic acid becomes once it has given away H⁺ from one of its two -COOH groups.
Sweeter than sugar
The sweet receptor is a protein with a pocket, like every other receptor in this lesson. Sucrose fits it, and some molecules fit it so much better that a pinch of them tastes as sweet as a spoonful of sugar.
Aspartame is built from two amino acids, L-aspartic acid and L-phenylalanine, joined by the same peptide bond that joins the amino acids in a protein. The phenylalanine end is an ester, with a methyl group in place of the H of its -COOH. A chemist found its sweet taste by chance in 1965, when he licked his finger to pick up a sheet of paper.
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| Sweetener | Times as sweet as sucrose |
|---|---|
| aspartame | about 200 |
| acesulfame K | about 200 |
| saccharin | 200 to 700 |
| sucralose | about 600 |
| advantame | about 20,000 |
So little sweetener is needed that it adds almost no energy to a drink. Sucralose is made from sucrose itself: three of its -OH groups are swapped for chlorine atoms.
Quick check
That's the end of lesson 27
In this lesson you found out:
- How smell receptors turn molecules into patterns your brain reads
- Why some mirror-image pairs smell different and others smell the same
- Why chilli feels hot and menthol feels cold
- What the five tastes pick up, and why sweeteners are needed in such small amounts