The Interplay Between Sweet and Bitter

In contrast to umami, which in its pure form is brought out by only a small number of substances, an incredible range of very diverse substances brings out sweetness and bitterness. For a long time, it was thought that the receptors for sweet and bitter tastes were very closely related. This is due to the fact that many sweet substances, such as the artificial sweetener saccharine, can have a bitter aftertaste. In addition, only very minor chemical modifications can change a molecule from sweet tasting to bitter tasting. Mirror images of molecules can actually have sweet and bitter tastes, respectively. For example, the artificial sweetener aspartame, which is made up of two amino acids, tastes sweet if the amino acids are left turning. But if the same molecule contains right-turning amino acids instead, it will have a bitter taste.