The chemosensory basis for detecting sweetness, which varies among both individuals and species, has only been teased apart in recent years. The current theoretical model is the multipoint attachment theory, which involves multiple binding sites between sweetness receptor and the sweet substance itself.

Examples of sweet substances

A great diversity of chemical compounds, such as aldehydes and ketones are sweet. Among common biological substances, all of the simple carbohydrates are sweet to at least some degree. Sucrose (table sugar) is the prototypical example of a sweet substance, although another sugar, fructose, is somewhat sweeter. Some of the amino acids are mildly sweet: alanine, glycine, and serine are the sweetest. Some other amino acids are perceived as both sweet and bitter.

A number of plant species produce glycosides that are many times sweeter than sugar. The most well-known example is glycyrrhizin, the sweet component of licorice root, which is about 30 times sweeter than sucrose. Another commercially important example is stevioside, from the South American shrub Stevia rebaudiana. It is roughly 250 times sweeter than sucrose. Another class of potent natural sweeteners are the sweet proteins such as thaumatin, found in the West African katemfe fruit. Hen egg lysozyme, an antibiotic protein found in chicken eggs, is also sweet.

Sweetness of various compounds

Even some inorganic compounds are sweet, including beryllium chloride and lead acetate. The latter may have contributed to lead poisoning among the ancient Roman aristocracy: the Roman delicacy sapa was prepared by boiling soured wine (containing acetic acid) in lead pots.

Hundreds of synthetic organic compounds are known to be sweet. The number of these that are legally permitted as food additives is, however, much smaller. For example, chloroform, nitrobenzene, and Ethylene glycol are sweet, but also toxic. As of 2005, seven artificial sweeteners are in widespread use: saccharin, cyclamate, aspartame, acesulfame potassium, sucralose, alitame, and neotame. Cyclamate was banned for a short period in the US, and a similar situation occurred in Canada with saccharin.

Sweetness modifiers

Two natural products have been documented to have similar sweetness-inhibiting properties: gymnemic acid, extracted from the leaves of the Indian vine Gymnema sylvestre and ziziphin, from the leaves of the Chinese jujube (Ziziphus jujuba).Kurihara, Y. 1992. Characteristics of antisweet substances, sweet proteins, and sweetness-inducing proteins. Crit. Rev. Food Sci. Nutr. 32:231-252. Gymnemic acid has been widely promoted within herbal medicine as a treatment for sugar cravings and diabetes mellitus.