Thaumatin is a low-calorie (virtually calorie-free) protein sweetener and flavour modifier. The substance is often used primarily for its flavour modifying properties and not exclusively as a sweetener.
The thaumatins were first found as a mixture of proteins isolated from the katemfe fruit (Thaumatococcus daniellii Bennett) of west Africa. Some of the proteins in the thaumatin family (Simple Modular Architecture Research Tool accession #SM00205) are natural sweeteners roughly 2000 times more potent than sugar. Although very sweet, thaumatin's taste is markedly different from sugar's. The sweetness of thaumatin builds very slowly. Perception lasts a long time leaving a liquorice-like aftertaste at high usage levels. Thaumatin is highly water-soluble, and stable to heating and stable under acidic conditions.
Like other PR proteins, thaumatin is predicted to have a mainly beta structure, with a high content of beta-turns and little helix. Tobacco cells exposed to gradually increased salt concentrations develop a greatly increased tolerance to salt, due to the expression of osmotin, a member of the PR protein family. Wheat plants attacked by barley powdery mildew express a PR protein (PWIR2), which results in resistance against that infection. The similarity between this and other PR proteins to the maize alpha-amylase/trypsin inhibitor has suggested that PR proteins may act as some form of inhibitor.
Thaumatin-like protein has been found in olive fruit, and it can cause allergic reactions. A worker in an olive-oil mill in Jaen, Spain had respiratory symptoms at work. His blood serum was used to extract a 23 kilodalton protein from olive pulp, which was purified and confirmed to cause an allergic reaction in a skin prick test. The protein had amino acid sequence ATFXIVNQXTYTVXAAASP which was similar (homologous) to thaumatin-like proteins.
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