Gymnemic acids sweetness-suppressing

The leaves of the tropical plant Gymnema sylvestre, when chewed, suppress the ability to taste sweetness. The effect lasts for hours, and sugar seems like sand in the mouth. The ability to taste other sweeteners such as saccharin is equally suppressed. There is also a decrease in the ability to taste bitterness. The active principle of leaves has been named gymnemic acid and has been found (Stocklin et al. 1967) to consist of four components, designated as gymnemic acids, Ab A2, A3, and A4. These are D-glucuronides of acety-... 

The sweetness-inhibiting substance ziziphin was isolated from the leaves of the plant Zizyphus jujuba (Rhamnaceae), which is native to China, by Kurihara et al 1 Like gymnemic acids, ziziphin is a glycoside of triterpene that suppresses sweetness in humans. Removal of the acyl group under mild hydrolytic conditions led to complete abolishment of its antisweet activity. 

A substance isolated from the Indian shrub Gymnema sylvestre, has a profound ability to reduce perceived sweetness of sugar solutions. The effect was noticed over a century ago when two British inhabitants of an Indian village found that, after chewing the leaves of G sylvestre, the sweetness of their tea disappeared (7). The sweetness suppressing activity is due to a mixture of several triterpene saponins which have collectively been termed the gymnemic acids. For most people exposed to the effects of GA, sweetness suppression is complete and the effect lasts for about an hour. 

Once a purified gymnemic acid became available, much psychophysical work was done to understand the nature of the sweetness inhibition effect. The work of Bartoshuk and co-workers illustrates the course taken (15). The results of a typical experiment are shown in Figure 3. The sweetness of a sucrose solution was almost completely suppressed after holding a gymnemic acid solution in the mouth for a few seconds. Further experiments were carried out to determine the effect of gymnemic acid on the other taste qualities (sour, bitter and salty). No effect of gymnemic acid on these tastes was observed. Early work with GA extracts had produced an apparent inhibition of bitter taste, but this effect was later attributed to cross-adaptation to the taste of the crude leaf extract, which was itself quite bitter. Experiments with refined (and tasteless) extracts showed no bitterness suppression. 

The suppression of sweetness by gymnemic acids and the effects on glucose... 

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