I'm busy with trying to write an article on my research and getting caught up on the literature. I still found time to glance at this article, published last week in Nature. Coincidentally, Alex at The Daily Transcript posted an old blog entry of his on a similar topic.
As a food chemist I am interested in how food changes during processing and storage. I like to joke that once food reaches the mouth I lose interest. Well, that isn't strictly true. The reaction I study, the Maillard Reaction, is very important in food as it causes color and flavor formation. If it goes too far it can cause the formation of burnt flavors. So I am very interested in taste preception, so this article grabbed my attention as it is about how certain compounds alter taste perception.
The article considers both the sensory, or human psychophysics as they call it, and the biological affects of sweeteners such as Na-saccharin on a human sweetener receptor cell line. Na-saccharin has been previously shown to have a sweet "water-taste" stimulus. Quotes from the article:
" 'Water-tastes' are gustatory after-impressions elicited by water following the removal of a chemical solution from the mouth, akin to colour after-images appearing in 'white' paper after fixation on coloured images."
"Saccharin is a non-caloric sweetener commonly used at low concentrations in foods and beverages. At high concentrations, however, Na-saccharin elicits little sweetness and tastes mostly bitter after consecutive exposures. When high concentrations are rinsed from the mouth, the perception switches from a primarily bitter taste to an intense sweet taste."
"It should be noted that sweet 'water-taste' does not refer to a lingering taste from rinsing a sweetener from the mouth, as the water rinses after most sweeteners taste 'barely' sweet. For each concentrated Na-saccharin solution, the intensity of sweet 'water-taste' that followed was proportional to the degree of apparent sweetness inhibition during sampling…we postulated that other sweet 'water-taste' compounds might also be sweet-taste inhibitors."
"Even when tasted alone, high concentrations of acesulfame-K and Na-saccharin self-inhibit their sweet taste, suggesting a similar mode of action for these two compounds. In contrast, Na-cyclamate, a sweetener with no sweet 'water-taste' did not inhibit sweetness when mixed with other sweeteners."
To check to see if Na-saccharin directly inhibits the human sweetener receptor, they used in vitro HEK293T cell system. I found this part harder to follow, as I am not a biologist. The results support the hypothesis that saccharin and other sweet 'water-taste' compounds inhibit the human sweetener receptor. The results also showed that these affect of the receptors response to other sweeteners. So when Na-saccharin is mixed with sucrose, for example, the receptor doesn't respond to the sucrose as it has been inhibited by Na-saccharin.
So it seems that the sweet 'water-tastes' are caused by the inhibitor being rinsed away from the sweetener receptors.
Galindo-Cuspinera, V., Winnig, M.,Bufe, B., Meyerhof, W. & Breslin, P. A. S. (2006) "A TAS1R receptor-based explanation of sweet 'water-taste'" Nature advance online publication 23 April 2006 | doi:10.1038/nature04765; Received 19 December 2005; Accepted 31 March 2006