The study – published in the Journal of Agricultural and Food Chemistry – characterized the sensory properties of the most common stevia compounds (steviol glycosides) in a new way by combining human taste panel studies with cell-based taste receptor assays to assess how compounds are sensed on the tongue.
Led by Professor Thomas Hofmann from the Technical University Munich (TUM) and his colleagues at the German Institute of Human Nutrition Potsdam-Rehbruecke (DIfE), the new study identifies two receptors (hTAS2R4 and hTAS2R14) that are responsible for the detection of the bitter taste notes of the recently approved natural sweetener.
Hofmann and his team noted that the human tongue has just one receptor type for detecting sweetness but about 25 different ones for bitter flavors.
“Steviol glycosides activate two bitter receptors on the human tongue, and this elicits a bitter after taste in the mouth,” explained Anne Brockhoff, a co-author of the study – based at DIfE.
Hoffman said the findings could help manufacturers minimise the bitter taste of stevia products at an early stage in production processes. ”They could open the way for selective cultivation measures or targeted purification during the development of Stevia products, enabling manufacturers to focus on the sweetest candidates,” said the project leader.
Stevia is regarded by many as a healthy alternative to sugar. However, Hoffman and his team noted that there are drawbacks to many of the products made using the sweetener.
One such problem is a long-lasting bitter after-taste – which produces liquorice-like aromas and a bitter after taste.
The German scientists investigated nine steviol glycosides responsible for the intensive sweet taste of stevia extracts. The team initially tested the bitterness and sweetness that each glycoside produces in vitro – using cells that act as taste receptor cells and react to the glycoside molecules like an artificial tongue.
The team were therefore able to identify the receptors that are activated by stevia.
Hoffman and his colleagues also tested the taste intensity of different concentrations of stevia components with a trained tasting panel. The results of those sensory tests combined with the initial cell experiments revealed that the structure of glycoside molecules plays a key role in determining sweetness or bitterness in stevia, said the project leader.
“If a molecule has more glucose molecules attached to it, it is sweeter and less bitter,” he explained.
The ‘comprehensive’ screening also revealed two receptors, hTAS2R4 and hTAS2R14, mediate the bitter off-taste of steviol glycosides.
“These results might contribute to the production of preferentially sweet and least bitter tasting Stevia extracts by an optimization of breeding and post-harvest down-stream processing,” explained the German team.
Source: Journal of Agricultural and Food Chemistry
Published online ahead of print, doi: 10.1021/jf301297n
“Human Psychometric and Taste Receptor Responses to Steviol Glycosides”
Authors: C. Hellfritsch, A. Brockhoff, F. Staehler , W. Meyerhof, T. Hofmann