Sweetener without the aftertaste

Research has found the molecular machinery behind the intense sweetness of the stevia plant, which could be used to create better tasting, non-caloric sweeteners.

Published in Proceedings of the National Academy of Sciences, researchers from Washington University in St. Louis revealed the three-dimensional structure of the proteins that make rebaudioside A (RebA), the major ingredient in the sweetener Stevia.

"Stevias and their related molecules occur naturally in plants and are more than 200 times sweeter than sugar," said lead author and Professor of Biology in Arts & Sciences, Joseph Jez. However, Stevia can cause a metallic aftertaste not associated with sugar.

The researchers used X-ray crystallography to determine the structure of the RebA protein. They explained the stevia plant consists of  "a core terpene structure decorated with a specific pattern of glucose molecules, including a branched three-sugar unit".

"RebA is abundant in the stevia plant and was the first product made from the plant because it was easy to purify in bulk. Call this 'Stevia 1.0'," Jez said. "But in the leaf are other related compounds with different structures that hit the 'sweet' without the aftertaste. Those are 'Stevia 2.0', and they will be big."

He explained how the new protein structure information could be used to help improve sweeteners.

"One could use the snapshot of the protein that makes RebA to guide protein engineering efforts to tailor the types and/or pattern of sugars in the stevias. This could be used to explore the chemical space between 'sweet' and 'yuck'.

"There are also molecules in other plants that are not 'stevias' but can deliver intense sweetness. We could use the information of how the stevia plant does it as a way of finding those details."

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