What makes stevia 200 times sweeter than sugar?

A new study from the University of Washington in St. Louis reveals the molecular mechanisms underlying the intense sweetness of the stevia plant. The results could be used to design new non-caloric products without the after-taste that many associate with a sweetener marketed as Stevia.

Although the genes and proteins of the biochemical pathway responsible for the synthesis of stevia are almost completely known, it is the first time that the three-dimensional structure of the proteins that make rebaudioside A – or "RebA", the 39; main ingredient of the product Stevia- has been published, according to the authors of a new document in the Proceedings of the National Academy of Sciences.

"If a person is diabetic or obese and has to eliminate sugar from their diet, they can turn to artificial sweeteners based on chemical synthesis (aspartame, saccharin, etc.), but all have atypical tastes not associated with sugar. , and some have their own health issues, "said Joseph Jez, professor of biology at Arts and Sciences and senior author of the new study.

"Stevia and its associated molecules are naturally present in plants and are more than 200 times sweeter than sugar," he said. "They have been consumed for centuries in Central and South America and are safe for consumers, and many large food and beverage companies are looking to the future and trying to reduce the number of calories / sugar in various projects over the next few years, in order to meet the demands of consumers around the world. "

The researchers determined the structure of the RebA protein by X-ray crystallography. Their analysis shows how RebA is synthesized by a key plant enzyme and how the chemical structure required for this high-intensity sweetness is biochemically constructed.

To make something 200 times sweeter than a glucose molecule, the plant enzyme decorates a terpene scaffold with three special sugars.

This extra-sweet taste of the stevia plant, however, has a disadvantage in terms of undesirable taste.

"For me, the sweetness of Stevia comes with a lint-like aftertaste of aluminum foil," said Jez. Many consumers experience this slightly metallic aftertaste.

"The taste is particular to the predominant molecules in the leaf of the plant: stevioside and RebA," he said. "It's their chemical structure that strikes the taste receptors on the tongue that triggers the" sweet ", but they also strike other taste receptors that trigger other tastes."

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

Recently published information on protein structure could be used to improve sweeteners.

"One could use the snapshot of the protein that RebA manufactures to guide protein engineering efforts to adapt the types and / or configuration of sugars in stevia," Jez said. "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 that can deliver intense sweetness," he said. "We could use the information on how the stevia plant does it to find these details."