The stevia plant

The holiday season can be a time of excess, but low- or no-calorie sweeteners could help merry-makers stay trim. Stevia is a zero-calorie sweetener that is sometimes called "natural" because it is extracted from the leaves of a South American plant. Now, a report in ACS Synthetic Biology describes a way to prepare large quantities of stevia using yeast, which would cut out the plant middleman and could lead to a better tasting product.

In the stevia plant, a series of enzymes turn glucose into molecules called glucosides that retain sugary sweetness without the calories. The plant produces a variety of glucosides, but some have a bitter aftertaste. Others are minor glucosides in the plant, but because of their pleasant properties, they could be developed into next-generation sweeteners. So, to make a sweeter sweetener and to make lots of it, Vincent J.J. Martin and colleagues wanted to take the glucoside-making machinery out of the plant and into yeast, where they could more easily tweak enzymes to optimize stevia production.

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The researchers created a platform for testing enzyme combinations to see which mixture produced the highest yield of stevia molecules in yeast. They started with the enzymes from the stevia plant, but also used some related enzymes from a plant in the mustard family, which improved yield. The authors say that their results represent a step toward the commercial production of a new generation of better-tasting no-calorie sweeteners.