Making Sweeter Natural Sweeteners with Yeast and Enzymes

Greg Howard
4th April, 2024

Making Sweeter Natural Sweeteners with Yeast and Enzymes

Image Source: Natural Science News, 2024

Key Findings

  • At Jiangnan University, scientists improved the production of a low-calorie sweetener, Reb M, using modified yeast
  • They increased Reb M yield to 12.5g/L, the highest reported, by altering genes in the yeast
  • The study's methods could lead to a variety of new, natural sweeteners for health-conscious consumers
In the realm of natural sweeteners, the quest for healthier sugar alternatives has led to a significant scientific breakthrough at Jiangnan University. Researchers have honed in on a natural sweetener called Rebaudioside M (Reb M), a compound that has garnered attention for its high sweetness and minimal caloric content. The study[1] focused on enhancing the production of Reb M using the yeast Saccharomyces cerevisiae, a common microorganism used in biotechnology. Reb M is found in the plant Stevia rebaudiana, which has been a source of interest due to its naturally sweet compounds known as steviol glycosides (SGs)[2]. These compounds, including Reb M, have become popular as sugar substitutes because they do not contribute calories to the diet and are much sweeter than sugar. However, the content of Reb M in Stevia plants is low, and previous attempts to produce Reb M in microorganisms have been limited by low efficiency[3]. The Jiangnan University study aimed to tackle this problem by genetically engineering S. cerevisiae to convert another steviol glycoside, stevioside, into Reb M more effectively. The researchers first removed a gene in the yeast responsible for breaking down glycosides, which are sugar molecules that contribute to the sweetness of SGs. By knocking out the SCW2 gene, they prevented the degradation of the desired product. Next, they focused on the glycosylation process, which is the addition of sugar molecules to the steviol backbone of SGs. This step is crucial as it determines the sweetness and sensory properties of the end product. By screening different glycosyltransferases, enzymes that attach sugar molecules to other compounds, they found that UGT91D2 from Stevia was the most efficient for this purpose[2]. To further enhance the sweetness of Reb M, the researchers overexpressed a gene, UGP1, to increase the supply of UDP-glucose, the sugar donor molecule needed for glycosylation. They also co-expressed UGT91D2 with another glycosyltransferase, UGT76G1, to achieve a more efficient conversion of stevioside to Reb M[2]. One of the innovative aspects of this study was the introduction of the silencing information regulator 2 (SIR2) into the yeast. SIR2 is known to extend the lifespan of yeast cells, and by doing so, it prolonged the growth cycle of the engineered S. cerevisiae, allowing for a longer period of Reb M production. The culmination of these genetic modifications resulted in the production of 12.5 grams of Reb M per liter in a 5-liter bioreactor, starting with 10 grams of stevioside. This yield of 77.9% represents the highest reported conversion of steviol glycosides to Reb M, a significant leap forward for the industrial production of this sweetener. The importance of this study is underscored by previous research that has identified the potential of steviol glycosides as natural, low-calorie sweeteners[3]. The sensory properties of these compounds, such as sweetness onset, intensity, and aftertaste, are critical for consumer acceptance[4]. For instance, it has been shown that the addition of glucosyl groups to certain positions on the steviol backbone can reduce bitterness and enhance sweetness[4]. The work at Jiangnan University has built upon this knowledge by optimizing the glycosylation process to produce a sweetener with desirable sensory characteristics. This research not only paves the way for more accessible natural sweeteners but also provides a framework for producing other steviol glycosides. The methods developed could be applied to synthesize different SGs with unique sensory profiles, potentially expanding the range of natural sweeteners available to consumers concerned about sugar intake. The success of this study from Jiangnan University is a testament to the power of biotechnological innovation in addressing global health concerns. By harnessing the capabilities of microorganisms and the precise tools of genetic engineering, scientists are unlocking new possibilities for healthier food ingredients. The engineered yeast strain and the strategies developed here offer a promising solution to the challenges of producing natural sweeteners at a scale that meets the growing demand for sugar alternatives.



Main Study

1) Efficient Conversion of Stevioside to Rebaudioside M in Saccharomyces cerevisiae by a Engineering Hydrolase System and Prolonging the Growth Cycle.

Published 2nd April, 2024

Related Studies

2) Metabolic engineering for the synthesis of steviol glycosides: current status and future prospects.

3) Biotechnological production of natural zero-calorie sweeteners.

4) Dynamic characteristics of sweetness and bitterness and their correlation with chemical structures for six steviol glycosides.

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