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The taste quality of steviol glycosides (SG) is highly dependent on the numbers and linkages of glucosyl units connecting to its diterpenoid core. In this work, the transglycosylation of stevioside (ST) catalyzed by cyclodextrin glucanotransferase were optimized initially. At a high conversion rate of ~ 65%, a mixture of ST derivatives was produced by adding 1– 6 glucosyl units to the ST molecule. By further treatment with α-glucosidase for 4– 24 h, the length of the glucosyl chain can be reduced to 1– 2 units. Based on a previous investigation, the SG recovered from the mother liquor of stevia production was used as the substrate. Taste quality evaluation on the obtained glucosyl steviol glycosides (GSG) suggested both the sweet and bitter aftertaste were significantly weakened after transglycosylation. The sweetness of GSG was obviously reduced with the increase in glucosyl-chain length, while the licorice flavor caused by the residual polyphenols can also be weakened after enzymatic modification. The GSG products presented unique taste quality different from rebaudioside A (RA) and rebaudioside M (RM), while their overall taste quality was close to that of RM. Conclusively, the research can provide a clean approach to promote the resource utilization of stevia, and new GSG products with improved taste quality can be the potential sweetener for food manufacture.

This study addresses the favourable effects of drought stress imposed by polyethylene glycol (PEG) 6000 on the micropropagated shoots of Stevia rebaudiana. Various concentrations, i.e., 0, 0.5, 1, 2, and 4% of PEG 6000 were applied to the nodal shoot explants for four weeks, and the influence produced on shoots growth parameters, bioactive steviol glycosides (rebaudioside A and stevioside), and nonenzymatic antioxidant activities (total phenolic content (TPC), total flavonoid content (TFC), total antioxidant capacity (TAC), total reducing power (TRP) and 1,1-diphenyl-2-picrylhydrazyl(DPPH)-free radical scavenging activity (FRSA)) was elucidated. The significantly highest yield (92.4% direct shoot organogenesis) and secondary metabolites (2.94% Reb A, 2.52% ST, 95.3% DPPH-FRSA, 15.0% TPC, 13.0 µg/mg TFC, 22.3 µg/mg TAC, and 19.8 µg/mg TRP) production in response to abiotic stress elicitors was obtained in Murashige and Skoog (MS) medium treatment provided with 4% of PEG 6000. The overall trend was significant enhancement of growth dynamics and pharmaceutical compounds from control to 4% of PEG 6000 concentration as a defensive response against reactive oxygen species (ROS) produced in excess by water deficit. This is a very promising study to be employed in bioreactors to get markedly enhanced content of compounds of medicinal importance in the pharmaceutical market.

Steviol glycosides (SvGls) are plant secondary metabolites belonging to a class of chemical compounds known as diterpenes. SvGls have been discovered only in a few plant species, including in the leaves of Stevia rebaudiana Bertoni. Over the last few decades, SvGls have been extensively researched for their extraordinary sweetness. As a result, the nutritional and pharmacological benefits of these secondary metabolites have grown increasingly apparent. In the near future, SvGls may become a basic, low-calorie, and potent sweetener in the growing natural foods market, and a natural anti-diabetic remedy, a highly competitive alternative to commercially available synthetic drugs. Commercial cultivation of stevia plants and the technologies of SvGls extraction and purification from plant material have already been introduced in many countries. However, new conventional and biotechnological solutions are still being sought to increase the level of SvGls in plants. Since many aspects related to the biochemistry and metabolism of SvGls in vivo, as well as their relationship to the overall physiology of S. rebaudiana are not yet understood, there is also a great need for in-depth scientific research on this topic. Such research may have positive impact on optimization of the profile and SvGls concentration in plants and thus lead to obtaining desired yield. This research summarizes the latest approaches and developments in SvGls production.Key points• Steviol glycosides (SvGls) are found in nature in S. rebaudiana plants.• They exhibit nutraceutical properties.• This review provides an insight on different approaches to produce SvGls.• The areas of research that still need to be explored have been identified.

Understanding the edulcorant profile of synthetic glucosyl steviol glycosides (GSGs) and rare natural steviol glycosides (SGs) is challenging due to their numerous species and rareness. This study developed a computational model based on the interactions of SG molecules with human sweet and bitter taste receptors (hSTR/hBTR). The models demonstrated a high correlation between the cumulative interaction energies and the perceived sweetness of SGs (R2 = 0.97), elucidating the mechanism of the diverse sweetness of SGs. It also revealed that more (within three) glucose residues at the C-13 position of the SG molecule yield stronger sweetness and weaker bitterness. Furthermore, the computational prediction was consistently validated with the known sweetness of GSG and also aligned well with that of several natural mogrosides. Thus, this model possesses a potential to predict the sweetness of SGs, GSGs, and mogrosides, facilitating the application or targeted synthesis of GSGs with desired sensory profiles.

There has been a challenge in overcoming the bitter aftertaste of stevia, a natural non-caloric sweetener. Recent research focuses on investigating various types of steviol glycosides, the sweet compounds in stevia leaves, as they exhibit different sensory characteristics. This study determined the sensory properties and acceptability of ice cream sweetened solely with three steviol glycosides, rebaudioside (Reb) A, D, and M (0.09% w/v), using sucrose-sweetened ice cream as a control (14% w/v). Ice cream consumers (n = 92) rated their overall liking, attribute liking, and sweetness and bitterness intensities and described the aftertastes of each sample using check-all-that-apply. The liking scores of Reb D- and M-sweetened ice creams were significantly higher than those of Reb A-sweetened ice cream. Among the three glycosides, only Reb M showed a sweetness intensity comparable with that of sucrose. Consumers perceived the aftertastes of Reb D and M ice creams as being more sweet, pleasant, creamy, and milky, while Reb A was more artificial and chemical. Reb D and M ice creams were also plotted close to sucrose in the correspondence analysis graph, meaning that their aftertaste characteristics were similar to those of sucrose. The present study clearly highlights that Reb D and M have better tastes and provide better perceptions to consumers than Reb A, which is the most widely used glycoside in food industry.

Rebaudioside E, one of the minor components of steviol glycosides, was first isolated and identified from Stevia rebaudiana in 1977. It is a high-intensity sweetener that tastes about 150–200 times sweeter than sucrose and is also a precursor for biosynthesis of rebaudioside D and rebaudioside M, the next-generation Stevia sweeteners. In this work, new unknown steviol glycosides were enzymatically synthesized from stevioside by coupling UDP-glucosyltransferase UGTSL2 from Solanum lycopersicum and sucrose synthase StSUS1 from Solanum tuberosum. Rebaudioside E was speculated to be the main product of glucosylation of the Glc(β1→C-19) residue of stevioside along with the formation of a (β1→2) linkage based on the analysis of the regioselectivity and stereoselectivity of UGTSL2, and verified afterwards by LC-MS/MS with standard. In a 20-ml bioconversion reaction of 20 g/l stevioside by UGTSL2 and StSUS1, 15.92 g/l rebaudioside E was produced for 24 h.

The enzymatic transglycosylation of steviol glycosides can improve the edulcorant quality of steviol glycosides. Cyclodextrin glucanotransferase (CGTase) is one of the most popular glucanotransferases applied in this reaction. Herein, the CGTase-producing strain Alkalihalobacillus oshimensis CGMCC 23164 was isolated from Stevia planting soil. Using mass spectrometry-based secretome profiling, a high-efficiency CGTase that converted steviol glycosides to glucosylated steviol glycosides was identified and termed CGTase-13. CGTase-13 demonstrated optimal transglycosylation activity with 10 g/L steviol glycoside and 50 g/L soluble starch as substrates at <40 °C. Under the above conditions, the conversion rate of stevioside and rebaudioside A, two main components of steviol glycosides, reached 86.1% and 90.8%, respectively. To the best of our knowledge, this is the highest conversion rate reported to date. Compared with Toruzyme® 3.0 L, the commonly used commercial enzyme blends, glucosylated steviol glycosides produced using CGTase-13 exhibited weaker astringency and unpleasant taste, faster sweetness onset, and stronger sweetness intensity. Thus, CGTase provides a novel option for producing high-quality glucosylated steviol glycoside products and has great potential for industrial applications.

With the pursuit of natural non-calorie sweeteners, steviol glycosides (SGs) have become one of the most popular natural sweeteners in the market. The SGs in Stevia are a mixture of SGs synthesized from steviol (a terpenoid). SGs are diterpenoids. Different SGs depend on the number and position of sugar groups on the core steviol backbone. This diversity comes from the processing of glycoside steviol by various glycosyltransferases. Due to the differences in glycosylation, each SG has unique sensory properties. At present, it is more complicated to extract high-quality SGs from plants, so the excavation of the metabolic pathways of engineered microorganisms to synthesize SGs has been extensively studied. Specifically, the expression of different glycosyltransferases in microbes is key to the synthesis of various SGs by engineered microorganisms. To trigger more researches on the functional characterization of the enzymes encoded by these genes, this review describes the latest research progresses of the related enzymes involved in SG biosynthesis and metabolic engineering.Key points• Outlines the research progress of key enzymes in the biosynthetic pathway of SGs• Factors affecting the catalytic capacity of stevia glucosyltransferase• Provide guidance for the efficient synthesis of SGs in microbial cell factories

Steviol glycoside sweeteners have been isolated and produced for hundreds of years in Bertoni, a South American Asteraceae plant prized for its sweetness. Stevia is becoming more popular among consumers and food manufacturers as a result of diabetes, rising obesity rates, and other related comorbidities, as well as global public policies calling for a reduction in intake of sugar to help control these issues. Low-calorie as well as no-calorie sweeteners, such as Stevia, have this appeal because they are plant-based, have no calories, and have a sugary flavour that is 50 to 350 times sweeter than table sugar, making them an excellent as well as suitable choice for use in foods as well as beverages with lower sugar and calorie content. This plant yields steviol glycoside sweeteners, which are isolated and processed. Current studies on Stevia rebaudiana extract, metabolism, tolerable intake, and safety, steviol glycoside extraction and purification, side effects, as well as the toxicity of Stevia extract are discussed in detail.

This literature-based review synthesizes the available scientific information about steviol glycosides as natural sweeteners and molecules with therapeutic potential. In addition, it discusses the safety concerns regarding human consumption. Steviol glycosides exhibit a superior sweetener proficiency to that of sucrose and are noncaloric, noncariogenic, and nonfermentative. Scientific evidence encourages stevioside and rebaudioside A as sweetener alternatives to sucrose and supports their use based on their absences of harmful effects on human health. Moreover, these active compounds isolated from Stevia rebaudiana possess interesting medicinal activities, including antidiabetic, antihypertensive, anti-inflammatory, antioxidant, anticancer, and antidiarrheal activity. The described bioactivities of steviol glycosides deserve special attention based on their dose dependence and specific pathological situations. Further clinical research is needed to understand underlying mechanisms of action, therapeutic indexes, and pharmacological applications.