Temperature-dependent solubility of Rebaudioside A in methanol/ethanol and ethyl acetate mixtures:Experimental measurements and thermodynamic modeling

The equilibrium solubility of Rebaudioside A(Reb A)FormⅡin binary mixtures of methanol/ethanol and ethyl acetate was quantitatively determined within the temperature range of 283.15—328.15 K at ambient pressure.The experimental findings indicate a positive correlation between the solubility of Reb A(FormⅡ)and both the temperature and the methanol/ethanol content in the solvent system.To describe the solubility data,six distinct models were employed:the modified Apelblat equation,theλh model,the combined nearly ideal binary solvent/Redlich—Kister(CNIBS/R—K)model,the van't HoffJouyban-Acree(VJA)model,the Apelblat-Jouyban-Acree(AJA)model,and the non-random two-liquid(NRTL)model.The combined nearly ideal binary solvent/Redlich—Kister model exhibited the most precise fit for solubility in methanol+ethyl acetate mixtures,reflected by an average relative deviation(ARD)of 0.0011 and a root mean square deviation(RMSD)of 12×10^(-7).Conversely,for ethanol+ethyl acetate mixtures,the modified Apelblat equation provided a superior correlation(ARD=0.0014,RMSD=4×10^(-7)).Furthermore,thermodynamic parameters associated with the dissolution of Reb A(FormⅡ),including enthalpy,entropy,and the Gibbs energy change,were inferred from the data.The findings underscore that the dissolution process is predominantly endothermic across the solvent systems examined.Notably,the entropy changes appear to have a significant influence on the Gibbs free energy associated with the dissolution of Reb A(FormⅡ),suggesting that entropic factors may play a pivotal role in the studied systems.

高效液相色谱法测定甜叶菊中Stevioside和Rebaudioside A的含量

建立高效液相色谱法测定甜叶菊中甜菊甙（Stevioside）和莱鲍迪甙A（Rebaudioside A）的含量。色谱条件：色谱柱为Agilent ZORBAX NH2 4．6×250mm 5μm；流动相为乙腈-pH3．0磷酸溶液（80：20）；流速1．0mL·min^-1；检测波长210nm；柱温40℃；进样量20μL。线性范围为0．1268～2．0456mg·mL^-1（r=1），加标平均回收率为98．16％，RSD为0．80％（n=6）。本方法准确度高、精密度高、重复性好、简捷易操作，可以作为甜叶菊中甜菊甙和莱鲍迪甙A含量的测定方法。

Rapid HPLC Method for Determination of Rebaudioside D in Leaves of Stevia rebaudiana Bertoni Grown in the Southeast of Mexico

Stevia leaves contain glycosides on which biological activity and sweetening capacity has been reported. Besides the main glycosides—stevioside and rebaudioside A—there are minor glycosides that may contribute to the activity and thus it is important to quantify them. Rebaudioside D is one of the minor glycoside present in S. rebaudiana leaves and there are no reports of a validated method to quantify it. Therefore a simple and sensitive high performance liquid chromatography (HPLC) method was validated for the determination of rebaudioside D in leaves of Stevia rebaudiana B. grown in the southeast of México. HPLC method was performed using a C18 column (250 mm × 4.6 mm, 5 μm) and UV detector set at 210 nm. The mobile phase consisted of 32:68 (v/v) mixture of acetonitrile and sodium phosphate buffer (10 mmol/L, pH 2.6), set to a flow rate of 1.0 ml/min. The calculated parameters were: sensitivity, linearity, limit of detection (LOD), limit of quantification (LOQ), accuracy and precision. The retention time of rebaudioside D was found to be 3.47 min ± 0.04 (S.D.). The calibration curves were linear over the working range (25 - 150 μg/ml), with correlation coefficient ≥0.99 and determination coefficient ≥0.98. The calculated limit of detection (LOD) was 8.53 μg/ml, while the limit of quantitation (LOQ) was 25.85 μg/ml. The percent recoveries of fortified samples were 100% ± 10% and precision relative standard deviation was ≤2.79%. The criteria of validation showed accuracy, linearity, and precision;therefore the method is suitable for quantitative analysis of rebaudioside D in Stevia rebaudiana leaves. Rebaudioside D content (g/100g) in Morita II and Criolla varieties grown in the southeast of Mexico were 0.43 and 0.46, respectively with no significant differences (p > 0.05) between them.

Determination of Rebaudioside A and Stevioside in Leaves of S.rebaudiana Bertoni Grown in Mexico by a Validated HPLC Method

Stevia rebaudiana is a plant with high sweetening capacity due to its content of glycosides, mainly stevioside and rebaudioside A. Several techniques have been used to determine the concentrations of glycosides in Stevia, although an HPLC method is recommended by the FAO/WHO-JECFA. Varieties of Stevia have been recently grown in Mexico, with no previous report of glycosides by a validated method. The aim of this study was to validate an isocratic HPLC method for content determination of main glycosides in the leaves of Stevia cultivated in Mexico. HPLC method was performed using a C18 column (250 mm × 4.6 mm, 5 μm) and UV detector set at 210 nm. The mobile phase consisted of 32:68 (v/v) mixture of acetonitrile and sodium-phosphate buffer (10 mmol/L, pH 2.6), set to a flow rate of 1.0 mL/min. Rebaudioside A and stevioside were determined in two Stevia varieties: Morita II and Criolla, and also validation parameters were calculated. Rebaudioside A content (g/100g) in Morita II was 15.15 ± 0.02 while stevioside was 3.97 ± 0.003;in the case of Criolla they were 4.03 ± 0.01 and 8.80 ± 0.14, respectively (p < 0.001). The recoveries of fortified samples were 100% ± 10% and precision RSD was ≤6.27%. The criteria of validation showed accuracy, linearity (≥0.99), and precision;therefore, the determination of glycosides was performed with reliability.

Enrichment and separation of rebaudioside A from stevia glycosides by a novel adsorbent with pyridyl group

The adsorptive capacity and selectivity of a novel adsorbent with pyridyl group toward stevia glycosides were studied. The effect of polarity and physical structure of the sorbent on the selectivity was investigated in detail. Two separation methods were applied in the enrichment of rebaudioside A(RA). They were selective elution using methanol or ethanol solution as solvent, and dynamic chromatographic separation using pyridyl resin with high selectivity. Results show that the chromatographic separation method can effectively enrich RA from stevia glycoside with high content of stevioside.

甜味剂莱鲍迪苷D的高效生物催化合成

采用来自水稻的UDP-糖基转移酶EUGT11并结合染色体改造构建了大肠杆菌工程菌,用于全细胞催化莱鲍迪苷A(Rebaudioside A,RA)生产莱鲍迪苷D(Rebaudioside D,RD)。为了增加宿主细胞内源性糖配体葡萄糖尿苷二磷酸(uridine diphosphate glucose,UDPG)的供给以满足糖基化反应需要,以大肠杆菌BL21(DE3)为出发菌对UDPG代谢通径进行改造,获得了一系列改造菌株SG1、SG2、SG3和SG4。其中以SG4为宿主过表达可高效催化RA合成RD的糖基转移酶EUGT11进行全细胞催化,RD产量高。随后以此工程菌为对象,对可能影响RD催化合成的条件进行了研究,结果表明50 m L培养菌液离心所收集新鲜菌体可在100 mmol/L pH 8.0磷酸钠缓冲液、80 mmol/L柠檬酸钠、体积分数0.1%Triton X100、500 g/L蔗糖、5 mmol/L Zn Cl2、42℃转化1 d的条件下催化1 mmol/L RA底物生成1112.21 mg/L RD,转化率可达98.5%。

TDZ-Induced High Frequency Plant Regeneration through Direct Shoot Organogenesis in <i>Stevia rebaudiana</i>Bertoni: An Important Medicinal Plant and a Natural Sweetener

An efficient high frequency plant regeneration protocol through direct organogenesis was developed for Sevia rebaudiana Bert. Nodal segments containing axillary buds were used as an explant and inoculated on Murashige and Skoog’s (MS) medium containing 3% (w/v) sucrose, 0.8% (w/v) agar supplemented with various concentrations of benzyladenine (BA), kinetin (Kn) and thidiazuron (TDZ) ranging from 1.00 to 9.00 μM. Maximum multiple shoots (96%) were obtained in MS medium supplemented with 1.0 μM TDZ with an average of 60 shoots per culture, having an average shoot length of 6.0 cm. The best in vitro root induction (89%) was achieved on half strength MS medium without any growth regulator with an average of 24 roots per culture and root length of7 cm. The rooted plantlets were successfully established in soil and grown to maturity at the survival rate of 95% in the indoor grow room. High-performance liquid chromatography was used to assess the stability in chemical profile and quantification of stevioside and rebaudioside A content of in vitro propagated S. rebaudiana plants and compared with their mother plant at the peak vegetative stage. Our results show no significant differences (p in vitro propagated plants. Furthermore, fully developed in vitro propagated S. rebaudiana plants were also compared with mother plant for their gas and water vapour exchange characteristics and leaf anatomy. The results show that in vitro propagated and hardened plants of S. rebaudiana are morphologically as well as functionally comparable to each other and to their mother plant.

Improvement of the Assay Method for Steviol Glycosides in the JECFA Specifications

Steviol glycosides are natural sweetener constituents found in the leaves of Stevia rebaudiana Bertoni (Asteraceae). The specifications for steviol glycosides were established by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) in 2008, although there was a call in the following year for the modification of this assay method to enable the determination of nine steviol glycosides rather than just seven. In response, based on a proposed method by the Japan Stevia Association, we developed an improved method by changing the HPLC conditions and including the use of an octadecylsilyl column instead of an amino-bonded column to enable the rapid and reliable determination of the nine steviol glycosides by an isocratic HPLC-UV method. With the developed method, the nine steviol glycosides can be separately determined, and identified using individual reference chemicals as standards, unlike the previous identification method, which was based on the relative retention times. In addition, the single stevioside quantification standard was replaced with both stevioside and rebaudioside A quantification standards. Importantly, the validation of the developed method was successful. The limits of quantification for the nine steviol glycosides were between 0.2% and 0.6%. The developed assay method for the nine steviol glycosides was proposed to JECFA and adopted as the revised assay method for the steviol glycosides specifications at its 73rd meeting in 2010.

THE SYNTHESIS AND CHARACTERIZATION OF SOME POROUS RESINS AND THEIR ADSORPTION PROPERTY ON STEVIA GLYCOSIDES

A series of porous resins (PYR) with different content of pyridyl group were prepared,and their physical structure and adsorption properties on the stevia glycosides werestudied in detail. Afler the selective adsorption of PYR resins, the rebaudioside A couldbe separated hem the other components of the stevia glycosides, and a new methodforobtaining pure rebaudioside A is reported.

Steviol Glycoside Content Dynamics during the Growth Cycle of Stevia rebaudiana Bert

The sweetener compounds in Stevia, steviol glycosides (SG), are mainly found in the leaves. The SG content depends on the plant’s growth stage and is usually highest just before flowering. In temperate areas, Stevia is a polyannual crop (5 - 7 years) with a vegetative period lasting from April-May until October, during which time the crop can be harvested two or three times. This research focuses on the need for knowledge about Stevia’s response to temperate climates in Southern Europe. Two field assays were established from June to October 2013 at two sites in Navarra (Spain). The biomass and content of the two major SG, stevioside (ST) and rebaudioside A (RA), were measured using High Performance Liquid Chromatography (HPLC) in 66 cloned plants, at different developmental stages. Although the results from the two sites showed different SG leaf content dynamics during the plant growth, the optimum harvest date at both sites coincided with the bud-flowering stage at the beginning of September (around 96 days after planting), when a ST yield of 27 g&middot;m-2 was reached. These results show Stevia’s potential as a commercial crop for stevioside production in northern Spain.

Selectivity of polymer adsorbent in adsorptive separations of stevia diterpene glycosides

Some hydrophobic (including both the non\|polar and polar) and hydrophilic polymer adsorbents were designed and synthesized, and their adsorption properties and adsorption mechanism toward stevia glycosides were studied in great detail. The skeleton structure and polarity of the resins had effect on the adsorption capacity and the selectivity properties during the adsorption of stevioside and rebaudioside A. A sweetener with high rebaudioside A content was isolated by using the adsorption selectivity of the polar resins.

Taste responsiveness to two steviol glycosides in three species of nonhuman primates

Primates have been found to differ widely in their taste perception and studies suggest that a coevolution between plant species bearing a certain taste substance and primate species feeding on these plants may contribute to such between-species differences. Considering that only platyrrhine primates, but not catarrhine or prosimian primates, share an evolutionary history with the neotrop- ical plant Stevia rebaudiana, we assessed whether members of these three primate taxa differ in their ability to perceive and/or in their sensitivity to its two quantitatively predominant sweet- tasting substances. We found that not only neotropical black-handed spider monkeys, but also paleotropical black-and-white ruffed lemurs and Western chimpanzees are clearly able to perceive stevioside and rebaudioside A. Using a two-bottle preference test of short duration, we found that Ateles geoffroyi preferred concentrations as low as 0.05 mM stevioside and 0.01 mM rebaudioside A over tap water. Taste preference thresholds of Pan troglodytes were similar to those of the spider monkeys, with 0.05 mM for stevioside and 0.03 mM for rebaudioside A, whereas Varecia variegata was slightly less sensitive with a threshold value of 0.1 mM for both substances. Thus, all three primate species are, similar to human subjects, clearly more sensitive to both steviol glycosides compared to sucrose. Only the spider monkeys displayed concentration-response curves with both stevioside and rebaudioside A which can best be described as an inverted U-shaped function sug- gesting that Ateles geoffroyi, similar to human subjects, may perceive a bitter side taste at higher concentrations of these substances. Taken together, the results of the present study do not support the notion that a co-evolution between plant and primate species may account for between-species differences in taste perception of steviol glycosides.