Purification and Preparation of Rebaudioside A from Steviol Glycosides Using One-Dimensional Hydrophilic Interaction Chromatography

Validation of UHPLC-ESI-MS/MS Method for Determining Steviol Glycoside and Its Derivatives in Foods and Beverages

The aim of this study was to validate a method for determining nine types of steviol glycoside and its derivatives in food and beverage products, using ultrahigh-performance liquid chromatography tandem mass spectrometry with electrospray ionization (UHPLC ESI MS/MS). The performance characteristics of the analysis method were determined along with their suitability for the intended use. Coefficient of determination (R2) calibration curves from 0.2 to 1.0 mg L-1 were in the ranges of 0.9911-0.9990, 0.9939-1.0000 and 0.9973-0.9999 for a beverage, yogurt and snack, respectively. Intra-day precisions in terms of percent relative standard deviation (% RSD) of concentration, at 0.2, 0.5 and 1.0 mg L-1, for the beverage, yogurt and snack were lower than 15% (1.1-9.3%). At all concentrations, percentage recoveries were in the accepted range of 70-120%. For the matrix effect study, matrix-matched calibration was used for all compounds, obtaining a linear concentration range from 0.2 mg L-1 to 1.0 mg L-1. Almost all matrix-matched results presented as percentage recoveries were within the accepted range of 80-120%. The limit of detection (LOD) for steviol glycosides ranged from 0.003 to 0.078 μg g-1, while the limit of quantitation (LOQ) ranged from 0.011 to 0.261 μg g-1. These results indicate that the modified test method can be applied to determine the presence of steviol glycoside and its derivatives in a wide range of sample matrices.

Validation of an HPLC Method for Pretreatment of Steviol Glycosides in Fermented Milk

Steviol glycosides are used in food and beverages worldwide as natural sweeteners, serving as a low-calorie sugar substitute. The acceptable daily intake of steviol is 0-4 mg/kg body weight. The rising demand for dairy products has led to a corresponding increase in the use of steviol glycosides in such products. Therefore, it is important to analyze the levels of steviol glycosides in dairy products. Dairy products have high fat contents and unique emulsion characteristics, conferred by a mixture of fat globules, casein micelles, whey proteins, and numerous other small molecules. These characteristics may interfere with the estimation of steviol glycoside levels; therefore, dairy samples require pretreatment. We aimed to develop an objective test for measuring the levels of steviol glycosides through the development of an efficient pretreatment method. In this study, the steviol glycoside content in dairy products was evaluated by using various methods, and an optimal pretreatment method was determined. We used high-performance liquid chromatography to assess the selectivity, linearity, limit of detection, limit of quantification, accuracy, precision, and recovery rate. Calibration curves were linear in the range of 1-50 mg/kg, with a coefficient of determination of ≥0.999. The limit of detection and limit of quantification were in the ranges of 0.11-0.56 and 0.33-1.69 mg/kg, respectively. The relative standard deviation (%) represents the precision of a measurement. The RSD relative standard deviationof recovery varied between 0.16% and 2.83%, and recovery of the analysis varied between 83.57% and 104.84%. These results demonstrate the reliability of the method for measuring the steviol glycoside content. This method can be used for the simple pretreatment of steviol glycosides and can provide an accurate determination of steviol glycoside content in emulsified food matrices, such as dairy products.

A ternary eluent strategy to tune the peak shape of steviol glycosides in reversed-phase liquid chromatography

In this paper, an effective strategy of using acetonitrile-methanol-water as mobile phase was developed to achieve acceptable peak shape of steviol glycosides in reversed-phase liquid chromatography (RPLC). The change of elution profiles of rebaudioside A (RA) was systematically investigated. Two classical distributions, namely, tailing and fronting peaks resulting from injections of RA solution in range of 0.5-5 mg were both observed in a ternary eluent of acetonitrile-methanol-water (21:43:36, v/v). Next, a three-phase diagram of tailing factor (Tf) was illustrated, showing high dependence of elution profile of RA on the ternary composition. The peak shape of RA can be adjusted mainly based on the additive effect, that is, acetonitrile is more strongly adsorbed to the stationary phase than RA in the pure weak solvent (H2O). Therefore, with the increase of acetonitrile concentration in the ternary eluent, the RA band profiles went from being tailing to fronting shapes. At the same time, due to the large RA-RA interactions, there was anti-Langmuir adsorption isotherm in acetonitrile-water mobile phase, which is the reason for the fronting peaks of RA. It could be concluded that the way of using the ternary eluent of acetonitrile-methanol-water does control and tune the peak shape of steviol glycosides in RPLC separation.

Kinetics and thermodynamics of rebaudioside A adsorption on a strongly acidic cation exchange resin

To explain the mechanism underlying the adsorption of stevia's polar component rebaudioside A in hydrophilic interaction liquid chromatography mode, the characteristics of rebaudioside A adsorption on various resins in an organic-solvent-rich system were studied. Among the tested resins, the strongly acidic cation resin FPC11 showed the best adsorption behavior for rebaudioside A. The factors affecting the adsorption kinetics of the resin for rebaudioside A are discussed. The results showed that the pseudo-second-order reaction model and intra-particle diffusion model best described the adsorption kinetics of rebaudioside A on the resin. The adsorption rate was controlled by physical sorption, mainly via electron sharing or electron transfer between the adsorbent and the adsorbate. The adsorption process with multiple stages involved weak initial adsorption behavior. Thermodynamic studies showed that the adsorption of rebaudioside A on the resin was not an ideal monolayer adsorption, but mutual adsorption effects between the adsorbates. The adsorption was a spontaneous, entropy-increasing endothermic process. The synergistic effect of hydrogen bonding and ion-dipole was a possible driving force.

Retention of stevioside polar compounds on a sulfonic acid-functionalized stationary phase

To explore the retention and separation of stevioside polar compounds on a sulfonic acid-functionalized cation exchange column, the effects of different organic solvent-water mobile phases on the retention behavior of polar rebaudioside A (RA) and its analogues on the column were investigated over a wide range of organic solvent contents. The obtained U-shape curves hinted that the retention of the compounds on the same column transitioned from a reversed-phase liquid chromatography (RPLC) mode to a hydrophilic interaction liquid chromatography (HILIC) mode when the water-rich state in the mobile phases changed to an organic solvent-rich state. Under the RPLC mode, no separation of RA from its analogues was observed. The HILIC mode was beneficial to the retention and separation of RA and its analogues. Compared with polar protic solvents, aprotic solvents were more conducive to the retention and separation of the polar compounds based on the HILIC mode in organic solvent-rich mobile phases. Three models were used to evaluate and discuss the HILIC retention and separation of the compounds on the column. In the aprotic solvent-rich mobile phase, the HILIC retention of RA and its analogues was effectively described by a mixed-mode model; in the polar proton solvent-rich mobile phase, the retention of analytes was best described by an linear solvation strength (LSS) model. The content and composition of the organic solvent in the mobile phase were determined to be important influencing factors that regulated the retention time for the RA and its analogues, and even the separation mechanism for HILIC. The present work provides a theoretical basis for guiding one to prepare high-purity RA from its analogues by predicting the retention time.