Separation of active components tyrosol and salidroside from Rhodiola rosea crude extract by two-step multistage fractionation extraction

https://doi.org/10.1016/j.cep.2022.108800Get rights and content

Highlights

  • Tyrosol and salidroside were selectively separated from Rhodiola rosea crude extract.

  • Three green organic solvent extraction systems were explored by solvent selection.

  • A two-step multistage extraction process was designed for multicomponent separation.

  • A mathematic model was established to simulate and optimize the extraction process.

Abstract

Rhodiola rosea contains many active ingredients, such as salidroside and tyrosol. However, separating the active components from Rhodiola rosea crude extract is difficult due to their similar physical properties. Multi-stage centrifugal fractionation extraction method was used due to its strong extraction and separation ability. Three solvents (n-butanol, n-amyl alcohol, and isobutyl acetate) with better distribution coefficient (k) and separation factor (α) were selected from nine organic solvents by single-stage extraction experiment. NaCl was used to break the two-phase emulsification during extraction. A two-step multi-stage extraction process was designed to separate multiple components. The multi-stage fractionation extraction experiments were carried out under the theoretical optimum conditions. In the first step, monomer 6 (tyrosol) was isolated and enriched in organic phase with a purity of over 94% using the above three solvents. In the second step using n-butanol as solvent, monomer 3 (picein) was enriched in organic phase with a purity of 93.6%, and monomer 5 (salidroside) was enriched in aqueous phase with a purity of 85.2%. Finally, the effect of the number of stages was simulated for the separation of picein. The yield of picein reached 80%, and the purity was close to 100% by more than 20 stages.

Introduction

Rhodiola is a herbaceous or sub-shrub plant with strong environmental adaptability and vitality. There are more than 90 kinds of Rhodiola around the world, which are mainly distributed in northwest Asia, North America, and the Himalayas. Rhodiola has a long history of application. More than 2000 years ago, people on the Tibetan Plateau used it as medicine to strengthen their bodies and resist the influence of bad environment [1], [2], [3], [4], [5], [6]. Modern pharmacological studies showed that Rhodiola has many functions such as anti-anxiety [2], anti-aging [3], anti-depressant [4], immune regulation [5], and hepatoprotection [6]. Many types of Rhodiola commercial medicinal materials are available, which have different qualities because of the differences in medicinal ingredients and content. Moreover, some varieties contain toxic ingredients. Therefore, the precise separation of the active ingredients from Rhodiola rosea crude extract is particularly important.

The chemical composition of Rhodiola plants has been studied extensively. In general, Rhodiola contains a variety of chemical components, including coumarins, flavonoids, glycosides, alkaloids, inorganic elements, amino acids, cellulose, starches, and vitamins [1]. At present, more than 40 chemical components have been separated from various Rhodiola plants. Among them, the main pharmacologically active ingredients are salidroside and its aglycone tyrosol [7,8]. These active ingredients are the target extracts of this work. However, separating these active ingredients is very difficult due to their similar physicochemical properties.

Salidroside is a characteristic component of Rhodiola plants and also the main active component. It is nontoxic and harmless to the human body and conforms to the life philosophy of modern people, which is applied to daily chemical products such as cosmetics and detergents. As a kind of multi-saponin, it is mainly derived from the dry roots and rhizomes of Rhodiola crassulata, with a molecular formula of C14H20O7 and a molecular weight of 300 as shown in Fig. 1 [9]. It is soluble in water, ethanol, and n-butanol, while slightly soluble in acetone and ether. Salidroside can be completely hydrolyzed under acidic conditions by heated reflux in a water bath for 2 h. The hydrolyzed product is one molecule of glucose and one molecule of aglycone tyrosol. Therefore, distillation and other thermodynamic methods are not suitable to separate salidroside from the perspective of stability.

Currently, three methods can be used to obtain salidroside: extraction and purification from plants, synthesizing through chemical method, and synthesizing by biotransformation or biocatalysis [10], [11], [12], [13], [14]. Among them, the existing methods for the separation and purification of salidroside from plants include column chromatography [10,11], supercritical carbon dioxide extraction [12], and aqueous two-phase extraction [13]. Column chromatography usually refers to the purification of salidroside using macroporous adsorption resin column, high-speed countercurrent chromatography, or preparative high-performance liquid phase chromatography (HPLC). However, none of these chromatography methods can satisfy high purity and mass production at the same time. Supercritical carbon dioxide extraction can obtain high-purity salidroside, while the separation process requires high demands for equipment. Although aqueous two-phase extraction has high recovery rate and low energy consumption, it is not suitable for mass production yet due to the instability. As for the chemical synthesis of salidroside, various synthetic routes have certain disadvantages, such as time-consuming, poor selectivity, or low yield. Moreover, many chemical reagents are used in these synthesis processes, which may be highly toxic and unfriendly to the environment. The biosynthesis of salidroside has some limitations. For example, it is susceptible to cell growth and environmental factors in the process of cell culture. Enzyme catalysis for synthesizing salidroside is usually mild and has high stereoselectivity, but the most commonly used enzyme of free β-glucosidase has poor stability, especially in some organic solvent medium reaction systems with strong hydrophilicity, which may cause low catalytic activity and yield [14].

Tyrosol is also one of the effective ingredients of Rhodiola. In the pharmacological research of Rhodiola, the pharmacological effects of tyrosol, including anti-hypoxia and anti-fatigue, are similar to those of salidroside [15]. Tyrosol is a β-hydroxyphenethyl alcohol with a molecular formula of C8H10O2 and a molecular weight of 138 as shown in Fig. 2. It is soluble in polar solvents such as water, ethanol, ether, acetone, and acetic acid.

Tyrosol is an important intermediate of medicines and spices. It can be used to synthesize many drugs, such as metoprolol, betarolol, and maltine. According to the reports [16], tyrosol can be used in health foods for the prevention and treatment of Alzheimer's disease and in the preparation of medicines for the treatment of diabetic complications. Tyrosol composition is composed of tyrosol and hyaluronic acid, lutein, procyanidins, taurine in a certain proportion, which has the effects of improving eyesight, improving eyes and visual functions to protect eyesight, improving visual fatigue, and adjuvant treatment of macular degeneration, macular degeneration, diabetic retinopathy, optic nerve atrophy, degeneration, etc. However, the research on the extraction of tyrosol from plants is still in its infancy. The synthetic methods of tyrosol generally have shortcomings such as long route, high cost, and low yield, which limit its industrial production scale [17].

The main method for the separation and purification of Rhodiola rosea crude extract is column chromatography [18], including silica gel columns and ion exchange resin columns. These techniques cannot be used to separate tyrosol from phenols in large-scale. Liquid-liquid extraction is suitable for continuous separation and purification of Rhodiola rosea crude extract, and the extraction solvent is easy to recycle than the multicomponent chromatography mobile phase. Centrifugal extraction is an intensified extraction technique to realize liquid–liquid phase mixing and phase separation by means of centrifugal force field [19], [20], [21], [22], [23], [24]. Compared with other extraction technologies, it has short contact time of two phases, fast phase separation speed, and wide operating range. This technology has also been successfully applied in many fields such as petrochemical engineering [25,26], rare earth element separation [27,28], chiral separation [29], and hydrometallurgy [30]. Several research works on multi-stage centrifugal extraction have been carried out [31], [32], [33], [34], [35], [36]. In addition, recent studies revealed that this method is very effective for the separation of natural products [37], [38], [39], [40]. In this study, centrifugal fractionation extraction technology was used to separate the active components of Rhodiola rosea crude extract. Multiple solvent systems were investigated. This method has the potential to effectively separate the active components of Rhodiola rosea with high yield and purity simultaneously. The multistage fractionation process is shown in Fig. 3.

Section snippets

Materials

Rhodiola rosea crude extract was purchased from Nanjing Yuanzhi Biotechnology Co. LTD. The crude extract was obtained by water leaching. The purchased yellow solid powder was used, and the powder was dissolved in water to obtain a liquid phase aqueous solution. The chromatographic solvents are HPLC grade. The main reagents used in this work were listed in Table 1.

Analytical method

The concentration of different monomers in Rhodiola rosea crude extract was determined by HPLC with the injection volume of 20 μL [39]

Theory and modeling

Distribution coefficient (k) and separation factor (α) were used to evaluate the separation ability of the active components of Rhodiola rosea crude [42]. In the extraction process of Rhodiola rosea crude extract, each monomer was distributed in two phases in the form of molecule, which belongs to physical distribution without the addition of extractant. For each unit (j = 1, …, N), the parameters (k and α) are used to evaluate the efficiency.ki,j=Ci,org,jCi,aq,jwhere i is each monomer of

Results and discussion

An effective route was used to isolate the active component of Rhodiola rosea crude extract (Fig. 7). Firstly, the k values of monomers in different organic phases were obtained by single extraction experiments with different organic solvents. Secondly, in the same organic solvent, the k of all monomers was sorted, and the α of the target substance was calculated. Finally, an organic solvent with appropriate partition coefficient and large separation factor was selected, and the optimal process

Conclusion

To separate the medicinal active components of Rhodiola rosea crude extract, three organic solvent systems (n-butanol, n-amyl alcohol, and isobutyl acetate) were selected by single-stage extraction experiments. A two-step multi-stage extraction process was designed and verified to efficiently separate tyrosol, picein, and salidroside.

  • (1)

    In the single-stage extraction experiments, nine solvents were explored. By selecting appropriate k value and larger α value, three solvent extraction systems were

CRediT authorship contribution statement

Xiaohui Feng: Data curation, Writing – original draft, Investigation, Methodology, Visualization, Software, Validation. Wanru Wang: Validation. Fusong Liu: Software. Panliang Zhang: Supervision. Fengci Tang: Investigation. Lelin Zeng: Writing – review & editing, Supervision. Kewen Tang: Conceptualization, Methodology, Supervision, Data curation, Funding acquisition, Project administration.

Declaration of Competing Interest

The authors declare no conflict of interest.

Acknowledgments

This work was supported by the Innovation Research Group Project of Natural Science Foundation of Hunan Province (No. 2020JJ1004), the National Natural Science Foundation of China (No. 22178092), the Key Research and Development Project of Hunan Province (No. 2020NK2037), the Scientific Research Fund of Hunan Provincial Education Department (No. 20A227), and the Hunan Provincial Innovation Foundation for Postgraduate (No. CX20201113).

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