Extraction and chemical structure of polysaccharides from Rehmannia Rehmannia

Rehmannia glutinosa Libosch is a plant in the Scrophulariaceae family. Fresh or dried root tubers. Clinical medicine is generally divided into three categories, one is picked and cleaned directly into medicine, called fresh Rehmannia, the effect of clearing heat and promoting fluid, cooling blood, hemostasis; One is to slowly bake it to about 80% dry, called raw Rehmannia, the effect is to clear heat and cool blood, nourishing Yin and Shengjin; One is according to the stewed method of wine, steamed processing, called cooked Rehmannia, the effect of tonifying blood and nourishing Yin, supplementing essence and filling marrow. Rehmannia mainly grows in Liaoning, Hebei, Henan, Shandong and other places, and is cultivated all over China and abroad. Studies have found that Rehmannia has pharmacological activities such as blood tonic, anti-aging, anti-tumor, antibacterial, hypoglycemic, immunomodulatory, neuromodulatory, etc. It is widely used in traditional Chinese medicine and modern drug active ingredient development. Rehmannia Rehmannia contains terpenoids, flavonoids, polysaccharides and other chemical components, and more than 200 compounds have been isolated and identified. Rehmannia polysaccharide is one of the important bioactive components of Rehmannia. It has significant effects on anti-inflammatory, antioxidant, diabetes, neuromodulation, etc., and no significant toxicity studies have been reported. With the development of research, more and more attention has been paid to Rehmannia polysaccharides, from extraction methods to structural properties and drug administration applications. Natural polysaccharide has the advantages of soluble in water, non-toxic, non-immunogenicity and easy modification. It is easier to exert its curative effect when polysaccharide is combined with carrier or modified. In addition to its many pharmacological effects, Rehmannia polysaccharide can also be combined with liposome, nano and other new drug delivery technologies to expand its efficacy.

Extraction of polysaccharides from Rehmannia

The extraction of polysaccharides is the premise of studying the properties of polysaccharides. Rehmannium polysaccharide is a kind of complex structure system composed of multiple monosaccharides, which has different physical properties and chemical activities. Therefore, the selection of Rehmannia polysaccharide extraction method should consider its chemical properties, extraction conditions and the influence of interfering substances to ensure that the maximum extraction rate is achieved without affecting the structure and chemical properties. At present, the commonly used extraction methods of Rehmannia polysaccharides include water extraction and alcohol precipitation, organic solvent extraction, ultrasonic extraction, CO2 extraction and enzymatic hydrolysis.

The traditional method of water extraction and alcohol precipitation is a common extraction process of polysaccharides, which is simple to operate and widely used. Zhao Pingge et al. extracted Rehmannia polysaccharide with 10 times the amount of hot water and 95% ethanol precipitation, the crude polysaccharide accounted for 45.5% of the total sugar content, the extraction rate was 16.02%, and the effect was good. Under the optimal extraction technology of water extraction and alcohol precipitation, the extraction yield of Rehmannia polysaccharides was 7.09%. The yield of polysaccharide extracted by water extraction and alcohol precipitation is low, which belongs to crude product and needs further purification. Sun Yuechuan et al. used 60% methanol as extraction solvent and single factor orthogonal experiment to obtain the optimal reflux extraction process of Rehmannia polysaccharides as solid-liquid ratio of 1∶8, extraction time of 1.5h, extraction temperature of 90℃, and polysaccharide yield of 66.32% of total sugar content. Using ethanol as extraction solvent, Xu Haiyan et al. adopted response surface method to optimize the extraction process as follows: when ethanol concentration is 30%, ultrasonic time is 16min, and solid-liquid ratio is 1∶10, the polysaccharide yield is 16.15%.

In recent years, supercritical CO2 extraction, microwave extraction, ultrasonic extraction and enzymolysis extraction have been widely used. Liu Hua et al. optimized the process of supercritical CO2 extraction, and the yield of polysaccharide was 30.4%. Kong Yuanfang et al. optimized the process of extracting polysaccharides from Rehmannia Rehmannia by microwave extraction, that is, microwave extraction for 150 s, solid-liquid ratio of 1∶10, and temperature 80 ℃, the polysaccharide yield was 72.10% of the total sugar content, and the yield was high. Ultrasonic extraction method can increase the permeability of cell wall and cell membrane, and is more conducive to the dissolution of polysaccharide components, saving time and simple operation. Tian Chunlian et al. obtained the optimal extraction process of polysaccharide from Rehmannia Rehmannia by ultrasonic extraction with orthogonal test. Under ultrasonic time of 30min, solid-liquid ratio of 1:40 and temperature of 40 ℃, the polysaccharide yield of roots, stems and leaves of Rehmannia Rehmannia was 15.74%, 8.36% and 4.21%, respectively, and the content in different parts had great differences. Enzyme method is a green and efficient extraction technology, enzymes can destroy the cell structure, so that the substance dissolves, and the action condition is mild, will not damage the biological activity of polysaccharide. Li Wenbo enzymolized rehmannium with cellulase and optimized the effects of extraction temperature, extraction time, pH value of extraction solution and solid-liquid ratio on polysaccharide yield. The yield of this method was as high as 21.4%, which is a new, efficient and mild extraction method.

Structural modification of Rehmannia polysaccharides

The synthesis of polysaccharide derivatives is a new method to change the properties of polysaccharides, increase the stability and improve the curative effect. Depending on some chemical methods, such as changing the hydroxyl group, carboxyl group, amino group and other chemical groups on the sugar residue, it is possible to improve the activity of polysaccharide. Dai Guonna et al. combined rehmannia polysaccharide with selenium with acetic acid as catalyst to produce a rehmannia selenium polysaccharide, which can obviously promote the phagocytosis ability of mouse macrophages, promote the proliferation of mouse spleen lymphocytes, and promote the Th1 cytokine interleukin-4 (IL-2) and interferon-γ. The experiment showed that selenium polysaccharide of Rehmannia can significantly enhance the immunity of mice. The acetylation of polysaccharides can significantly improve the activity of polysaccharides. Yang Ying et al. optimized the acetylation process of Rehmannium polysaccharide. Under the condition that the ratio of acetic anhydride to Rehmannium polysaccharide was 2.7 and the reaction temperature was 48℃ for 3.0h, the degree of acetyl substitution of Rehmannium polysaccharide was 0.327. The results showed that the antioxidant capacity of acetylated Rehmannia polysaccharide was significantly improved compared with unacetylated Rehmannia polysaccharide.

Chemical structure of Rehmannia polysaccharides

Polysaccharide is a kind of macromolecular compound which is connected by monosaccharide through glucoside bond. Its structural characteristics are usually defined by relative molecular weight, monosaccharide composition, chain conformation, branch structure, etc. Different extraction methods will result in different structure of polysaccharide and affect its pharmacological activity, so it is very important to study its structural characteristics to modify its structural composition and explore its pharmacological activity. The analytical methods used to identify the structure of polysaccharides include high performance liquid chromatography, gas chromatography-mass spectrometry and infrared spectroscopy.