Astragalus radix was the dried root of Astragalus membranaceus of leguminous plant, is one of the most commonly used medicinal herbs originating from eastern and northern China, Mongolia, and Korea. It has been used for centuries for increases immunity and prevents spleen deficiency. Its primary active extract is polysaccharides, flavonoids, and saponins. The medicinal benefits of Astragalus are well documented, with its main medicinal component being the Astragalus polysaccharide. Its bioactive components promote immune responses and produce antibodies. It also has several antiviral, antitumor, and anti-inflammatory properties. These compounds are potent antioxidants, antitumor agents, and cardiovascular and liver-protective properties. Astragalus polysaccharide are now used as an immune enhancers and antiviral drugs are widely used in medicine and livestock exposure. Now the extraction methods of Astragalus polysaccharide include: Water extraction, Alkali alcohol extraction, Microwave-assisted extraction, Ultrasonic extraction, Ultra-high pressure extraction method and other new technique, this paper lists the commonly used extraction methods of APS:

Water extraction

Astragalus polysaccharide (APS) is a water-soluble component in Astragalus membranaceus and is usually extracted by water extraction. The commonly used methods are: water decocting method, water extraction, water reflux extraction and alkali water extraction. As an Astragalus polysaccharide factory, Rainbow Biotech mainly uses alcohol/water extraction method.

It was found that chemical or biological treatment of astragalus membranaceus could significantly improve the yield of polysaccharides. The chemical treatment is mainly degreasing with an organic solvent to reduce the content of impurities in the extract. Considering the toxicity and maneuverability of degreasing solvent, high concentration ethanol degreasing is mostly used. The experimental process is as follows: Astragalus membranaceus was defatted by 3 times of 95% ethanol for 1. 5 h, then extracted with 8 times of water for 90 min at 100 ℃ for 3 times. The extraction yield of crude polysaccharide and the yield of polysaccharides in terms of glucose was 14.76% and 4.78% respectively. The alcohol dewatering method has been deeply integrated into most APS extraction methods, that is, most of them use high concentration ethanol solution (80% ~ 95%) to remove some impurities before extraction, in order to facilitate the subsequent separation and purification of polysaccharides and other processing, to obtain higher purity.

APS with different molecular weights could be obtained by direct or fractional alcohol precipitation of water extract after concentration. After water extraction and alcohol precipitation, APS purification process often needs to be deproteinized, commonly used methods are enzyme method, Sevage method, trichloroacetic acid method, of which enzyme method and Sevage method can achieve the best results. After protein removal, astragalus polysaccharide was obtained by dialysis and freeze-drying. Astragalus polysaccharides can be further prepared by chromatography column with different packing types, including ion-exchange chromatography column, commonly used diethylaminoethyl fibrin (DEAE series), gel exclusion chromatography column (Sephadex-G series, Superdex series, etc.). Astragalus polysaccharides with different properties and molecular weights can be separated by a proper chromatography column.

Alkali alcohol extract
The alkali-alcohol extraction was improved on the basis of the alkali-water extraction of APS. Alkali solution can obviously break the wall of plant cells, swell and dissolve plant fibers, while alcohol solution has strong permeability. Under the combined action of alcohol and alkali, the permeability of APS was increased and the residual amount of POLYSACCHARIDES in plant tissues was reduced, so as to improve the extraction rate.

The results showed that the optimal extraction conditions of ASTRagalus polysaccharides were as follows: solid-liquid ratio 1 ∶ 10, pH value 12 5% Na2CO3 ethanol solution, 90 ℃ extraction for 90 min, the extraction yield of polysaccharides was 19.15%, and the content of active components in the residue was low. The extraction rates of water and alcohol extraction, alkali water extraction and alkali alcohol extraction were 3.62%, 7.64% and 9.74% respectively. The extraction technology was NaOH alcohol solution with a pH value of 12, the ratio of solid to liquid was 1∶ 10, and the extraction time was 3 h, 2.5 h, and 2 h, respectively. Compared with the traditional extraction methods, the extraction rate of ASTRagalus polysaccharides by this method is higher, and the product purity and stability are better, but the production equipment has higher requirements.

Microwave-assisted extraction

Microwave extraction of Astragalus polysaccharide is a highly effective extraction method, also known as microwave-assisted extraction, is an extraction method combining traditional solvent extraction with microwave, which takes advantage of microwave’s strong penetration, short extraction time and high heating efficiency. The microwave technique creates a volumetric heat source that penetrates materials. The microwave energy induces molecular friction by dipolar rotation of polar solvents and conductive migration of dissolved ions. The rapid thermal effect of microwave can break cell wall and inactivate the enzyme in cell membrane, so that the polysaccharide components in cells can be extracted more easily, and the extraction rate of ASTRagalus polysaccharide is greatly increased.

The astragalus polysaccharides were prepared by organic solvent degreasing, adjusting machine power and water reflux extraction in a continuous microwave reactor. The extraction time of astragalus polysaccharides was shortened and the solvent consumption was increased. The extraction rate of astragalus polysaccharides was (4.502%-6.55%).

The new technique reduced the need for extraction solvent, decreased the amount of time required to extract the drug, and is environment-friendly. Moreover, it did not require any special laboratory setup. This technology was also cost-effective, as the microwavable material is cheaper than conventional methods.

Ultrasonic extraction
This is a new polysaccharide extraction technology. Ultrasonic accelerated the swelling and hydration process of astragalus membranaceus, which was conducive to the faster transfer of polysaccharides to the extraction solvent through osmosis and diffusion. In addition, ultrasonic cavitation can destroy the structure of cell wall and cell membrane, and accelerate the dissolution of intracellular polysaccharide. The optimal conditions of ultrasonic extraction were determined by orthogonal test as follows: ultrasonic power 300 W, temperature 50 ℃, solid-liquid ratio 1∶ 30, extraction for 4 times. When the extraction time was 40 min, the extraction power was 1 000 W, and the ultrasonic time/gap time ratio was 1∶ 1, the extraction yield of polysaccharide reached 11.44%.

Ultra-high pressure extraction method
Ultra-high pressure extraction technology is a new extraction technology for the active components of natural products. It means that the hydrostatic pressure of 100 ~ 1 000 MPa is applied to the material liquid at normal temperature, and the pressure is relieved quickly after holding the pressure for a period of time, so that the osmotic pressure difference between internal and external cells suddenly increases, and various membranes of cells are destroyed and then go for the extraction. In addition, because the ultrahigh pressure extraction is carried out at room temperature, the problem of the decrease of biological activity caused by thermal effect can be effectively avoided during the extraction of APS. Astragalus polysaccharide was extracted by ultra-high pressure technology under the following conditions: pressure 350 MPa, solid-liquid ratio 1∶ 60, soaking time 5 h, holding time 2 min, and the extraction yield was 24.28%.

In the past, scientists used conventional methods to extract Astragalus polysaccharide. At present, limited by equipment, cost and process, water extraction is still the most widely used method because of its low cost, safety and other characteristics. These methods often produced inferior results due to the complex nature of the plant. In this study, some new extraction technology was developed to improve the quality of astragalus polysaccharide, which provided new insights about the mechanism of mass transfer in Astragalus polysaccharides.