How to Extract Astragalus Polysaccharides from Astragalus Membranaceus Root?

Astragalus, first mentioned in the Divine Husbandman's Classic of the Materia Medica under the name “Huangqi”, has a medicinal history of more than 2,000 years and enjoys the reputation of being “the best Qi tonic”. It is a dual-use species of medicine and food announced by the National Health Commission. Astragalus polysaccharide is one of the main active ingredients of astragalus. It has various physiological functions such as improving immunity, antibacterial, anticancer, protecting the intestines, anti-aging, antiviral, and protecting the cardiovascular system[1-2]. It is also a natural medicine for the treatment of metabolic dysfunction-related fatty liver disease[3], and has become a hotspot of research in recent years. This paper reviews the literature on the extraction methods of astragalus polysaccharides and their application in health drinks, with the aim of providing guidance for the large-scale industrial production of astragalus polysaccharides and providing a reference for the development and utilization of astragalus polysaccharides and related products.

1 Extraction methods

The development and utilization of astragalus is closely related to the extraction efficiency of astragalus polysaccharides in its tissues. In order to improve the extraction efficiency of astragalus polysaccharides, scholars have conducted a large number of studies on the extraction methods of astragalus polysaccharides. There are many methods for extracting astragalus polysaccharides. Commonly used traditional extraction methods include the water extraction and alcohol precipitation method, the alkali extraction and alcohol precipitation method, etc. In recent years, modern extraction methods such as ultrasonic-assisted extraction, microwave-assisted extraction, and enzymatic extraction have also been widely used, and experiments have confirmed that they have a high extraction effect.

1.1 Water-alcohol precipitation

The traditional water-alcohol precipitation method uses hot water to extract or boil the material to obtain an extract, which is then concentrated and precipitated to obtain an extract. This method is inexpensive and safe, and is currently the most commonly used method [4]. However, it consumes a lot of solvent, the purity of the polysaccharides is relatively low, and the difficulty of separation and purification increases. In order to improve the yield of polysaccharides, many researchers have carried out research on the extraction process. Wen Xiyan et al. [5] used the yield of dry extract and the polysaccharide content as evaluation indicators to explore the effects of the liquid-to-material ratio, extraction time and number of extractions on the efficiency of polysaccharide extraction.

The results showed that the number of extractions and time had a significant effect on the efficiency of polysaccharide extraction, while the liquid-to-material ratio was not statistically significant. The results of the orthogonal test showed that the highest yield of extract was obtained when the liquid-to-material ratio was 1:8, the extraction was carried out three times, and each extraction lasted 1.5 h. Qiao Lijie et al. [6] used Tianshan Astragalus as the research object and determined the polysaccharide extraction process through comprehensive analysis of response surface and single factor: a liquid-to-material ratio of 1:32 and extraction at 92 °C for 3 h. Practical verification has shown that the polysaccharide content obtained using this process is close to the predicted value.

1.2 Alkali extraction and alcohol precipitation

Compared with water extraction and alcohol precipitation, it has the obvious advantages of high purity and stability of the product, but it has high requirements for equipment in practical applications, and the wastewater generated during the extraction process needs to be treated before it can be discharged.

Jin Fenfen et al. [7] investigated the effect of different extraction methods on the extraction rate of astragalus polysaccharides. The results showed that the polysaccharide extraction rate was 9.74% when extracted with an alcohol solution with a concentration of 5% and a pH of 12, while the polysaccharide extraction rate was 7.64% when extracted with alkali water alone. It can be seen that the alkali-alcohol extraction method is superior to the alkali water extraction method. Xie Dandan et al. [8] used a 1% KOH solution to extract astragalus polysaccharides, comparing the effects of different extraction temperatures, extraction times and material-to-liquid ratios on the polysaccharide extraction rate. The results showed that the optimal process for the alkaline extraction and alcohol precipitation method was a material-to-liquid ratio of 1:20, and the extraction was carried out at 70 °C for 130 minutes.

1.3 Ultrasonic-assisted extraction technology

This method uses the cavitation effect of ultrasound to allow the extraction solvent to enter the cells, speeding up the release and dissolution of the active ingredients. The method is simple to operate, and the main process parameters are extraction temperature, extraction time, solid-liquid ratio, and ultrasonic power. Chen Shouni [9] used Astragalus membranaceus processed pieces as the raw material and, by optimizing the extraction process, achieved a polysaccharide yield of 5.862%. Wei Zengyun[10], Wang Dan[11], Li Lihong[12] and other researchers used the orthogonal array method and response surface method to optimize the extraction process.

Yu Ping[13] compared these two optimization methods. The research shows that compared with the orthogonal array method, the optimization model established by the response surface method can better predict the extraction rate at different factor levels, and the accuracy is slightly higher. Therefore, the response surface method was applied to the process optimization of extracting astragaloside IV in order to screen the optimal process conditions. This paper reviews the literature from the China National Knowledge Infrastructure and summarizes the extraction processes of various researchers as follows, as shown in Table 1. A large number of studies have shown that ultrasonic-assisted extraction technology is easy to control. Compared with traditional extraction methods, it is fast, low-temperature, energy-saving and environmentally friendly, and can be used in the industrial production of astragaloside IV.

1.4 Microwave-assisted extraction method

This method uses the thermal effect of microwaves to cause cracks or pores in the plant cell wall, facilitating the dissolution of intracellular substances. It has the advantages of being easy to operate, fast, low cost, high efficiency, few by-products, and easy extraction, but there is a possibility that it may affect the structure and physiological activity of polysaccharides. In recent years, it has been widely used in the field of extracting the active ingredients of traditional Chinese medicine.

Factors affecting this method mainly include microwave power and extraction time. Prolonging the extraction time can increase the reflection and absorption of microwaves, enhance the penetrating effect of microwaves on astragalus, and improve the extraction rate of polysaccharides [15]. Liang Taishuai et al. [16] studied the extraction conditions of astragalus polysaccharides from Astragalus membranaceus by orthogonal design. The results showed that the highest polysaccharide yield was 7.97% with a liquid-to-solid ratio of 20:1, microwave extraction for 10 minutes at a power of 450 W, and a total of 3 extractions. Zhao Fengchun et al. [17] studied the optimal process conditions to be an extraction time of 10 min, a microwave power of 360 W, and a liquid-to-solid ratio of 5:1, with a polysaccharide yield of 3.28%. Compared with direct heating extraction, the extraction time can be significantly shortened, but the purity is low.

1.5 Enzyme hydrolysis

This method uses enzymes such as cellulase and pectinase to break down the cell walls and promote the release of intracellular polysaccharides. Long Liangkun et al. [18] selected cellulase to hydrolyze the Astragalus membranaceus residue, and used single factor experiments and orthogonal experiments to explore the effects of enzyme dosage, temperature and time on polysaccharide extraction and to optimize the extraction process. The results showed that : When the amount of cellulase enzyme used is 4 U/g and the enzyme is hydrolyzed at 45 °C for 4 h, 44.6 mg/g polysaccharides can be obtained, which is 41.7 mg/g higher than the control group. It is clear that the use of cellulase to enzymolyze astragalus can greatly increase the amount of polysaccharide extracted. Dong Lingling et al. [19] used the extraction rate and mass fraction of astragalus polysaccharide as the indicators for investigation, and used the cellulase enzymolysis-microwave extraction method to extract astragalus polysaccharide, and compared the effects of different extraction methods.

The results showed that: at an enzyme-to-material ratio of 57.6 U/g, a liquid-to-solid ratio of 10:1, and an enzymatic hydrolysis time of 60 min, the highest polysaccharide extraction rate of 16.07% was achieved using microwave power of 480 W, and the polysaccharide mass fraction was 88.40%. The extraction rates of the direct enzymatic method, microwave extraction method, and water reflux extraction method were 10.64%, 13.74%, and 4.82%, respectively, and the mass fractions of the three were 63.86%, 66.00%, and 37.54%, respectively. It can be seen that the enzymatic hydrolysis-microwave extraction method has the highest polysaccharide extraction rate and quality fraction among the four methods. This method has the advantages of short extraction time, mild enzymatic hydrolysis conditions, low energy consumption, and extracts that are not easily damaged. It is a good method for extracting active ingredients from plant cells.

2 Current status of the application of astragalus polysaccharides in health drinks

2.1 Astragalus health drinks

With increasingly fierce social competition and faster and faster work rhythms, fatigue has become a common phenomenon. Health drinks that relieve fatigue, restore physical strength, and improve the body's resistance have become a research hotspot. Xu Lin et al. [20] used astragalus and medlar as raw materials, added sorbitol, concentrated kiwi juice and xanthan gum to produce a astragalus medlar compound beverage with the unique flavor of astragalus. Mao Wujing[21] used Astragalus membranaceus from Hengshan, jujube and Lu party ginseng as raw materials in a 2:2:1 ratio. By optimizing the extraction and preparation processes, two types of anti-fatigue solid drinks, granules and powders, were obtained. The formula has been shown to have significant anti-fatigue effects. Many scholars have studied the anti-aging effects of astragalus polysaccharides and developed compound astragalus anti-aging drinks, chestnut astragalus anti-oxidant drinks, astragalus rose anti-oxidant and freckle-removing drinks, etc. The development of these health drinks has provided a new path for the development and application of astragalus and its extracts.

2.2 Astragalus health yogurt

Astragalus juice has a certain antibacterial effect. Wang Dan [22] used an ultrasonic extraction method to obtain an astragalus extract, mixed it with skim milk powder and sucrose in proportion, homogenized it, added Lactobacillus bulgaricus and Streptococcus thermophilus to ferment it to obtain a health yogurt, and studied its fermentation process. The optimal fermentation process determined by response surface was: the addition of astragalus polysaccharide was 5%, the addition of sucrose was 10%, and the fermentation time was 6 h. Under these conditions, the yogurt had a good flavor and the sensory evaluation score was the highest, 88 points. Zhang Rong [23] developed a yogurt with significant hypoglycemic activity from Astragalus. The product contains 15.25% Astragalus juice, 8% maltitol, and 1.93% xylo-oligosaccharides. was 1.93%. A mixed culture of Streptococcus thermophilus, Lactobacillus bulgaricus and Bifidobacterium adolescentis was used in equal proportions, with an inoculum of 3.53% and fermentation at 43°C for 5 hours. Under these fermentation conditions, the sensory score was the highest, at 94.4 points. Studies have shown that it also has a beneficial effect on kidney and blood lipid damage.

2.3 Astragalus health tea

Astragalus tea is a major health tea variety with many benefits, including delaying aging, regulating blood sugar, improving myocardial blood supply, and boosting the immune system. Astragalus tea is easy to make, just brew with boiling water, and it is convenient to drink. There are different types, such as those made with a single herb or a blend of herbs. Cheng Likun et al. [24] developed an eight-treasure tea using astragalus, ground-cherry, black medlar, jujube, raisin, etc. as raw materials. This tea has the effect of nourishing the qi and replenishing blood, relieving summer heat and fire, and is very suitable for nursing mothers. At present, the production of health tea is relatively less mechanized, and there is still a gap between it and the requirements of standardization and industrialization. It should be actively explored to achieve the in-depth sustainable development of the health tea industry.

2.4 Astragalus health wine

Many scholars have used the soaking and blending process or the preparation process of distilled wine to develop astragalus health wine, and have achieved a series of research and development results. For example, Chai Zhi et al. [25] used sorghum and astragalus as raw materials, mixed them in a ratio of 1:9, fermented at 15 °C for 40 h, distilled, and blended to obtain a fermented distilled liquor containing astragalus total polysaccharides. Yang Lihua et al. [26] used yellow rice and glutinous rice as raw materials, added Astragalus membranaceus water extract for fermentation, and obtained Astragalus membranaceus rice wine containing polysaccharides. Feng Ziyao et al. [27] used apple pomace and chestnut residue produced during enterprise production as raw materials for enzymatic hydrolysis, fermentation and distillation, mixed them with Astragalus extract in proportion to prepare Astragalus formulated wine, which has low production cost, solves enterprise problems and provides new ideas for the development of health foods.

3 Prospects

There are many methods for extracting astragalus polysaccharides, and each method is imperfect, with its own advantages and disadvantages. Therefore, when choosing a specific method, factors such as extraction rate, difficulty of separation and purification, polysaccharide activity, equipment conditions, and extraction cost should be comprehensively considered. Studies have found that the yield of astragalus polysaccharides extracted using similar or the same method also varies greatly. Extraction conditions such as extraction time and temperature have a significant impact on the yield of polysaccharides. Therefore, after selecting a method, the extraction process should be optimized to achieve the maximum extraction rate.

The extraction of astragalus polysaccharides using the cellulase method has a high yield and stable product, and the reaction conditions are mild, energy-saving and environmentally friendly. It is a better method for extracting plant polysaccharides. It is recommended that further research be conducted to determine the optimal extraction process and formulate extraction specifications, so that this method can be better applied in large-scale industrial production.

In recent years, scholars have combined two or more modern extraction methods such as enzymatic extraction, microwave extraction, and ultrasonic extraction to extract astragaloside, which yields higher yields than a single extraction method. The monosaccharide composition and glycan structure of astragalus polysaccharides obtained by different extraction and purification methods are different, but the effects of modern extraction methods on the structural changes, stability, physiological activity and clinical efficacy of astragalus polysaccharides are still unclear.

It is recommended to strengthen in-depth research to continuously improve the extraction and purification methods to prepare high-efficiency and high-quality astragalus polysaccharides, and provide raw materials for the development of astragalus polysaccharides and related products.

A large number of studies have shown that astragalus polysaccharides have obvious physiological activities such as anti-oxidation, antibacterial, immunity enhancement, and anti-tumor. After being extracted according to the methods described in the article, they are used in health foods, and the market prospects are broad. At present, most research on astragalus health drinks focuses on new product development and process optimization, with insufficient evaluation of product functionality or testing of functional ingredients. This should be given attention in order to better promote the application of astragalus health products.

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