1 Introduction

Cordyceps polysaccharides come from various species of the Cordyceps genus, and due to their excellent medicinal value, their anti-inflammatory, anti-tumor, and immunomodulatory effects are particularly prominent. They are widely used in traditional Chinese medicine and have potential therapeutic effects in recent years (Patil et al., 2021). Cordyceps polysaccharides have attracted attention for their ability to scavenge free radicals and inhibit cancer cell growth (Šojić et al., 2022).

Traditional methods of extracting Cordyceps polysaccharides generally require the use of organic solvents, which are often time-consuming and laborious, and the purity of the extract is low. Traditional methods also fail to effectively extract all bioactive compounds, so people begin to seek more efficient and environmentally friendly extraction methods (Arumugham et al., 2021).

Supercritical fluid extraction (SFE) can quickly extract high-purity substances without the need for toxic solvents. Supercritical carbon dioxide (SC-CO₂) has low critical temperature and pressure characteristics, which can protect thermosensitive substances such as polysaccharides (Mishra et al., 2021). SFE technology has been successfully applied to extract various bioactive compounds from Cordyceps, improving polysaccharide yield and purity (Tyśkiewicz et al., 2018). This study comprehensively evaluated the application and optimization strategies of supercritical fluid technology in Cordyceps polysaccharide extraction, analyzed the key factors affecting the extraction effect, discussed how it promoted the green development of Cordyceps polysaccharide industry, and provided scientific ideas for the realization of efficient extraction and quality control of Cordyceps polysaccharide.

2 Principle and advantages of supercritical fluid technology

2.1 Basic physical and chemical properties of supercritical fluids

Supercritical fluid refers to a substance where the boundary between liquid and gas disappears at a state higher than its critical temperature and pressure. Supercritical fluids have many special properties, such as enhanced diffusion and reduced viscosity (Figure 1). Especially supercritical carbon dioxide (SC-CO₂), which has a moderate critical temperature and pressure, is non-toxic and chemically stable, and is used for extracting easily degradable compounds (Li et al., 2022).

Figure 1 A typical supercritical fluid extraction system (Adopted from Khaw et al., 2017)

2.2 Application principle of supercritical carbon dioxide (SC-CO₂)

SC-CO₂ can penetrate substances and dissolve many types of substances. By adjusting pressure, temperature, and the use of co solvents, bioactive compounds can be extracted. When extracting cordycepin and adenosine, precise control of pressure and temperature is required (Luo et al., 2017). Selective extraction of compounds using SC-CO₂ also reduces the use of harmful organic solvents (Manjare and Dhingra, 2019).

2.3 Advantages of supercritical fluid technology in the extraction of natural products

Compared to traditional extraction methods, supercritical fluid technology offers numerous advantages, including high extraction efficiency, excellent selectivity, and reduced reliance on organic solvents. It can extract heat-sensitive compounds at lower temperatures. This technology also makes it easy to remove the solvent, ensuring no residue remains in the final extract, making it an environmentally friendly and sustainable method for extracting natural products (Ya et al., 2016).

2.4 Unique applicability of technology in the extraction of Cordyceps polysaccharide

Supercritical fluid technology has special advantages in the extraction of Cordyceps polysaccharides. SC-CO₂ extraction can effectively separate Cordyceps extracts and increase the concentration of active ingredients such as polysaccharides and cordycepin (Khaw et al., 2017). The non-toxic nature of SC-CO₂ demonstrates the safety of its extract in medicinal and food applications.

3 Research progress of supercritical fluid technology in Cordyceps polysaccharide extraction

3.1 Mechanism of extracting Cordyceps polysaccharide by supercritical fluid technology

By adjusting key factors such as temperature, pressure, and co-solvents, the polysaccharides in Cordyceps can be effectively extracted. Supercritical carbon dioxide (SC-CO₂), used as the primary solvent, can penetrate Cordyceps cells at lower temperatures, releasing the polysaccharides through diffusion and cell wall rupture (Zhang et al., 2020) (Figure 2). Adding polar co-solvents like ethanol or water enhances the CO₂'s solubility of Cordyceps polysaccharides while reducing impurities. Compared to traditional extraction methods, supercritical fluid technology avoids the damage to polysaccharides caused by high temperatures and organic solvent residues.

Figure 2 Application of SFE in the mechanism of extracting cordyceps polysaccharides (Adopted from Tyśkiewicz et al., 2018)

3.2 Influence of temperature, pressure and cosolvent on the extraction efficiency of Cordyceps polysaccharide

Temperature and pressure influence the extraction efficiency and selectivity by altering the density and solubility of CO₂. Higher temperatures reduce fluid solubility but enhance polysaccharide release. However, excessively high temperatures can damage the active structure of polysaccharides, so operating conditions should be optimized to protect their activity. Increasing pressure increases fluid density, enhancing the solubility and separation efficiency of polysaccharides. The type and amount of co-solvents also significantly impact the extraction process. A small amount of polar co-solvents, such as ethanol or water, can enhance CO₂'s solubility of polysaccharides and reduce impurity interference (Liu et al., 2020).

3.3 Application of response surface method (RSM) in the optimization of Cordyceps polysaccharide extraction process

By designing experiments and establishing mathematical models, RSM can analyze the interactions among various factors to identify the optimal process conditions. In the study of Cordyceps polysaccharide extraction, RSM was used to optimize parameters such as temperature, pressure, co-solvent usage, and extraction time (Miao et al., 2022). After optimization with RSM, the extraction efficiency significantly improved, achieving a balance between polysaccharide yield and purity. Additionally, the RSM method reduces the number of experimental runs, thereby saving research costs.

3.4 Quality control and activity evaluation of Cordyceps polysaccharide after extraction

Quality control primarily involves the analysis of polysaccharides for their purity, molecular weight, and structural characteristics, typically using techniques such as high-performance liquid chromatography (HPLC), Fourier transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance (NMR) (Zhang et al., 2019). The evaluation of biological activity is a crucial aspect of researching Cordyceps polysaccharides, often validated through in vitro and in vivo experiments that assess their antioxidant, anti-inflammatory, and immune-regulating properties.

4 Key factors in the extraction process of polysaccharides from Cordyceps sinensis

4.1 The Effect of Extraction Time on the Yield and Cost of Cordyceps Polysaccharides

The extraction time directly affects the yield and extraction cost of polysaccharides. If the extraction time is too short, the release of polysaccharides is incomplete and the yield is low; However, if the extraction time is too long, although the yield increases, the energy consumption also increases, and polysaccharides may be degraded or even structurally unstable. Choosing a suitable extraction time can reduce costs while ensuring yield and purity. Through process optimization, the optimal extraction time can be found to reduce waste of resources and energy (Wan, 2015).

4.2 The Influence of Interaction of Process Parameters on the Extraction Efficiency of Cordyceps Polysaccharides

The extraction efficiency of Cordyceps polysaccharides is influenced by multiple process parameters, including temperature, pressure, cosolvent type, and dosage. By using tools such as response surface methodology (RSM), the interaction between these parameters can be analyzed to find the most suitable combination of conditions. When temperature and the amount of co solvent are used together, it can not only help polysaccharides dissolve better, but also reduce the interference of impurities (Gong et al., 2021).

4.3 Collaborative optimization of structural stability and extraction conditions of Cordyceps polysaccharides

During the extraction process, if the conditions are not suitable, it may lead to the breakage of polysaccharide molecular chains or degradation of functional groups. The extraction of temperature, pressure, and time must be optimized while ensuring structural stability. By selecting mild extraction conditions such as lower temperature and appropriate pressure, the molecular integrity and activity of Cordyceps polysaccharides can be better maintained. The selection and dosage of cosolvents are also important factors in maintaining the structure of polysaccharides (Weremfo et al., 2022).

4.4 Modeling of polysaccharide yield and purity under extraction conditions

Modeling the impact of extraction conditions on polysaccharide yield and purity is beneficial for predicting extraction results. Changes in pressure and temperature can affect the distribution of polysaccharides and other bioactive compounds in extracts (Weremfo et al., 2022). The use of SC-CO₂ grading technology can alter the distribution of polysaccharides.

5 Quality control and analysis evaluation of extracted polysaccharides

5.1 Extraction of polysaccharide purity, structure characterization and analysis methods

Commonly used analytical methods include high-performance liquid chromatography (HPLC) and high-performance thin-layer chromatography (HPTLC), which can assess the purity of polysaccharides extracted using supercritical fluid technology. HPLC has been used to achieve 98.5% and 99.2% purity of cordycepin and adenosine, respectively, from Cordyceps japonica extract (Shi et al., 2020). HPTLC is used to analyze metabolites in Cordyceps sinensis extract, producing key compounds such as cordycepin.

5.2 Biological activity assessment

The supercritical CARBON dioxide extract of Cordyceps sinensis showed a strong ability to remove free radicals, especially the graded R component, which achieved 93% removal effect on DPPH free radicals. These extracts had a protective effect on cells under low pressure and hypoxia conditions, improving cell survival rate and regulating hypoxia induced factor (Zhang et al., 2021).

5.3 Reproducibility of extraction process and product stability

Supercritical fluid extraction (SFE) technology allows for precise control over extraction parameters, such as pressure and temperature. By optimizing these parameters, the process can achieve high reproducibility. Orthogonal experimental design was used to optimize the extraction conditions of Cordyceps kyushuensis (Xu et al., 2021). Additionally, SC-CO₂, a non-toxic solvent, can reduce degradation (Zhu et al., 2016).

6 Application potential and innovative directions of 6 supercritical fluid technologies

6.1 Technical feasibility and prospects of industrial production of Cordyceps polysaccharides

Supercritical fluid extraction (SFE) technology is highly effective in extracting high-purity bioactive compounds. After enlarging the SFE process by 30 times, the optimized extraction conditions and stable process can still be maintained. The use of supercritical carbon dioxide (SC-CO₂) as a solvent has the advantages of low toxicity, easy removal, and low-temperature operation. It can not only protect the thermosensitive components in Cordyceps polysaccharides, but also reduce energy consumption and environmental pollution (Kim et al., 2024). The high selectivity and solubility of SC-CO₂.

6.2 Potential Application of Collaborative Assistance Technology in Cordyceps Polysaccharide Extraction

Combining supercritical fluid extraction (SFE) with assisted techniques such as ultrasound or microwave to disrupt Cordyceps cell walls, accelerate solute release, and increase mass transfer rates. Ultrasonic waves disrupt cell structure through cavitation effect, releasing more polysaccharide molecules; Microwaves promote the migration of intracellular substances through rapid heating and energy transfer. Although there is currently limited research on the combination of SFE and auxiliary technology for extracting polysaccharides from Cordyceps sinensis, using SFE in combination with ultrasound for plant extracts can shorten extraction time, reduce energy consumption, and improve the purity and yield of the target product.

6.3 Potential Application of Environmental Extraction Technology in Cordyceps Polysaccharide Functional Foods and Drugs

Supercritical fluid extraction (SFE) technology is particularly environmentally friendly, especially when using supercritical carbon dioxide (SC-CO₂) as a solvent, it meets the demand for sustainable practices in the production of functional foods and drugs. Cordyceps polysaccharides have significant biological activities such as antibacterial, antioxidant, and immune regulation, and have become important raw materials for developing health products. SFE technology can achieve efficient extraction of Cordyceps polysaccharides under non-toxic and green conditions. The use of SC-CO₂ for extracting Cordyceps polysaccharides not only avoids the risk of using toxic solvents in traditional methods, but also protects its thermosensitive components through low-temperature operation (Zhang et al., 2017). The Cordyceps polysaccharides extracted by SFE can be used in foods that enhance immune function, or as active ingredients in drugs for treating inflammation and anti-aging.

6.4 Extension of Extraction Process to Other Bioactive Ingredients of Cordyceps

In addition to Cordyceps polysaccharides, SFE can also be used to extract other bioactive components from Cordyceps, such as cordycepin and adenosine. SFE can efficiently extract these nucleosides with high purity and yield. Using SC-CO₂ to grade Cordyceps extract can increase the concentration of active ingredients such as polysaccharides and cordycepin, which have significant free radical scavenging and anti-tumor activity (Shan, 2024).

7 Technical Improvements and Challenges

7.1 Innovative technologies to improve extraction efficiency and selectivity

In recent years, there have been significant advances in supercritical fluid extraction (SFE) technology, with a focus on optimizing conditions to increase the efficiency and selectivity of extracting bioactive compounds from the Cordyceps genus. Orthogonal experimental design (OAD) has played a significant role in determining optimal extraction parameters such as pressure, temperature, and CO₂ flow rate, improving the yield and purity of compounds such as cordycepin and adenosine (Nguyen et al., 2020). By combining high-speed countercurrent chromatography (HSCCC) with SFE, the separation and purification of these compounds can be achieved in one step, with purities of 98.5% and 99.2%, respectively.

7.2 Green process optimization and comprehensive utilization of resources

The promotion of green extraction methods stems from the need to reduce the environmental impact of traditional solvent extraction. Supercritical CO₂ is widely used, non-toxic, and has low temperature requirements, which improves the purity of the extract and can also extract various bioactive compounds including flavonoids and bases (Qian et al., 2019).

7.3 Equipment Upgrade and Continuous Extraction Process Development for Industrial Production

In order to meet the needs of industrialization, SFE equipment has been significantly upgraded to support large-scale and continuous extraction processes. The development of a new SFE system enables the extraction process to be scaled up by 30 times while maintaining efficiency and product quality, which is crucial for the transition from laboratory scale to industrial scale (Atwi Ghaddar et al., 2023).

7.4 Technical bottleneck: Challenges of extraction efficiency and selective optimization

Despite technological advancements, there are still some challenges in improving extraction efficiency and selectivity. The distribution differences of bioactive compounds such as Cordyceps polysaccharides in different Cordyceps components are a major issue. To ensure consistency in the extraction results of different batches and Cordyceps species, it is necessary to further improve the extraction parameters and techniques (Huang, 2024).

8 Conclusion

Supercritical fluid extraction (SFE) is a promising technique for extracting bioactive compounds from the Cordyceps genus. Compared to traditional toxic solvent extraction methods, SFE is more environmentally friendly. Supercritical carbon dioxide (SC-CO₂), due to its low temperature and good diffusivity, can efficiently extract compounds with high purity. Cordycepin and adenosine have been successfully extracted and purified from Cordyceps kyushuensis. SC-CO₂ also performed graded extraction on Cordyceps sinensis, demonstrating strong free radical scavenging and anti-tumor activity.

Optimizing the SFE process is crucial for improving the extraction efficiency of valuable compounds from Cordyceps and achieving large-scale production. By precisely adjusting parameters such as pressure, temperature, and CO₂ flow rate during the extraction process, researchers can maximize the extraction efficiency and purity of the target compound. Stable production of high-quality extracts is crucial for the application of Cordyceps polysaccharides in pharmaceuticals and functional foods.

In the future, the development of SFE technology may improve the extraction efficiency of Cordyceps polysaccharides by combining other new technologies, such as high-speed countercurrent chromatography HSCCC. Exploring the combination of SFE with other extraction methods, such as subcritical water extraction, may lead to the development of more efficient and multifunctional extraction processes. Continuous research on the biological activities of Cordyceps extract, such as immune stimulation and cell protection, may further expand its application in functional foods and drugs.

Acknowledgments

We sincerely thank Dr. Zhang for his careful guidance and strong support in the research process.

Conflict of Interest Disclosure

The authors affirm that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.

References

Arumugham T.K.R., Hasan S., Show P., Rinklebe J., and Banat F., 2021, Supercritical carbon dioxide extraction of plant phytochemicals for biological and environmental applications - A review, Chemosphere, 271: 129525.

https://doi.org/10.1016/j.chemosphere.2020.129525

Atwi-Ghaddar S., Zerwette L., Destandau E., and Lesellier, E., 2023, Exploring the sequential-selective supercritical fluid extraction (S3FE) of flavonoids and esterified triterpenoids from Calendula officinalis L. flowers, Molecules, 28.

https://doi.org/10.3390/molecules28207060

Gong T., Liu S., Wang H., and Zhang M., 2021, Supercritical CO₂ fluid extraction, physicochemical properties, antioxidant activities and hypoglycemic activity of polysaccharides derived from fallen Ginkgo leaves, Food Bioscience, 42: 101153.

https://doi.org/10.1016/J.FBIO.2021.101153

Huang D.D., 2024, Molecular mechanisms of tea plant resistance to major pathogens, Molecular Pathogens, 15(1): 30-39. 

https://doi.org/10.5376/mp.2024.15.0004

Jha A., and Sit N., 2021, Comparison of response surface methodology (RSM) and artificial neural network (ANN) modelling for supercritical fluid extraction of phytochemicals from Terminalia chebula pulp and optimization using RSM coupled with desirability function (DF) and genetic algorithm (GA) and ANN with GA, Industrial Crops and Products, 170: 113769.

https://doi.org/10.1016/J.INDCROP.2021.113769

Khaw K., Parat M., Shaw P., and Falconer J., 2017, Solvent supercritical fluid technologies to extract bioactive compounds from natural sources: a review, Molecules : A Journal of Synthetic Chemistry and Natural Product Chemistry, 22(7): 1186.

https://doi.org/10.3390/molecules22071186

Kim D., Hồng N., and Nhu N., 2024, Optimization of adenosine và cordycepin extraction from cordyceps. Heavy metals and arsenic concentrations in water, agricultural soil, and rice in Ngan Son district, Bac Kan province, Vietnam.

https://doi.org/10.47866/2615-9252/vjfc.4363

Li L., But G., Zhang Q., Liu M., Chen M., Wen X., Wu H., Cheng H., Puno P., Zhang J., Fung H., Bai S., Wong T., Zhao Z., Cao H., Tsim K., Shaw P., Han Q., and Sun H., 2021, A specific and bioactive polysaccharide marker for Cordyceps, Carbohydrate Polymers, 269: 118343.

https://doi.org/10.1016/j.carbpol.2021.118343

Li L., Chen M., Zeng Y., and Liu G., 2022, Application and perspectives of supercritical fluid technology in the nutraceutical industry, Advanced Sustainable Systems, 6(7): 2200055.

https://doi.org/10.1002/adsu.202200055

Liu Y., Li Y., Zhang H., Li C., Zhang Z., Liu A., Chen H., Hu B., Luo Q., Lin B., and Wu W., 2020, Polysaccharides from Cordyceps miltaris cultured at different pH: Sugar composition and antioxidant activity, International Journal Of Biological Macromolecules, 162: 349-358.

https://doi.org/10.1016/j.ijbiomac.2020.06.182

Luo X., Duan Y., Yang W., Zhang H., Li C., and Zhang J., 2017, Structural elucidation and immunostimulatory activity of polysaccharide isolated by subcritical water extraction from Cordyceps militaris, Carbohydrate Polymers, 157: 794-802.

https://doi.org/10.1016/j.carbpol.2016.10.066

Manjare S., and Dhingra K., 2019, Supercritical fluids in separation and purification: a review, Materials Science for Energy Technologies, 2(3): 463-484.

https://doi.org/10.1016/j.mset.2019.04.005

Miao M., Yu W., Li Y., Sun Y., and Guo S., 2022, Structural elucidation and activities of Cordyceps militaris-derived polysaccharides: a review, Frontiers in Nutrition, 9: 898674.

https://doi.org/10.3389/fnut.2022.898674

Mishra J., Khan W., Ahmad S., and Misra K., 2021, Supercritical carbon dioxide extracts of Cordyceps sinensis: chromatography-based metabolite profiling and protective efficacy against hypobaric hypoxia, Frontiers in Pharmacology, 12: 628924.

https://doi.org/10.3389/fphar.2021.628924

Nguyen N., Nguyen V., Nguyen M., Thanh L., Phuong T., and Duong D., 2020, Screening of extraction conditions by Plackett–Burman design for extraction of Cordyceps militaris Cordycipitaceae, IOP Conference Series: Materials Science and Engineering, 991: 012017.

https://doi.org/10.1088/1757-899X/991/1/012017

Patil P., Patil S., Kelkar R., Patil N., Pise P., and Nadar S., 2021, Enzyme-assisted supercritical fluid extraction: an integral approach to extract bioactive compounds, Trends in Food Science and Technology, 116: 357-369.

https://doi.org/10.1016/J.TIFS.2021.07.032

Qian Z., Li C., Song Y., Zhou M., and Li W., 2019, Rapid determination of adenosine in Cordyceps by online extraction HPLC, Journal of Chromatographic Science, 57(4): 381-384.

https://doi.org/10.1093/chromsci/bmz007

Shan P., 2024, Research on the relationship between genome stability of grassland plants and ecosystem immunity, International Journal of Molecular Ecology and Conservation, 14(1): 1-9.

https://doi.org/10.5376/ijmec.2024.14.0001

Shi K., Yang G., He L., Yang B., Li Q., and Yi S., 2020, Purification, characterization, antioxidant, and antitumor activity of polysaccharides isolated from silkworm cordyceps, Journal of Food Biochemistry, e13482.

https://doi.org/10.1111/jfbc.13482

Šojić B., Putnik P., Danilović B., Teslić N., Kovačević B., and Pavlić B., 2022, Lipid extracts obtained by supercritical fluid extraction and their application in meat products, Antioxidants, 11(4): 716.

https://doi.org/10.3390/antiox11040716

Tyśkiewicz K., Konkol M., and Rój E., 2018, The application of supercritical fluid extraction in phenolic compounds isolation from natural plant materials, Molecules : A Journal of Synthetic Chemistry and Natural Product Chemistry, 23(10): 2625.

https://doi.org/10.3390/molecules23102625

Weremfo A., Abassah-Oppong S., Adulley F., Dabie K., and Seidu-Larry S., 2022, Response surface methodology as a tool for optimization of the extraction of bioactive compounds from plant sources, Journal of the Science of Food and Agriculture, 103(1): 26-36.

https://doi.org/10.1002/jsfa.12121

Xu J., Tan Z., Shen Z., Shen X., and Tang S., 2021, Cordyceps cicadae polysaccharides inhibit Human cervical cancer Hela cells proliferation via Apoptosis and Cell Cycle Arrest, Food and Chemical Toxicology : An International Journal Published for the British Industrial Biological Research Association, 111971.

https://doi.org/10.1016/j.fct.2021.111971

Ya Y., Zheng L., Hui Z., Di Z., Hong C., Jia W., and Qing D., 2016, Study on the optimization for the extraction and antioxidant activity of polysaccharide from cordyceps militaris by subcritical water, Science and Technology of Food Industry, 252-257.

Zhang J., Wen C., Duan Y., Zhang H., and Ma H., 2019, Advance in Cordyceps militaris (Linn) Link polysaccharides: Isolation, structure, and bioactivities: A review.. International journal of biological macromolecules, 132, 906-914.

https://doi.org/10.1016/j.ijbiomac.2019.04.020

Zhang W., Li B., Dong X., Wang B., and Wu Z., 2017, Enzyme-assisted extraction of cordycepin and adenosine from cultured Cordyceps militaris and purification by macroporous resin column chromatography, Separation Science and Technology, 52: 1350-1358.

https://doi.org/10.1080/01496395.2017.1287736

Zhang X., Zhang X., Gu S., Pan L., Sun H., Gong E., Zhu Z., Wen T., Daba G., and Elkhateeb W., 2021, Structure analysis and antioxidant activity of polysaccharide-iron (III) from Cordyceps militaris mycelia, International Journal of Biological Macromolecules, 178: 170-179.

https://doi.org/10.1016/j.ijbiomac.2021.02.163

Zhang Y., Zeng Y., Cui Y., Liu H., Dong C., and Sun Y., 2020, Structural characterization, antioxidant and immunomodulatory activities of a neutral polysaccharide from Cordyceps militaris cultivated on hull-less barley, Carbohydrate Polymers, 235: 115969.

https://doi.org/10.1016/j.carbpol.2020.115969

Zhu Z., Dong F., Liu X., Lv Q.Y., Liu F., Chen L., Wang T., Wang Z., and Zhang Y., 2016, Effects of extraction methods on the yield, chemical structure and anti-tumor activity of polysaccharides from Cordyceps gunnii mycelia, Carbohydrate Polymers, 140: 461-471.

https://doi.org/10.1016/j.carbpol.2015.12.053