Extraction Process 01: Solvent Extraction

1. Concept:

• Solvent Extraction (S.E.): The process of extracting active compounds from medicinal plants using a suitable solvent. This process is often not complete, meaning there are still undissolved residues in the solvent.

• Extract: The solvent after it has dissolved the soluble components from the medicinal plant.

• Active Compound: The substance with pharmacological activity, which is the target for extraction from the medicinal plant.

• Impurities: Substances that do not have pharmacological activity, which can hinder product preservation and processing, as well as affect the effectiveness of the active compound.

• Marc: The remaining part of the medicinal plant after complete extraction.

2. Role of S.E.:

• Separation, Isolation, Identification, and Purification: S.E. is the first step in the research and processing of medicinal plants. It helps to extract the active compound from the medicinal plant, isolate different components, identify the chemical composition of the medicinal plant, and purify the obtained active compound.

3. Requirements for Solvents:

The ideal solvent in S.E. needs to meet the following requirements:

• High Penetration: Penetrate deep into the medicinal plant to effectively contact the active compound.

• Selective Dissolution: Primarily dissolve the desired active compound, limiting the dissolution of impurities.

• Chemically Inert: Do not react with the components of the medicinal plant or the active compound.

• No Unusual Taste or Odor in the Final Product: The solvent does not leave a strange taste or smell in the final product.

• Easily Volatile: Easy to remove the solvent after extraction.

• Low Toxicity: Safe for users and the environment.

• Affordable: Reasonable cost for large-scale application.

• Readily Available: Easy to purchase and use.

4. Commonly Used Solvents:

• Water: Used to dissolve compounds with hydrophilic properties like alka-salts, glycosides, sugars, inorganic salts-acids.

• Ethanol: Used to dissolve compounds with lipophilic properties like alka-bases, glycosides, essential oils, resins.

• Glycerin: Used to dissolve tannins.

• Organic Solvents (OS): Used to dissolve compounds that are difficult to dissolve in water, such as male fern extract (ether).

• Vegetable Oils (VO): Used to dissolve essential oils and fats.

5. Characteristics of Water as a Solvent:

• Distilled water, demineralized water, soft water: Do not contain Ca or Mg ions to avoid forming salts or precipitates with the active compound.

• Advantages: Low viscosity, low surface tension, good solubility for hydrophilic compounds, readily available and inexpensive.

• Disadvantages: Broad solubility range, creates an environment conducive to mold and bacterial growth, high boiling point, can degrade some active compounds.

6. Advantages and Disadvantages of Ethanol as a Solvent:

• Advantages: Selective dissolution capability (depending on the alcohol concentration), infinitely soluble in water, long preservation (>20%), low boiling point (78°C), impurity removal, does not swell the medicinal plant, acidifies the environment, increasing extraction efficiency.

• Disadvantages: Flammable and explosive, toxic.

7. Characteristics of VO as a Solvent:

• Peanut, sesame, sunflower oils: Used to dissolve essential oils and fats.

• Advantages: Good solubility for lipophilic compounds.

• Disadvantages: High viscosity, prone to degradation and oxidation.

8. Basis of S.E.:

• Mass transfer process between two phases (R/L) across the cell membrane of the medicinal plant: This process includes the following steps:

• Osmosis: The solvent moves across the cell membrane from a high concentration area to a low concentration area.

• Dissolution: The active compound is dissolved in the solvent.

• Diffusion: The active compound moves from the cell into the solvent.

• Osmosis across the plasmatic membrane: The active compound moves across the cell membrane to enter the extract.

9. Factors that Promote Osmosis:

• Vacuum: Creates a vacuum environment outside to draw water out of the cell.

• Increasing Liquid Pressure: Increases the liquid pressure outside to force water out of the cell.

• Replacing Air in Capillaries: Replacing air in the capillaries of the medicinal plant with gas that easily dissolves in the solvent.

• Using Surfactants: Reduces the surface tension of the solvent, allowing it to penetrate deeper into the medicinal plant.

10. Nature of Internal Diffusion and External Diffusion:

• Internal Diffusion: This is a molecular diffusion process where the active compound moves across the intact cell membrane, resulting in selectivity.

• External Diffusion: This is a free diffusion process where the active compound moves freely in the solvent after the cell is disrupted.

11. Factors Affecting Diffusion:

• Medicinal Plant: Type of medicinal plant, particle size, cell structure…

• Solvent: Type of solvent, solvent concentration, solvent temperature…

• Technique: Extraction method, extraction time…

12. Purpose and Regulations of Sieving:

• Purpose: To separate powders with different particle sizes after grinding, helping to improve extraction efficiency.

• Pharmacopoeia regulations specify 12 sieve sizes and 5 powder sizes: Each sieve and powder size corresponds to a specific particle size.

13. Maximum Soaking Time for Different Solvents:

• Water: 48 hours.

• Alcohol: Can be over 7 days.

• Soaking time depends on the type of solvent: Each solvent has its own optimal soaking time.

14. Extraction Methods:

• Cold Maceration: Soaking the medicinal plant in the solvent at room temperature for several days. Applicable for easily soluble compounds, compounds that are easily thermolyzed, medicinal plants without cell structure, the commonly used solvent is an EtOH-water mixture.

• Decoction: Soaking the medicinal plant in the solvent at a temperature lower than the solvent’s boiling point but higher than the ambient temperature. Applicable for compounds that are poorly soluble at room temperature, easily thermolyzed, solvents with high viscosity (VO).

• Infusion: Soaking the medicinal plant in boiling solvent for 15-30 minutes, then pressing to obtain the extract. Applicable for delicate medicinal plants, compounds that dissolve in a short time at high temperatures, the solvent is water.

• Percolation: Boiling the medicinal plant in the solvent. Applicable for solid medicinal plants, less prone to thermolyzation, the solvent is water.

• Continuous Extraction: The solvent flows slowly through the medicinal plant, constantly in contact with the solvent, creating a concentration gradient, allowing for complete extraction of the active compound.

• Equipment: Cylindrical vessel, truncated conical vessel.

• Advantages: Complete extraction of the active compound, obtaining a concentrated extract, low solvent consumption.

• Disadvantages: Not applicable for aqueous solvents, not applicable for medicinal plants with high starch, mucilage, or gum content.

Note:

• The choice of extraction method depends on the type of medicinal plant, the active compound to be extracted, and the product requirements.

• It is essential to check the solubility, boiling point, and chemical properties of the solvent before using it.

• Follow safety regulations when handling solvents and performing extraction procedures.

Additional Information:

• Soxhlet Method: This is a continuous extraction method that uses hot solvent to extract active compounds from medicinal plants. This method is highly efficient and widely used in laboratories.

• Ultrasonic Method: Utilizes ultrasonic waves to enhance diffusion and osmosis, shortening extraction time and improving extraction efficiency.

• Supercritical CO2 Extraction: Uses supercritical CO2 to extract the active compound. This method is environmentally friendly and highly efficient.

Conclusion:

Solvent extraction is a vital technique in the research and processing of medicinal plants. Selecting the appropriate solvent and efficient extraction method is crucial for the quality of the final product.