Medicinal Plants Collection and Drying Techniques

Collection and Drying of Medicinal Plants

• Medicinal plants must be collected at the optimal time and stage of development to ensure maximum quality and quantity of active constituents.

Time of Collection

• Time of Year: The amount and nature of active constituents vary throughout the year. For example, rhubarb contains no anthraquinones in winter, but instead anthranols, which convert to anthraquinones in summer.
• Time of Day: The percentage of certain compounds, like cardiac glycosides in Digitalis leaves, is higher when collected in the afternoon than the morning. These glycosides decompose at night but recombine during the day with sugars from photosynthesis. Solanaceous leaves contain higher alkaloids when collected in the morning.

Stage of Development

• General Principle: The percentage of active constituents in a drug depends on the maturity and age of the plant.
• Example: Solanaceous leaves: Contain maximum alkaloids at the flowering stage. Santonica flowers contain the bitter principle santonin when not expanded, with the amount of santonin decreasing as the flowers expand.
• Leaves: Collected at the beginning of the flowering stage, when they are in the healthiest state and contain the optimal percentage of active constituents. Collection should be in dry weather to prevent deterioration or discoloration.
• Flowers: Collected at the optimal stage of pollination but before fruits form. Clove buds are collected while chamomile are collected after the flowers are fully expanded.
• Barks: Collected during spring or early summer when the cambium is active and can easily be stripped from the trunk or branches. Longitudinal incisions are usually made at intervals, then round incisions are made and the bark is stripped off in long pieces.
• Fruits: Collected near the ripening stage, when fully mature but not fully ripened. They must be collected in dry weather.
• Seeds: Collected at the ripening stage, with mature seeds separated from the pericarp.
• Underground Organs: Collected in autumn or winter(roots, rhizomes, bulbs, corms)

Drying of Crude Drugs

• Treatment before Drying: Cleaning and garbling are crucial preliminary steps before drying. Cleaning involves removal of soil particles from underground organs by shaking, brushing, or washing. Garbling is getting rid of foreign material, such as sand or other plant parts, by hand or specialized machinery.
• Moisture removal: Important for stopping enzymatic action, preventing microorganism growth (bacteria and fungi), facilitating grinding and handling, enabling easier packing and storage, and lowering transportation costs.
• Duration: Fresh plants contain high moisture content (up to 80-90%), and drying takes anywhere from a few hours to many weeks.
• Factors for Appropriate Drying Processes: The optimal temperature and speed for drying depend on the plant and the desired outcome. If enzymes need to be active, a slower drying process is required. Quickly drying plants will help maintain the contents that are undesirable to lose. Drying must be done with care to maintain the physical properties and chemical constituents of the drug. The goal is to retain physical characteristics, chemical constituents, and meet pharmacopoeia requirements for maximal moisture content.

Ideal Drying Practices

• Natural Drying: Done by natural air in sun or shade. Suitable for plants that are not affected by direct sunlight, such as Senna leaves. This is a slow process.
• Artificial Drying: Faster and suitable for some delicate plants. Different types are used depending on the specific need.
• Direct Fire/Stoves: Careful application, as the active compounds can be impacted.
• Drying Chambers: A controlled environment for drying, using warm air flowing through the system to remove moisture.
• Vacuum Drying: Preserves delicate plants sensitive to high temperatures. Airtight chambers connected to a vacuum pump. The vacuum decreases pressure to remove water more rapidly under low temperatures.
• Freeze Drying (Lyophilization): Best suited for delicate plants. Water is removed from the frozen state through sublimation.

Drying's Impact on Crude Drugs

• Size & Weight: Drugs shrink and lose about 80-90% of their original weight.
• Shape & Appearance: Drugs shrink, and the surface shows wrinkles or reticulation. The inner tissues are often softer than the outer tissues.
• Texture: Fresh organs are typically firm, while dried plants become harder.
• Color: Drugs usually become darker during drying. Some colors change completely. Loss of color due to chlorophyll breakdown in some instances.
• Odor: The odor may diminish, change, or develop as a result of drying. Certain aromatic plants develop characteristic fragrances due to the breakdown of compounds.
• Taste: Taste can change during drying, becoming more or less pleasant.
• Constituents: Drying may affect the active constituents in desirable or undesirable ways. The process may encourage or disallow the production of certain chemical compounds.

Storage of Drugs

• General Principle: Proper storage is required for the drugs to maintain their qualities for optimal use as part of the medicine.
• Quality deterioration: When drugs are stored in inappropriate conditions, they may eventually lose their qualities.
• Undesirable changes: Some drugs undergo undesirable changes during storage such as, loss of aroma in aromatic drugs or developing a bad odor in ergot. Fixed oils may turn rancid, while volatile oils may resinify.
• Loss of active constituents: Digitalis and Cannabis might lose active constituents during storage.

Factors for Deterioration

• Physicochemical Factors:
• Moisture: Causes hydrolysis of active constituents, leading to enzyme activity and fungal growth.
• Temperature: Slight increase in temperature accelerates enzymatic action, especially significant for volatile oils—these break down more easily with increases in temperature.
• Light: Degrades delicate substances like rose petals and Digitalis leaves. The process is often influenced as UV light degrades materials.
• Air (Oxygen): Causes oxidation, decreasing or changing the chemical constituents of the drugs.
• Biological Factors:
• Molds/Fungi: Attack drugs containing nutritive substances (roots/bulbs).
• Insects: Commonly found on powdered drugs, reducing suitability for extracts.
• Rodents: Commonly found in the storage structures of medicines.
• Methods of Controlling Insects: Heating drugs, fumigation (e.g. using various insecticides), or applying lime, which impedes the insects’ respiratory systems.
• Low Temperature Storage: Used for controlling the factors leading to biological deterioration.