Extraction Methods in Herbal Medicine

Plant Extracts and Herbal Preparations

• Extraction procedures are methods for obtaining plant extracts
• Many procedures exist, including:
  • Maceration
  • Infusion
  • Percolation
  • Digestion
  • Decoction
  • Continuous hot extraction
  • Solvent-solvent precipitation
  • Liquid-liquid extraction
  • Distillation
  • Specific procedures

Maceration

• Involves placing a crude drug (whole or powdered) in a stoppered container with a solvent and allowing to stand at room temperature for at least 3 days with frequent agitation.
• The mixture is strained, marc (solid material) is pressed, and the liquid is clarified by filtration or decantation.
• Advantage: no degradation of extracted products since no heat is used.
• Disadvantage: not all compounds can be extracted.

Infusions

• The plant material is left to soak in a pre-heated solvent (e.g., hot water) at room temperature.
• The plant debris is separated from the solvent.
• Can be done with or without intermittent stirring.

Digestion

• Similar to maceration but gentle heat is used during extraction.
• Increases solvent efficiency.

Decoction

• Boiling the crude drug in a specified volume of water for a defined time.
• The mixture is then cooled and strained or filtered.
• Suitable for extracting water-soluble and heat-stable constituents.

Percolation

• The material is packed in a column with a filter to prevent solid material escape.
• The solvent (room temperature) is poured on top and allowed to trickle through the plant material.

Continuous Hot Extraction (Soxhlet)

• Uses Soxhlet apparatus to continuously extract plant material with a solvent.
• Plant material is placed in a porous thimble.
• The solvent is boiled and flows through the thimble, extracting plant material, and then collecting in a flask.
• Repetitive process, solvent continuously extracts material.

Solvent-Solvent Precipitation

• Dissolving an extract in a suitable solvent, then mixing with another less polar solvent.
• This causes the precipitation of less soluble components.

Steam Distillation

• Method for extracting volatile oils from plants
• Plant material is mixed with water and heated to boiling.
• The emergent vapors are collected and condensed, separating the oil from the water.
• Can be direct, using steam from a separate generator.

Disadvantages of Distillation

• High temperatures in the presence of water can cause hydrolysis of esters, removal of water soluble compounds, and loss of volatile components.

Volatile Oils

• Obtained by steam distillation or pressing.
• Some types include Musk, from deer; Amber, from whale.

Methods of Volatile Oil Preparation

• Hydrodistillation
• Scarification/Expression
• Extraction with solvents
• Enzymatic hydrolysis
• Supercritical methods
• Method choice depends on plant material condition, oil location, oil amount, and oil constituent nature.

Hydrodistillation (Details)

• The principle is that a mixture of water and immiscible volatile oil boils at a lower temperature than water's boiling point.
• The boiling point of turpentine oil is about 160° C, but when mixed with water and heated, the mixture boils at around 95.6°C.
• The choice of method depends on plant condition and oil location.
• Three types exist.

Water Distillation

• Direct mixing of plant material and water directly in a still pot.

Water and Steam Distillation

• Plant material placed on a perforated screen above the still's bottom to prevent direct water contact.

Direct Steam Distillation

• No water in the bottom of the still
• Steam from separate generator directly passes through plant material.

The Oil Separator

• Separates oil from water after condenser passage.
• Usually done with a Florentine receiver, separating lighter than water oils.

Cohobation (Redistillation of Water)

• The distillation water, containing trace amounts of dissolved volatile oil, is returned to the distillation still to recover the oil.

Alkaloids

• Plant compounds that are basically in nature, derived from amino acids present in plants.
• Contain one or more nitrogen atoms (usually in a heterocyclic ring).
• Have marked physiological action on humans or animals.

Differences from Alkaloids

• Some alkaloids may not be basic.
• The nitrogen atom in some alkaloids might not be part of a heterocyclic ring.

Types of Alkaloids

• True alkaloids: Nitrogen part is part of heterocyclic ring. Derived amino acid.
• Proto alkaloids: Do not have heterocyclic ring with nitrogen but derived from nitrogenous compounds.
• Pseudo alkaloids: Nitrogen is part of heterocyclic ring but not derived from amino acids.

Distribution of Alkaloids

• Found in higher plants (10-25%).
• Dicots tend to have more alkaloids than monocots.
• Families rich in alkaloids (e.g., Apocynaceae, Loganiaceae, Liliaceae, Rubiaceae, Solanaceae, Papaveraceae).

Function of Alkaloids in Plants

• Protective against insects/herbivores (bitter taste).
• Nitrogen source in nitrogen deficiency cases.
• Growth regulators in certain metabolic systems.
• Energy source in carbon dioxide assimilation deficiency.

Glycosides

• Organic compounds with a sugar portion (glycoside) attached to a non-sugar component (aglycone or genin).
• Usually aromatic in nature
• Hydrolyzed by acid, alkali, or enzymes.

Glycosides in Plants

• Occur in small amounts in plants, fungi, and animals.
• Can be used for detoxifying materials.
• Some used for transferring water-insoluble components.
• Act as energy sources, storing harmful products, and aiding in regulation (growth) and coloration.
• Some have antibacterial activity to protect from bacteria and diseases.
• Formed by biochemical reactions transforming water-insoluble compounds into more polar water soluble molecules.

Test your knowledge on various extraction methods used in herbal medicine. This quiz covers techniques such as decoction, maceration, and Soxhlet extraction, along with their advantages and disadvantages. Understand the specific applications of these methods in extracting plant constituents effectively.