INTRODUCTION:
Extraction1 is a fundamental process in pharmaceutical, nutraceutical and traditional medicine systems. It involves the separation of bioactive constituents using appropriate solvents or techniques aiming to obtain concentrated, stable and efficacious therapeutic products. In phytochemistry and pharmacognosy, the choice of extraction method significantly impacts the chemical profile, potency and stability of the final preparation.
Extraction methods can be broadly classified into conventional and non-conventional techniques2. Conventional techniques include maceration, infusion, percolation, decoction, Soxhlet extraction, hydro-distillation and steam distillation. Non-conventional techniques comprise supercritical fluid extraction (SFE), ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE), accelerated solvent extraction (ASE), enzyme-assisted extraction (EAE), microwave hydro-diffusion and gravity (MHG), pulsed electric field extraction (PEF) and subcritical water extraction (SWE). Emerging techniques include natural deep eutectic solvent (NADES)-based extraction, pressurized hot water extraction (PHWE), flash extraction, ohmic heating-assisted extraction (OHAE), enzyme ultrasound synergistic extraction (EUSE) and ionic liquid-based extraction (ILBE) which focus on greener, more efficient and sustainable extraction processes.
The extraction process is crucial for isolating volatile compounds such as essential oils3, alkaloids, phenolics and glycosides which are responsible for the pharmacodynamic action of many herbal formulations. Particularly for aromatic and medicinal plants, volatile oils comprising monoterpenes, sesquiterpenes, alcohols, aldehydes and esters are isolated using methods like hydro-distillation and steam distillation. These oils are known for their antimicrobial, anti-inflammatory, antioxidant and anxiolytic properties making their extraction a key area in natural product research and formulation.
In Ayurvedic pharmaceutics, various kalpanas or dosage forms are formulated to effectively extract and deliver the therapeutic constituents of medicinal substances. The foundational extraction techniques are grouped under panchavidha kashaya kalpana4, which include swarasa (juice), kalka (paste), kwatha (decoction), hima (cold infusion), and phanta (hot infusion). These are primarily aqueous-based preparations. Supporting these are upakalpanas, which are auxiliary or preparatory processes that help refine and enhance the efficacy of the main formulations. In addition to these, several other kalpanas involve different extraction methods suited to specific types of active principles. These traditional formulations reflect the sophisticated understanding of extraction techniques in ancient Ayurveda. However, with advancements in dosage form development and the need for increased efficacy, reduced dosage volume, better stability and improved palatability, new types of formulations evolved. Among these, Arka Kalpana5 refers to a specialized process of preparing Arka distillate obtained by controlled heating and condensation of herbal, mineral or animal substances in a vessel known as Arka Yantra. This method extracts the volatile and subtle constituents of the drugs and results in a clear, aromatic, water-based product that is refined and highly bioavailable.
Given the contemporary need to integrate traditional wisdom with modern analytical precision, this review aims to critically evaluate current extraction procedures. Specifically, it compares various conventional and modern techniques for volatile and hydroalcoholic extract preparations.
MATERIALS AND METHODS:
Relevant peer-reviewed journal articles, authoritative textbook published in the last two decades were systematically reviewed through database searches (PubMed, Scopus, Google Scholar) to ensure comprehensive coverage of both traditional and emerging techniques.
Techniques such as maceration, infusion, decoction, percolation, Soxhlet extraction and the Ayurvedic Panchavidha Kashaya Kalpana, Arka Kalpana were included to represent classical and culturally significant practices. Meanwhile, advanced methodologies like SFE, UAE and EUSE reflect the evolving landscape of phytopharmaceutical processing. The selection criteria emphasized reproducibility, extraction efficiency, solvent compatibility and relevance to research and small-scale formulation development. The following sections describe each method in detail, highlighting their mechanisms, practical applications and limitations based on current literature and Industrial practices.
1. Conventional Extraction Techniques:
1.1 Maceration6
Maceration is one of the oldest and simplest methods used to extract bioactive compounds from plant material. In this technique, the crude drug is immersed in a solvent (commonly water, ethanol or a hydroalcoholic mixture) at room temperature for several days. The plant material is usually crushed to increase surface area and maximize solvent penetration. During this period, the solvent dissolves the active constituents, forming a concentrated extract. Occasional agitation helps improve the extraction rate. After the stipulated time (ranging from 3 to 7 days), the mixture is filtered to separate the extract from the plant residue. This method is particularly useful for heat-sensitive compounds and soft plant parts. However, it has limitations such as lower efficiency and longer processing time compared to modern techniques. It is often used in small-scale herbal preparations and traditional medicine practices. Maceration is economical and requires minimal equipment, making it a widely used technique in many developing countries.
1.2 Infusion7:
Infusion is a method that closely resembles the way tea is prepared, typically used for soft plant parts like leaves, flowers and green stems. The technique involves adding hot water to the plant material and allowing it to steep for a short time, usually 15 to 30 minutes. This method is ideal for extracting water-soluble and heat-stable constituents such as flavonoids, tannins and glycosides. After steeping, the liquid is filtered and consumed or processed further. Infusion is easy to perform and requires only basic tools such as a kettle or covered vessel. It is frequently used in herbal medicine to prepare soothing, aromatic, and mild remedies. Though simple, the method is not suitable for hard or woody plant parts and yields a lower concentration of extracts compared to percolation or Soxhlet methods. Nonetheless, it is widely practiced in traditional systems due to its speed, convenience and palatability.
1.3 Percolation8:
Percolation is an exhaustive extraction process that involves the slow passage of solvent through a packed column of powdered plant material. A cylindrical vessel known as a percolator is used, into which the powdered crude drug is evenly packed. The solvent is added from the top and allowed to flow through by gravity. The extract is collected from the bottom over a period of hours or days until all soluble constituents are removed. Unlike maceration, percolation ensures a more complete extraction and is better suited for large-scale pharmaceutical use. It is especially effective for extracting alkaloids, glycosides and other moderately polar to polar phytochemicals. This method maintains a constant concentration gradient, which Favors continuous diffusion of solutes into the solvent. The process may require optimization of variables such as particle size, solvent polarity and flow rate.
1.4 Decoction:9
Decoction is a method that uses boiling to
extract active ingredients from tough or woody plant materials such as roots,
bark and seeds. The crude drug is usually coarsely powdered and boiled in water
for 15–60 minutes. The mixture is then cooled and filtered to obtain the
decoction. This technique allows the breakdown of rigid cell walls and releases
compounds that are not extractable through simple maceration or infusion.
Decoctions are often used in Ayurveda and traditional Chinese medicine for
preparing formulations like Kwatha. The high temperature may degrade
heat-sensitive constituents but is beneficial for obtaining alkaloids, bitters
and polysaccharides. Decoctions should be consumed within a short time frame
due to microbial growth. Despite modern alternatives, decoction remains a
preferred method for preparing household remedies and traditional formulations.
1.5 Soxhlet Extraction:10
Soxhlet extraction is a laboratory-based technique used for efficient and continuous extraction of compounds using an organic solvent. It is particularly effective for thermostable compounds. In this method, the solvent is repeatedly vaporized, condensed and siphoned through the plant material. This allows thorough washing of the material without the need to replenish the solvent manually. Soxhlet apparatus comprises a distillation flask, extraction chamber and condenser. The method is advantageous in terms of completeness of extraction and solvent recycling. However, it requires heat, time and proper solvent selection. Soxhlet is widely used for lipid, alkaloid and resin extraction in both analytical and industrial settings.
2.Non-Conventional Extraction Techniques:
2.1 Supercritical Fluid Extraction (SFE):11
Supercritical fluid extraction employs gases (commonly CO₂) in a supercritical state, where they possess properties of both liquids and gases. In this state, CO₂ acts as a highly selective solvent that can extract non-polar and thermolabile compounds efficiently. This method operates under specific temperature (31°C) and pressure (74 bar) conditions and the extracted material contains no residual solvents, making it ideal for food and pharmaceutical applications. The process is also customizable: modifiers like ethanol can be added to extract polar compounds. SFE is used for obtaining high-purity extracts. Though equipment and operational costs are high, its eco-friendliness, efficiency and scalability make it a preferred green technology in modern industries.
2.2 Ultrasound-Assisted Extraction (UAE):12
Ultrasound-Assisted Extraction utilizes high-frequency sound waves (typically 20–100 kHz) to enhance the extraction of bioactive compounds from plant materials. These sound waves create cavitation bubbles in the solvent, which collapse violently and generate localized high temperatures and pressures. This disrupts plant cell walls, increasing solvent penetration and mass transfer of solutes into the solvent. UAE is effective at low temperatures, making it suitable for thermolabile compounds such as polyphenols, flavonoids, and essential oils. The technique is relatively quick and requires minimal solvent, aligning with green chemistry principles. UAE has been widely used for extracting compounds from ginger, garlic, and citrus peels. Although it offers excellent energy efficiency and is easy to integrate with other methods, limitations include uneven distribution of ultrasonic energy in large volumes and possible degradation of sensitive constituents if parameters are not properly optimized.
2.3 Microwave-Assisted Extraction (MAE):13
Microwave-Assisted Extraction uses microwave energy (typically 300 MHz to 300 GHz) to rapidly heat the solvent and plant matrix, causing cell rupture and improved diffusion of intracellular compounds. The technique relies on the dipolar rotation and ionic conduction of polar solvents and solutes, leading to selective heating. MAE significantly reduces extraction time and solvent use, making it suitable for thermolabile and moderately polar compounds such as alkaloids, saponins, and phenolics. It has been successfully applied to extract active ingredients from plants like turmeric, green tea, and Eucalyptus. The main advantages include uniform heating, enhanced yield, and ease of scaling up. However, it may not be ideal for non-polar solvents or compounds and requires specialized microwave reactors to avoid overheating and degradation.
2.4 Accelerated Solvent Extraction (ASE):14
Accelerated Solvent Extraction, also known as Pressurized Liquid Extraction, employs elevated temperatures (50–200°C) and pressures (10–20 MPa) to maintain the solvent in a liquid state above its boiling point. This increases the solubility and diffusion rate of solutes, allowing faster and more exhaustive extraction. ASE is particularly effective for lipophilic compounds like sterols, carotenoids, and fatty acids. It is widely used in environmental, food, and pharmaceutical analysis. The method allows precise control of temperature, pressure, and solvent volume, leading to reproducible results. Although ASE offers high throughput and automation compatibility, the need for costly instrumentation and risks of compound degradation at high temperatures are its main limitations.
2.5 Enzyme-Assisted Extraction (EAE):15
Enzyme-Assisted Extraction employs hydrolytic enzymes such as cellulases, pectinases, and proteases to degrade plant cell walls and release bound phytoconstituents. The method works under mild conditions (30–50°C) and is ideal for polysaccharides, phenolics, and glycosides. EAE improves yield by increasing cell permeability and breaking down complex matrices. It is especially useful for hard tissues like seeds and peels. Enzymatic pre-treatment is eco-friendly and can be combined with techniques like ultrasound or microwave for synergistic effects. EAE has been effectively applied in extracting compounds from soya, pomegranate, and citrus waste. Challenges include enzyme cost, activity optimization, and the need to inactivate enzymes post-extraction.
2.6 Microwave Hydro-Diffusion and Gravity (MHG):16
Microwave Hydro-Diffusion and Gravity is a solvent-free microwave-based technique that facilitates the diffusion of volatile compounds from plant tissues using gravity. In MHG, fresh plant material is heated by microwave irradiation without any added solvent, causing internal moisture to act as an extraction medium. Volatile compounds are carried by this moisture to a condenser, where they are collected as distillate. MHG is particularly suited for essential oils and aromatic compounds from fresh herbs like rosemary, lavender, and basil. The method is fast, energy-efficient, and avoids solvent use entirely. However, it requires specific microwave-compatible equipment and is not suitable for dry or non-aromatic plant materials.
2.7 Pulsed Electric Field Extraction (PEF):17
Pulsed Electric Field Extraction involves applying short bursts of high-voltage electric fields (typically 0.1–80 kV/cm) to plant tissues immersed in a solvent. This causes electroporation—disruption of cell membranes—leading to increased mass transfer of intracellular compounds. PEF is a non-thermal technique ideal for preserving heat-sensitive constituents like antioxidants, vitamins, and pigments. It has been used effectively for juice extraction and improving yields from grape skins, sugar beet, and olives. The major advantages include minimal thermal damage, high efficiency, and rapid processing. However, it requires precise control of electric parameters and may not be cost-effective for small-scale setups due to equipment complexity.
2.8 Subcritical Water Extraction (SWE):18
Subcritical Water Extraction uses water at temperatures between 100°C and 374°C under high pressure (to maintain it in the liquid state) to extract a range of polar and semi-polar compounds. At subcritical conditions, water exhibits decreased dielectric constant, mimicking organic solvents like methanol or ethanol. This allows it to solubilize phenolics, alkaloids, and glycosides efficiently. SWE is considered a green technology and is increasingly used in pharmaceutical and nutraceutical industries. It eliminates the use of harmful organic solvents and provides good selectivity by adjusting temperature. However, SWE systems are capital-intensive, and high temperatures can degrade certain labile compounds if not optimized.
3. Emerging and Advanced Extraction Techniques:
3.1 Natural Deep Eutectic Solvent (NADES)-Based Extraction:19
Natural Deep Eutectic Solvents (NADES) are a novel
class of green solvents formed by mixing natural primary metabolites such as
sugars, amino acids, or organic acids, which form eutectic mixtures with low
melting points. These solvents are biodegradable, non-toxic, and customizable
based on the desired polarity. NADES are being increasingly used for the
extraction of flavonoids, alkaloids, and saponins due to their tunable
solvation properties and ability to dissolve a wide range of phytochemicals.
Compared to conventional solvents, NADES exhibit better selectivity and higher
extraction yields in many cases. Moreover, the use of NADES aligns with
sustainable and safe manufacturing practices. However, challenges like high
viscosity and difficulties in solvent recovery still need to be addressed.
3.2 Pressurized Hot Water Extraction (PHWE):20
Also known as Enhanced Solvent Extraction, Pressurized Hot Water Extraction (PHWE) involves the use of water at elevated temperatures (100–374°C) and high pressures to keep it in a liquid state. PHWE is closely related to Subcritical Water Extraction but focuses more on continuous flow or batch reactors for larger-scale applications. It significantly enhances the extraction of phenolics, polysaccharides, and glycosides from plant matrices without the use of organic solvents. By manipulating temperature and pressure, the polarity of water can be adjusted to target different classes of compounds. This makes PHWE both eco-friendly and versatile. The technique is increasingly adopted in the food, cosmetic, and pharmaceutical industries.
3.3 Flash Extraction:21
Flash Extraction, also known as Instantaneous Controlled Pressure Drop (Dic—Détente Instantanée Contrôlée), is a new thermo-mechanical method that enables ultra-fast extraction of phytoconstituents. It involves subjecting plant material to high-pressure saturated steam for a short time, followed by an abrupt pressure drop. This causes instant auto vaporization of intracellular water, expansion of the material, and cell wall rupture, allowing efficient compound release. The whole process takes only seconds to minutes and is particularly useful for essential oils and antioxidants. Flash Extraction significantly reduces energy consumption and solvent use. It is still under optimization but has high potential for industrial scale-up.
3.4 Ohmic Heating-Assisted Extraction (OHAE):22
Ohmic Heating-Assisted Extraction (OHAE) is an emerging technique that applies electrical current directly through the plant-water mixture, causing rapid and uniform heating via electrical resistance. This enhances cell permeability and facilitates the release of intracellular contents. Unlike conventional heating, ohmic heating ensures minimal thermal degradation and shorter processing times. It is especially suited for aqueous extractions of polysaccharides, proteins, and antioxidants. Though still under evaluation for herbal matrices, it is gaining interest due to its energy efficiency and potential for continuous processing.
3.5 Enzyme Ultrasound Synergistic Extraction (EUSE):23
Enzyme Ultrasound Synergistic Extraction (EUSE) combines enzymatic hydrolysis with ultrasound application to enhance the release of plant metabolites. The enzyme softens or breaks down the cellular matrix, while ultrasound-induced cavitation helps release the compounds rapidly. This combination significantly increases yield and reduces extraction time compared to using either method alone. EUSE has shown excellent results in extracting phenolic acids, flavonoids, and essential oils, especially from complex matrices such as peels, roots, and seeds. The process is considered a potent green alternative and is currently under pilot-scale implementation.
3.6 Ionic Liquid-Based Extraction (ILBE):24
Ionic liquids (ILs) are salts in the liquid state that consist of anions and cations with low melting points, often below 100°C. They are customizable for polarity and are non-volatile, non-flammable, and thermally stable. ILs are increasingly used as solvents for extracting alkaloids, steroids, and essential oils due to their strong solvating power and ability to disrupt plant cell walls. Although ILs are efficient and selective, their high cost and potential environmental toxicity are limiting factors. Ongoing research is focused on developing biodegradable ionic liquids (Bio-ILs) to overcome these issues.
4. Traditional Ayurvedic Method:
Panchavidha Kashaya Kalpana encompasses five fundamental Ayurvedic methods for preparing herbal formulations: Swarasa (expressed juice), Kalka (paste), Kwatha (decoction), Hima (cold infusion) and Phanta (hot infusion). These techniques are designed to extract and deliver the therapeutic properties of herbs effectively, with each method tailored to specific types of plant materials and desired therapeutic outcomes.
4.1 Swarasa25 (expressed juice):
Swarasa involves extracting juice from fresh herbs. The plant material is cleaned, crushed into a paste, and then squeezed through a cloth to obtain the juice. This method is considered highly potent, delivering active constituents in their most unaltered form.
In traditional Ayurvedic pharmaceutics, Swarasa is esteemed as one of the most potent forms of herbal preparation. While it is ideally extracted from fresh plant materials, ancient texts also delineate methods for obtaining Swarasa from dried herbs when fresh counterparts are unavailable. These time-honored techniques ensure the effective extraction of therapeutic constituents, preserving the efficacy of herbal remedies.
1. Soaking Method (Nishpidaṇa):
This method is preferred for dried herbs that are soft or fragile in nature. According to Ayurvedic principles, gentle soaking overnight helps in preserving the subtle, water-soluble active constituents without exposing them to heat, which can degrade delicate phytochemicals like volatile oils or certain glycosides. The softened herb releases these constituents effectively, maintaining their potency and therapeutic efficacy.
2. Decoction Method (Kwathana):
Decoction is chosen when dealing with hard, tough or fibrous dried herbs, where simple soaking fails to extract sufficient active principles. Ayurvedic texts emphasize that boiling with an appropriate ratio of water helps break down the dense plant matrix, enabling the release of heat-stable, water-soluble compounds such as alkaloids, tannins and phenolics. The heat-induced extraction enhances therapeutic strength, making decoctions suitable for chronic ailments where deep tissue penetration and sustained effects are desired, such as in respiratory disorders or digestive imbalances.
3. Putapaka Method:
This traditional technique is specifically applied when extracting juice is difficult due to the herb’s inherent toughness or resistance even in fresh form. The Ayurvedic rationale involves applying controlled heat via a mud-coated bolus, which creates a slow, penetrating thermal effect that softens the herb and activates latent phytoconstituents without causing rapid degradation. This method is considered superior for herbs that require intensified potency and altered pharmacodynamics.
4.2 Kalka26(paste):
Kalka refers to a paste obtained by grinding fresh or dried herbs with minimal water. In Ayurveda, this preparation is considered vital for retaining the full spectrum of phytochemicals, including both water-soluble and fat-soluble constituents. Unlike other methods that may filter out fibrous or insoluble components, Kalka ensures comprehensive utilization of the plant’s active principles.
4.3 Kwatha27(decoction):
In traditional Ayurvedic pharmaceutics, the preparation of Kwatha (decoction) is a fundamental method for extracting water-soluble bioactive compounds from herbs. The ratio of herb to water and the extent of reduction during boiling are critical factors influencing the potency and therapeutic efficacy of the decoction.
Traditional Ratios in Kwatha Preparation.:
1. 1:4 Ratio:
This method is employed for herbs with softer textures, such as leaves and flowers. One part of coarse powdered herb is boiled with four parts of water and reduced to one-fourth of its original volume. This approach allows for quicker extraction of active constituents.
2. 1:8 Ratio:
Suitable for herbs of medium hardness, like soft barks and tubers, this ratio involves boiling one part of herb with eight parts of water and reducing the mixture to one-fourth of its original volume. This method strikes a balance between extraction efficiency and the preservation of heat-sensitive compounds.
3. 1:16 Ratio:
For very hard or fibrous herbs, such as hard barks and root barks, a 1:16 ratio is utilized. The herb is boiled with sixteen parts of water and reduced to one-fourth of the original volume. This extended boiling ensures thorough extraction of active principles from tough plant materials.
4.4 HIMA28:(cold infusion):
Hima is a classical Ayurvedic method of preparing herbal infusion without the application of heat. In this method, powdered herbs are soaked in cold water (1:6), usually for 8–12 hours, and then filtered. This technique is particularly preferred for herbs that contain volatile, heat-labile, or delicate phytochemicals which may degrade upon boiling, such as aromatic compounds or essential oils.
4.5 Phanta29: (Hot Infusion):
Phanta involves pouring freshly boiled hot water over coarsely powdered herbs (1:4), covering the mixture and allowing it to steep (usually 10–15 minutes) before filtering. This method is similar to making herbal tea and is particularly effective for extracting aromatic, mildly active, or moderately heat-stable compounds, especially from soft plant parts like leaves or flowers.
4.6 Arka Kalpana30:
Arka Kalpana is a classical Ayurvedic pharmaceutical technique involving the distillation of herbal materials to obtain a clear, potent liquid known as Arka. Unlike other aqueous preparations such as Swarasa or Kwatha, Arka is distinguished by its long shelf life, rapid absorption, and high therapeutic value. The process begins by soaking the herbal raw material in water typically 6 to 10 times the weight of the drug depending on its hardness and moisture content. After soaking overnight, the material is transferred into a specially constructed distillation apparatus known as Arka Yantra, often made from traditional materials like Jirnasthimrttika (clay mixed with aged bone powder). Heat is then applied (classified into six types from Dhumagni to Bhattagni) to produce steam containing the volatile and water-soluble constituents of the drug. This steam is condensed and collected in a receiver as the final Arka. Depending on the nature of the drug, about 60–70% of the added water is recovered as Arka. The resulting liquid is colorless or pale, aromatic, and highly potent. Arka Kalpana is considered superior in many Ayurvedic texts like Arka Prakasha and is favoured for its palatability, dosage convenience and broad-spectrum therapeutic effects.
These methodologies underscore the ingenuity of ancient Ayurvedic practitioners in ensuring the availability of potent herbal extracts, regardless of the form in which the plant material is obtained. By adapting preparation techniques to the nature of the herb be it fresh or dried Ayurveda maintains the therapeutic integrity of its remedies.