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7
Methods of Extraction
Mohan Kalaskar1, Santosh U. Yele2, Muniappan Ayyanar3, Nilambari Gurav4, Vishal Beldar5,
Sanjay J. Surana
1
Department of Pharmacognosy, R. C. Patel Institute of Pharmaceutical Education and Research, Shirpur, India
2
Department of Pharmacognosy, Poona College of Pharmacy, Bharati Vidyapeeth (Deemed to be) University, Pune, India
3
Department of Botany, A. V. V. M. Sri Pushpam College (Affiliated to Bharathidasan University), Poondi, India
4
Department of Pharmacognosy, P.E.S’s Rajaram and Tarabai Bandekar College of Pharmacy, Ponda, India
5
Department of Pharmacognosy, School of Pharmacy & Technology Management, SVKM’s, Narsee Monjee Institute of Management Studies (NMIMS)
Deemed-to-be-University, Mumbai, India
1
7.1 Introduction
Since ancient times, various cultures worldwide have utilized plant materials to address ailments and maintain
health. Extracting medicinal compounds from plants was
one of the earliest forms of healthcare, and the practice
dates back thousands of years across diverse civilizations,
including those of ancient Egypt, China, India, and Greece.
Historical records reveal the significance of plant extractions in traditional medicine. For instance, in ancient
China, herbal formulations were documented in texts like
the Shen Nong Ben Cao Jing, a foundational work on
medicinal plants. In India, the Ayurvedic system of medicine, dating back over 5000 years, extensively uses plantbased extracts for healing. Similarly, ancient Egyptian
medical papyri, such as the Ebers Papyrus, contained
detailed recipes using plant-based substances for treating
various ailments. The plant extraction methods evolved
with human knowledge and technology. Initially, crude
methods like mashing, soaking, and brewing were used to
extract medicinal properties.
Over time, the field of plant extraction has seen an evolution from rudimentary techniques such as infusion and
decoction to more sophisticated methods like maceration,
percolation, and modern advancements in extraction
technologies.
Moreover, the extraction process allows for the production
of various forms of plant-based medicines, including tinctures, essential oils, extracts, and herbal supplements,
catering to diverse health needs. Advances in extraction
techniques, alongside the integration of technological innovations and analytical tools, have facilitated the efficient
extraction and purification of bioactive compounds, contributing to the development of innovative plant-derived pharmaceuticals and nutraceuticals. Understanding the extraction
of medicinal plants is integral to unraveling their therapeutic
potential and ensuring the sustainable utilization of these
natural resources. This interdisciplinary field continues to
hold promise for unlocking novel therapeutic agents and
expanding our knowledge of the medicinal properties present in the rich biodiversity of the plant kingdom.
Asia, the world’s largest continent and home to 60% of
the global population, boasts a rich diversity of medicinal plants. This vast continent, particularly its tropical
and subtropical regions, has been a reservoir of medicinal and aromatic plants for centuries, as evidenced by
well-documented practices in traditional medicine and
folklore. The utilization of these plants by the native populations presents substantial potential for both social and
economic development. In the global context, Asia stands
out with six mega biodiversity hotspots out of the recognized 18, namely the eastern Himalayas, North Borneo,
Peninsular Malaysia, Sri Lanka, the Philippines, and the
Western Ghats of South India. The countries in the
region possess a significant botanical wealth. China, for
instance, is home to 30 000 species of higher plants, while
Indonesia and India host 20 000 and 17 000 species,
respectively. Myanmar, Malaysia, and Thailand also contribute significantly, with 14 000, 12 000, and 12 000 species, respectively. Highlighting the total number of plant
122 7 Methods of Extraction
Table 7.1 Region-wise distribution of endemic species.
Sr. No Region
1 Southeast Asia 42–50 40
2 East Asia including
China
3 Indian Subcontinent 25 12
4 Southwest Asia 23 7.1
Total species
(thousands)
45 18.65
Endemic species
(thousands)
species and endemics in the region underscores the
immense biodiversity that holds potential for various
fields, including pharmaceuticals, traditional medicine,
and economic development (Table 7.1).
Extraction is a separation process in which the soluble
constituents are removed using solvents. The primary step
involves the rupture of plant cells or the breaking of the cell
wall. Following this, solvents penetrate the plant cell, solubilize the phytochemicals, diffuse out of the plant cell, and
facilitate the extraction of phytochemicals. Various techniques expose plant cells to solvents, allowing for the diffusion or leaching out of phytochemically rich solvents. The
choice of methods depends on the plant part and its tissue,
encompassing maceration, infusion, decoction, percolation, digestion, Soxhlet extraction, superficial extraction,
ultrasound-assisted extraction (UAE), and microwaveassisted extraction (MAE), among others [1]. Furthermore,
the success of extraction relies on selecting an appropriate
solvent to extract the targeted phytochemical. This choice is
determined by the solubility of the phytochemicals; watersoluble compounds and proteins are extracted in buffers or
water, while lipophilic compounds are extracted with
organic solvents. Boiling ethanol is considered a universal
solvent for preliminary extraction [2].
With advancements in medical science and the understanding of molecular biology, numerous attempts have
been made to establish the efficacy of medicinal plant therapies globally. The identification of promising phytochemicals in therapeutically active plants has led to the synthesis
of plant-based medicines. It is estimated that globally, the
market value for all medicinal plant commodities transcends USD 100 billion per year. In present times, despite
the phenomenal growth in the development of synthetic
drugs in pharmaceutical chemistry, almost 75–80% of the
global population use herbal drugs as medicines, mostly in
developing countries, for primary health care because of
their better tolerability with the human body and minor side
effects, and also easier availability. It has been documented
that those natural products are used to develop an estimated
44% of all novel drugs, primarily as lead compounds, to
develop and prepare partially synthetic medicines.
Several factors, including the kind of plant material, solvent type, solvent pH, temperature, and solvent-to-sample
ratio, must be considered when selecting an effective
extraction process. The intended application of the finished products is another factor [3].
7.2 Ideal Properties of Solvent
Numerous considerations are crucial in the selection of
solvents for extraction processes, significantly influencing
the effectiveness of extraction and the quality of the derived
compounds. Essential factors for consideration encompass
the following:
1. Polarity: One of the fundamental factors in solvent selec-
tion is the polarity of the compound to be extracted. It is
essential that the polarity of the chosen solvent corresponds to that of the target compound. For example,
polar compounds can be dissolved in polar solvents like
water, methanol, or ethanol. On the other hand, nonpolar compounds can be best extracted with nonpolar solvents like hexane or chloroform.
2. Selectivity: Solvents should exhibit selectivity in their
capacity to extract the desired compounds effectively.
Consider ethanol, which, due to its versatile nature,
can extract a wide range of phytochemicals from plant
materials, accommodating both polar and nonpolar
compounds.
3. Safety and Toxicity: Safety considerations are para-
mount. The selected solvent should be safe for use and
consumption. Ethanol, frequently employed for extractions, is relatively safe, while solvents with potential
toxicity concerns, such as chloroform, should be used
with caution.
4. Cost and Availability: Practical factors like the cost
and availability of solvents are crucial. Common solvents, such as ethanol and water are economically feasible and readily available, whereas specialized
solvents like ionic liquids might be costlier and less
accessible.
5. Chemical Stability: The solvent should maintain sta-
bility without chemical reactivity with the compounds
to be extracted. Water, known for its chemical stability,
typically avoids reactions with most compounds.
6. Residual Impact: The potential presence of solvent
residues within the extracted material must be minimized to avoid health concerns. Solvents like ethanol
and water pose lower residual risks compared to more
volatile solvents like dichloromethane.
7. Environmental Impact: A growing concern in modern
extraction processes is the environmental impact of
7. 3 Solvents for Extraction 123
the chosen solvents. Environmentally friendly or
“green” solvents, such as water and ethanol, are
increasingly favored options. They offer the dual
advantage of safety and reduced environmental
impact when compared to more toxic solvents like
chloroform or dichloromethane.
7.3 Solvents for Extraction
The selection of an appropriate solvent for the extraction
of medicinal plants is a critical determinant in the extraction process. Several criteria need to be considered while
selecting a solvent, including the type of plant, the exact
portion of the plant that needs to be extracted, and the
makeup of the bioactive compounds present (as depicted
in Table 7.2). The extraction of polar phytochemicals is
often accomplished using polar solvents like water, methanol, and ethanol, whereas the extraction of non-polar secondary metabolites is best attended by non-polar solvents
like hexane, chloroform, and other lipophilic solvents [4].
These solvents are categorized according to their degree of
polarity, with water being extremely polar and n-hexane
being the least (Figure 7.1). A successive extraction process requires the use of solvents arranged in order of
increasing polarity. This sequence typically starts with
n-hexane, the least polar solvent, progressing toward
water, which possesses the highest polarity [5]. It is common practice to use a mixture of solvents to achieve thorough extraction of different phytochemicals. These
solvents can include two low-polarity solvents (n-hexane
and chloroform), two medium-polarity solvents (dichloromethane and n-butanol), and one high-polarity solvent
(water). This stepwise selection of solvents based on their
polarity is crucial during fractionation or successive
Table 7.2 Commonly used solvents for extraction of different
phytochemicals [6].
Sr. No Solvents Phytochemicals
1 Water Anthocyanins, tannins, saponins,
2 Ethanol Tannins, terpenoids, polyphenols,
3 Methanol Anthocyanins, terpenoids,
4 Chloroform Terpenoids and flavonoids
5 Dichloromethanol Terpenoids
Diethyl Ether Alkaloids and terpenoids
6
7 Acetone Flavonoids
and terpenoids
flavonols, and alkaloids
saponins, tannins, polyphenols,
and flavones
POLARITY OF SOLVENTS
Highly Polar
-
Acetic Acid
-
Ethylene glycol
-
Methanol
-
Isopropanol
pyridine
-
-
Nitromethane
-
Diethylamine
-
Aniline
-
Dimethyl sulfoxide
-
Ethyl acetate
-
Dioxane
-
Dichloroethane
-
Tetrahydro furan
-
Dichloromethane
-
Chloroform
-
Diethyl ether
Toluene
-
Carbon tetrachloride
-
Petroleum ether
-
Hexane
Highly Non-Polar
Figure 7.1 Descending polarities of different solvents used in
the extraction of plants. Source: Kalaskar MG.
extraction processes. Employing a range of solvents with
varying polarities allows for a more comprehensive extraction of diverse phytochemical compounds, ensuring a
broader spectrum of bioactive components is captured
from the plant material.
In the extraction of phytochemicals, no single solvent is
universally ideal, as each solvent possesses a distinct polarity
that confers specific advantages and disadvantages. The
selection of solvents for extraction is based on their unique
characteristics [6–8]. Several widely used solvents in this process are detailed below.
1. Water: Known for its high polarity, is a widely used sol-
vent for extracting a broad spectrum of polar compounds. Its low cost, non-flammable and non-poisonous
nature, high polarity, and capacity to dissolve a wide
range of compounds are among its advantages.
However, water can cause hydrolysis and promote the
growth of bacteria and mold, and it often needs a considerable quantum of heat to concentrate extracts.
2. Alcohol: Also polar and miscible with water, alcohol is
effective in extracting polar secondary metabolites. Its
benefits include not being poisonous at low concentrations, self-preserving at concentrations above 20%, and
requiring little heat to concentrate the extract.
However, alcohol fails to dissolve fats, gums, and
waxes, and poses flammability and volatility risks.
124 7 Methods of Extraction
3. Chloroform: It is a nonpolar solvent that is useful for
extracting substances, such as oils, lipids, terpenoids,
and flavonoids. Its benefits include being colorless,
having a sweet smell, solubility in alcohols, and efficient absorption and metabolism in the body. However,
it presents sedative and carcinogenic properties.
4. Ether: Another nonpolar solvent, ether aids in the
extraction of compounds like alkaloids, terpenoids,
coumarins, and fatty acids. It boasts advantages such
as miscibility with water, a low boiling point, tastelessness, and stability without reactions with acids, bases,
or metals. On the downside, ether is highly volatile
and flammable.
5. Ionic liquid (green solvent): This unique solvent stands
out for its high polarity and extreme heat stability, even
remaining in a liquid state at very high temperatures,
up to 3000 °C. It showcases high miscibility with water
and other solvents, ideal for extracting polar compounds. Its perks include excellent microwave transmission, making it suitable for MAE, non-flammability,
and applicability for liquid-liquid extraction due to its
highly polar nature.
2. Nature of solvent: Maceration is a good technique if
the extraction solvent is water; however, Soxhlet
extraction and percolation are better suited for volatile
solvents.
3. Cost of the drug: The cost of extracting a drug influences
the selection of extraction methods. Less expensive
drugs often utilize more cost-effective extraction techniques like maceration, which may be less efficient. On
the contrary, costly drugs require more thorough extraction processes, such as soxhlation or modern methods
like MAE. These advanced methods, though more
expensive, are preferred for their effectiveness in extracting higher-value compounds, ensuring a more comprehensive yield from the costly drug materials.
4. Nature of raw material: Depending on the type of raw
material, the extraction process selected will vary. For
unorganized crude drugs like gums or mucilage, maceration proves to be the most suitable extraction
method. In the case of organized raw materials, methods such as percolation, Soxhlet extraction, or other
modern techniques are considered more appropriate
for efficient extraction processes.
7.4 Factor Affecting Extraction Methods
1. Nature of phytochemicals: Phytochemicals that are
heat-stable are typically extracted through methods
such as Soxhlet extraction or MAE. In contrast, for
thermolabile phytochemicals, extraction methods like
maceration, percolation, or UAE are more suitable.
Washing out
7.5 Mechanism of Extraction
The plant material must be comminuted into fine to coarse
powder based on the type of extraction process and then
steeped in the extraction solvent. When the herbal material
comes into contact with the plant material, the extraction
process begins with penetration, followed by diffusion, and
ends with diffusion (Figure 7.2) [9].
Penetration
Solubilization
Diffusion
Figure 7.2 Schematic presentation of solvent and phytochemical interactions during the extraction process. Source: Kalaskar MG.
7. 6 Methods of Extraction 125
1. Penetration: The solvent when comes in contact with
the plant material, it starts to penetrate the plant material through methods like soaking, maceration, or percolation. This allows the solvent to penetrate the plant
cell walls and reach the phytochemicals.
2. Solubilization: Once the solvent reaches the plant
cells, it interacts with the phytochemicals. The solvent
dissolves the phytochemicals, creating a solution containing a mixture of compounds extracted from the
plant material. Different compounds may require varying lengths of time or different solvent properties for
effective solubilization.
3. Diffusion: The dissolved phytochemicals move from
regions of higher concentration (inside the plant
cells) to regions of lower concentration (the surrounding solvent). This is driven by diffusion, aiming to achieve equilibrium between the concentration
of compounds inside and outside the plant cells.
Thus, the extraction occurs.
4. The conventional method of extraction relies on the
prominent mechanisms of penetration, solubilization,
and diffusion. In contrast, the modern method of
extraction operates through the mechanism of bursting and washing out.
Modern extraction methods utilize various energy
sources, such as microwaves, ultrasound, and electric currents. These methods generate vibrations or pressure on
the plant cell walls, leading to the bursting of cells.
Consequently, this process doesn’t rely on a concentrationdependent diffusion mechanism. Instead, it exposes all
phytochemicals present within the plant cells directly to
the extraction solvent. The phytochemicals are then
washed out based on their solubility. This mechanism significantly enhances efficiency as it operates on solubility
principles, ensuring that all phytochemicals present in the
plant material are efficiently extracted, making it a more
effective method compared to conventional extraction.
7.6 Methods of Extraction
Extraction is the process of separating a substance from a
mixture. There are many different extraction methods,
each with its own advantages and disadvantages. The
choice of extraction method depends on the specific substances being extracted and the desired purity of the final
product.
The conventional method of extraction, also known as
classical extraction, refers to a set of well-established techniques used to isolate and concentrate desired components
from a mixture. These methods typically involve using a
solvent to dissolve the target compound(s) from the source
material, followed by separation of the solvent and the
enriched extract. These methods require more time and
solvents for complete extraction. On the contrary, modern
extraction methods are often more efficient and less timeconsuming than traditional methods. They also tend to be
more environmentally friendly, as they use less solvent and
produce less waste.
The conventional extraction methods include the
following:
1. Decoction
2. Maceration
3. Percolation
4. Soxhlet extraction
5. Extraction of essential oil techniques
The modern methods of extraction methods comprise of
the following:
1. Phytonics
2. Pressurized liquid extraction/accelerated solvent
extraction
3. Pulse electric extraction
4. Ultrasound-assisted extraction (UAE)
5. Microwave-assisted extraction
6. Supercritical fluid extraction (SFE)
7.6.1 Decoction
This process involves boiling the plant material in water for
15–60 minutes to extract substances. The solvent-to-crude
drug ratio is typically 4 : 1 or 16 : 1. It is employed to extract
plant material that is heat-stable and water-soluble.
During decoction, plant material is boiled in water for
15–60 minutes [3]. The duration of boiling will depend on
the nature of plant tissues and the phytochemicals being
extracted. Ordinarily, delicate plant parts such as leaves,
roots, flowers, and tender stems are boiled for 15 minutes.
For instance, phenols and flavonoids have been extracted
using decoction and infusion from fruits, rhizomes, and
leaves at 100 °C [10, 11]. Instead, hard plant parts such as
branches and tree barks can be subjected to boiling for an
hour. After boiling, the mixture is cooled and then strained,
it is not the ideal method for thermolabile compounds.
Powdered crude drug +
solvent (1:6; 1:4)
Boiled with water for
15–60 min
Filtered & Conc. extract
126 7 Methods of Extraction
Powdered crude drug +
solvent (1:6; 1:10)
Kept for 7 days with
occasional shaking
7.6.2 Maceration
The general process of maceration on a small scale involves
placing moderately coarse powder in a closed vessel with a
selected solvent for extraction. This system is left to stand
for two to seven days, occasionally shaken. The extract is
then strained off, and the plant residue is pressed to
recover the maximum extract, followed by filtration of the
extract to remove solid impurities. Preferably, maceration
is carried out in a stoppered container to minimize solvent
loss through evaporation [12]. The extract is frequently
concentrated using vacuum evaporation. Choosing an
appropriate solvent in maceration is crucial as it determines the classes of phytochemicals salvaged from the
samples and can enable the extraction of thermolabile
phytochemicals.
The extended extraction time is required to ensure the
solvent will fully penetrate the plant cell wall and dissolve
the components inside the cells, followed by diffusion
across the cell membrane based on the concentration gradient. As the extraction process is mostly static, occasional shaking assists in breaking the boundary wall of
the solute and aids in active diffusion, bringing a new solvent to the surface of the plant cell particle surface to
facilitate efficient extraction.
However, this procedure has the underlying disadvantage of low efficiency and long duration for extraction [3].
Yet, under optimized conditions, this technique has shown
significant efficiency, yielding high phenolic compounds
and anthocyanins from chokeberry [13]. Comparative
studies have revealed that maceration techniques generally
yield less than modern extraction methods [14].
7.6.2.1 Modified Macerations
1. Kinetic Maceration: It is a dynamic extraction tech-
nique used to extract bioactive compounds from plants.
This involves a controlled process where the plant matter is subjected to mechanical forces, such as agitation or
stirring, along with the extraction solvent. This continuous movement helps in enhancing the extraction process
by increasing the plant surface area exposed to the solvent, thereby improving the extraction efficiency. In
addition, it also reduces both extraction time and solvent
usage while achieving higher yields.
2. Digestion Maceration: It is a method for extracting
compounds from plant material by applying gentle,
controlled heat during the maceration process. This
technique involves immersing the plant material in a
Filtered & Conc. extract
solvent of choice and then heating the solvent-plant
mixture at a controlled temperature for a specific
period of time. The application of controlled heat aids
in accelerating the extraction process by increasing the
solubility of compounds in the solvent. Additionally,
digestion maceration can offer advantages over other
methods, such as the ability to extract heat-sensitive
compounds or target-specific components based on
their varying heat solubilities.
A study revealed that the combination of temperature
and duration of kinetic maceration-digestion yielded
higher levels of both extract yield and tannin content from
areca seeds, demonstrating its superiority over conventional maceration [15].
7.6.3 Percolation
The literal meaning of percolation is passing through. In
this extraction process, the solvent is passed through the
column of the drug, which is packed in a special apparatus
called a percolator. The process involved critical packing of
a drug in the percolator. The packing involved carefully
bedding of moistened drug in the percolator over a previously moistened glass wool or other suitable material,
ensuring loose and uniform packing. After this step, a filter
paper is placed on top of the drug bed, and washed pebble
stones are then placed on the filter paper to ensure that the
top layer of the drug remains undisturbed when the solvent is added for extraction (maceration) and controlled
flow of solvent through it (Figure 7.3).
Lid
Filter paper with
washed pebbles
Drug column
Percolator
Filer medium
(usually glass wool)
Flow regulating
valve
Figure 7.3 Packing of the drug in the typical conical
percolator. Source: Kalaskar MG.
7. 6 Methods of Extraction 127
The process of percolation can be divided into three steps
as follows:
1. Imbibition
2. Maceration
3. Percolation
7.6.3.1 Imbibition
The organized crude drug can be categorized into soft tissue
and hard tissue types. Soft tissue plant material exhibits a
tendency to swell upon contact with solvents. While certain
materials, such as ginger, can be directly packed into the
percolator in a dry state, this approach may pose challenges
for other drugs. The swelling caused by soft tissue plant
material can restrict or even impede solvent flow, thereby
significantly hindering the extraction process. Packing dry
powder can cause small particles to go down the column,
settling at the bottom and significantly decreasing porosity,
which could block the column completely. These fine particles may even be washed out of the percolator altogether.
Uneven packing further complicates the extraction process
by allowing more solvent to pass through channels with
lower resistance, resulting in inefficient extraction. To overcome these challenges, it is advised to uniformly wet the
raw material with the solvent in a closed tank for four hours
as a first step. Imbibition is the process by which the crude
drug swells to its maximum extent, facilitating optimal solvent penetration and efficient extraction.
7.6.3.2 Maceration
After the packing of imbibed plant material, the percolator is
filled with solvent, and as the solvent starts dripping through
the tap, the tap is shut. A necessary amount of solvent is then
added to uphold an ample layer above the drug column, and
the mixture is left undisturbed for a duration of 24 hours.
This process of steeping a drug with solvent is known as maceration. This is a crucial step in percolation extraction, as the
maximum extraction occurs through the mechanisms of
penetration, solubilization, and diffusion.
7.6.3.3 Percolation
After the maceration, the outlet of the percolator is opened to
percolate macerated solvent at a controlled rate with continuous addition of fresh solvent. The quantity of percolate gathered varies based on the characteristics of the end product. In
general, about 75% of the volume of the finished product is
collected [3, 16].
There are two types of percolations used for the extraction of phytochemicals from medicinal herbs. That includes
cold percolation and hot percolation.
1. Cold Percolation: The cold percolation is simplest
method of percolation. The comminated plant material is packed into a percolator as described earlier.
Fresh solvent is then added and allowed to macerate
for a sufficient period, allowing the plant active chemicals to equilibrate with the solvent. Subsequently, the
solvent is permitted to percolate slowly from the outlet, ensuring a controlled rate to maximize extraction
efficiency. While this method is straightforward, it is
not the most efficient due to the slow mass transfer
rate, leading to a prolonged time required to reach
equilibrium.
To address the limitations, multiple percolations can be
employed. This technique involves repeated percolation of
fresh solvent through the equilibrated plant material, typically four to five times, until the plant material is exhausted
for active phytochemicals. All percolates are then pooled and
concentrated. Although this method achieves a more complete extraction, it requires a significantly higher solvent volume compared to simple percolation.
To overcome the issue of incomplete extraction in a single percolation step, a series of connected percolators can
be employed. This approach, particularly suited when multiple percolations are necessary for complete extraction,
utilizes four or more percolators arranged sequentially. The
plant material to be extracted is evenly distributed amongst
all percolators. The outflow from the first percolator serves
as the inflow for the second, and so on, with the final percolator’s outflow collected as the enriched extract. The
extraction process commences with the addition of fresh
solvent to the first percolator. Following an equilibration
period, the solvent is transferred to the second percolator.
At each stage, the solvent is allowed sufficient time to reach
equilibrium with the active principles present in the plant
material. In the final percolator, the solvent achieves equilibrium with the plant phytochemicals four times over.
Conversely, the plant material in the first percolator
remains in contact with fresh solvent for four consecutive
cycles. This counter-current flow ensures exhaustive
extraction. As the first percolator becomes depleted of
active principles, it can be disconnected from the series and
replaced with a fresh percolator containing new plant
material. By implementing this rotation system, each percolator’s solvent interacts with the solid material three
times, becoming fully saturated with the target compounds.
The concentrated extract subsequently undergoes solvent
recovery and concentration. This method only necessitates
the concentration of one enriched extract (Figure 7.4). This
significantly reduces energy consumption and improves
overall process efficiency, lending itself well to continuous
operation [17].
128 7 Methods of Extraction
Solvent
Reservoir
Figure 7.4 Schematic presentation of multiple percolation. Source: Kalaskar MG.
Percolator
1
Percolator
2
Flow of solvent
Percolator
3
Percolator
4
Extract
Receiver
2. Hot Percolation: In the extraction processes, the rela-
tionship between solvent temperature and the solubility of active compounds is a critical consideration.
Elevating the solvent temperature offers a significant
advantage: it amplifies the solubility of the active principle. This heightened solubility creates a more pronounced concentration gradient, consequently
bolstering the shift of the phytochemicals from the
plant material into the extracting vehicle, provided the
phytochemicals are thermostable. This can be accomplished by the integration of a heat exchanger positioned connecting the circulation pump and the inlet
of the percolator. This configuration optimizes the process by incessantly channeling the extract through a
tubular heat exchanger, a conduit warmed by the
introduction of steam. This elevated temperature,
meticulously regulated by a steam solenoid valve, is
overseen by a temperature indicator controller, ensuring precise control over the percolator’s extract temperature. This setup can be used in either a single
percolator or in a series of percolators as required.
Percolation remains a prevalent method in industrial
extraction, employing tall cylindrical towers resembling
percolators. However, loading the drug into these cylindrical percolators demands significant labor and time. To
streamline this process, perforated baskets have been introduced. These baskets allow for the convenient loading of
the material to be extracted outside the extractor. Using a
chain pulley block, these loaded baskets can be inserted
into the extractor, simplifying the extraction process. Postextraction, they can be lifted out from the extractor for discharging the residual material. In certain extractor designs,
an electrical hoist facilitates both the loading of materials
and the discharge of residual matter (marc). This implementation significantly reduces labor requirements while
enhancing the speed and efficiency of operations [17].
7.6.4 Soxhlation (Hot Continuous Percolation)
This extraction method operates on percolation principles
and is commonly known as the Soxhlet extraction method,
developed by von Soxhlet in 1879. The Soxhlet extraction
system comprises an extractor, referred to as the Soxhlet
apparatus, which includes a cellulose cartridge (also known
as a thimble) where plant material is placed. Moreover,
there is a round-bottom flask placed beneath the extractor
and a reflux condenser positioned over the collection flask.
The typical apparatus is depicted in the Figure 7.5.
It is based on the same principle of percolation, i.e. imbibition, maceration, and percolation process. The plant
material is imbibed with a sufficient quantity of solvent
and filled in the Soxhlet apparatus, which has a specific
arrangement of perforation, one for solvent vapor open
from the side bottom and open above the level of the thimble (drug packing), and another perforation from the bottom of Soxhlet, which extended as siphon from the side of
Soxhlet and opens below the opening of the side arm.
Cooling water out
Cooling water in
Condenser
Side arm/vapor
path
Siphon tube
Thimble
RBF with solvent
Heat source
Flow of Solvent
Figure 7.5 Schematic diagram of soxhlation (hot continuous
percolation). Source: Kalaskar MG.
Flow of extract
7. 6 Methods of Extraction 129
After placing the sample in the extractor and adding the
solvent to the collection flask, the heat is activated. As the
temperature rises, the solvent evaporates and passes
through the reflux condenser, returning to the extractor in
liquid form. The solvent saturates the sample, facilitating
the extraction of the desired compounds. Subsequently, the
extract is transferred back to the collection flask through a
siphon. Soxhlet extraction offers several advantages, such
as simplicity, low capital cost, and efficient solvent reutilization for extraction purposes. However, it does come with
limitations, notably the inability to agitate and its unsuitability for thermolabile solvents [18, 19]. To overcome these
drawbacks and enhance efficiency while reducing extraction time, modifications have been introduced to the conventional Soxhlet method. These modifications encompass
operating the method under high pressure (1000–1500 psi),
combining it with ultrasound and microwave techniques,
and automating the extraction assembly [18].
7.6.5 Extraction of Essential Oil Techniques
Different techniques are commonly employed to extract
volatile compounds, such as essential oils, which are not
soluble in water, from a variety of aromatic and medicinal
plants. It has wide applications for the extraction of essential oils from plants [2, 19]. These methods can be categorized as follows:
1. Distillation–hydro distillation, steam distillation
2. Maceration–enfleurage and digestion
3. Physical method–expression and eculle
7.6.5.1 Distillation
The distillation process involves heating the material with
solvent, converting into a vapor phase, followed by condensation in the receiver to obtain a product. In the case of
essential oil extraction, the aromatic plant material is
packed in a vessel with water or on a perforated plate, and
live steam is passed through it, which later is connected to
the condenser and receiver. Exposing aromatic plants to
hot water or steam releases the essential oil from the essential oil glands of the plant tissue. The mix of water and
essential oil vapor condenses through indirect cooling with
water in a condenser. The distillate is sent to a separator,
where the oil separates from the distilled water.
Hydrodiffusion stands as the primary mechanism governing the distillation process, which entails the movement of essential oils and hot water through plant
membranes. As such, plant cell membranes are nearly
impermeable to volatile oils. In hydrodiffusion, as water
boils, some volatile oils solubilize into the water within the
glands. This mixture of oil and water then penetrates the
swollen membranes through osmosis, ultimately reaching
the outer surface. Here, the oil undergoes vaporization
upon exposure to passing steam. It is noteworthy that the
rate of essential oil vaporization remains unaffected by the
volatility of the oil components; rather, it depends upon
their solubility in water. Consequently, constituents with
higher boiling points yet greater water solubility within the
plant tissue distill before those with lower boiling points
but lesser water solubility. Given the relatively slow rates of
hydrodiffusion, the distillation process for uncomminuted
material necessitates a longer duration compared to comminated material (Figure 7.6) [20].
7.6.5.1.1 Disadvantages of Hydro Distillation
Incomplete extraction poses the primary drawback of
hydro distillation. Certain compounds, like esters, undergo
partial hydrolysis, and sensitive substances, such as aldehydes, tend to polymerize during this process.
Hydro distillation necessitates a large number of distillation vessels, large space, and increased fuel consumption. Its
execution requires significant expertise and understanding
of the technique.
The method is not economically feasible for high-boiling
and water-soluble oil components since they cannot be
completely evaporated and need additional steam.
I II III
f
c
d
e
Steam
generator
d
e
f
c
b
a’
d
e
f
c
b
a
Heat Source
Figure 7.6 Distillation process I) hydrodistillation, II) hydrosteam distillation, III) steam distillation, where a: water; b:
perforated plate; c: plant material; d: condenser; e: collecting bottle; f: water circulating tube; a’: steam. Source: Kalaskar MG.
Heat Source
b
a
130 7 Methods of Extraction
7.6.5.1.2 Hydro Steam Distillation
This method resembles hydrodistillation but involves specific
adjustments. It includes setting up a perforated lattice to lift
the plant material above the water level. Connecting a cohobation tube enables the recirculation of condensed water
throughout the distillation process, guaranteeing a sufficient
water supply in the distillation vessel. Moreover, this technique aids in controlling the loss of solubilized oxygenated
components in the condensed water. The reused condensed
water becomes saturated with dissolved constituents, facilitating the dissolution of more oil (Figure 7.6) [16, 17].
7.6.5.1.3 Advantages of Hydro and Steam Distillation over Hydro Distillation
1. Enhanced essential oil production.
2. Reduced likelihood of successful hydrolysis and polym-
erization processes with volatile oil components.
3. Proper management of the refluxing process mini-
mizes the loss of polar compounds.
4. Steam and water distillation result in more consistent
oil quality.
5. Steam and water distillation is a quicker and more
energy-efficient method compared to water distillation.
7.6.5.1.4 Disadvantages of Hydro and Steam Distillation over Water Distillation
Oils that have a high boiling point need more steam to turn
into vapor during distillation. This means the process takes
longer.
When distilling, the plant material gets wet because the
steam needs to turn the water in the material into vapor
before it can condense higher up in the still.
To stop the lower plant material from getting soaked, a
baffle is used. It controls the boiling of water, preventing it
from vigorously contacting the plant material directly.
c) The preferred method for large-scale oil produc-
tion, when compared with the other two methods.
2. Disadvantage: Significantly greater capital invest-
ment is required to initiate this operation compared
to the other two processes.
7.6.5.2 Expression
Extraction of essential oil from citrus fruit is specially done
by expression technique. It is ideal for aromatic plants,
which contain a higher amount of essential oil cells in the
epidermis of the plant. There are two methods that are
sponge technique and equaling. In the sponge method, the
citrus peels are either blended into the sponge or pushed
against a hard object that is placed underneath a huge natural sponge. Later, the oil absorbed by the sponge was separated by pressing against a hard object or some other
container. The oil extracted by this method has a natural
aroma than other methods [16, 17].
The second approach, called equaling, involves using a
shallow bowl made of copper or brass with a hollow central
tube. The equaling tool looks like a shallow funnel. The
bowl contains brass points with blunt ends. The citrus fruit
is rolled across these points by hand or by an automated
machine with pressure until all the oil glands have burst.
The oil and aqueous cell contents flow down the hollow
tube into a container (Figure 7.7). The oil is extracted from
the mixture using decantation and subsequently isolated
from the juice.
7.6.5.3 Ecuelle
In the ecuelle process, citrus fruits are introduced from a
hopper into the abrasive shell of the apparatus. A deliberate
and gradual rotation of the fruits occurs against the abrasive
Fresh citrus peels
7.6.5.1.5 Direct Steam Distillation
It is the most commonly used method for producing essential
oils in large quantities. It is a common practice in the flavor
and fragrance supply industry. This process involves heating
the plant material via steam distillation, which is produced
by a satellite steam generator located outside the still, commonly known as a boiler. Unlike water and hydro steam distillation methods, steam distillation allows for precise control
of the steam amount, limits the heating of plant material to
100 °C, and prevents thermal deterioration (Figure 7.6).
1. Advantages:
a) Steam can be controlled as per need.
b) The components of oil do not undergo heat
degradation.
Volatile oil
Figure 7.7 Expression technique of extraction of volatile
oil. Source: Kalaskar MG.