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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5217_Библиотеки_им_академика_М_И_Перельмана.pdf
Chapter 2 Methods of obtaining drugs from medicinal and aromatic plants 63
2.3.2.1 Comminution and homogenization
Comminution and homogenization are important steps in preparing raw plant material for extraction and subsequent comprehensive analyses.
The particle size of plant materials affects extraction efficiency, making the fragmentation of materials a critical pretreatment process. When particle size is reduced,
there is greater interaction between the samples and the extraction solvents at the
surface level. Powdered samples, with their smaller and more uniform particle size,
enhance surface contact with the solvents, whereas ground samples result in larger,
irregularly sized particles. For extraction to be effective and efficient, the solvent
must interact with the target analytes as much as possible [48]. Comminution and
grinding increase the rate at which the solvent penetrates the solid material. However, in some cases, very fine grinding and pulverization may not be suitable. Extremely fine grinding can cause the solids to compact and form a mass during extraction, obstructing the free flow of the solvent. Additionally, in materials with a cellular
structure, grinding may lead to cell rupture, which can result in the extraction of unwanted components [55, 56].
An appropriate comminution technique can be selected based on the texture and
hardness of the plant material.
The following points should be considered during the comminution and grinding
of materials:
1. Essential oils are sensitive to temperature, so any increase in temperature should
be avoided when working with raw materials containing these compounds. To
prevent the loss of essential oils, the material should be ground in small quan-
tities.
2. Roots, tough stems, fruits, and seeds are initially chopped by hand or machine
and then processed into smaller pieces using different mechanical grinding mills
3. Manual cutting is a simple and equipment-free method for comminution. How-
ever, since it produces pieces of varying sizes, sieving the cut material is recom-
mended to ensure uniformity [50].
The next step after the comminution process is the homogenization of the material.
The mixing process is essential both during the initial preparation of the material and
in subsequent steps to ensure the homogeneity of the material [48]. For this purpose,
various manual or mechanical homogenizers can be used. Sample homogenization
can also be accomplished via enzymatic lysis (often hydrolysis), freezing in a way that
ruptures the cellular wall or membrane, high-energy ultrasound vibrations, and other
nonmechanical physicochemical processes. One important point to consider during
the homogenization process is to prevent thermal degradation of the material due to
excessive heating [50].
64 İrem Yıldız Özbaş, Severina Pacifico, and Emre Özbaş
2.3.3 Extraction
Parts such as the roots, stems, leaves, flowers, seeds, or even the entire plant can be
used fresh or dried for therapeutic purposes. Medicinal plants contain numerous active compounds that can exhibit different physiological effects in various parts of the
plant. To identify and isolate these active compounds, they must first be separated
from the plant through the extraction procedure [8].
The extraction of plant materials is the most critical step before the isolation and
purification of plant components. Plant constituents naturally exist in a complex matrix, and their physical and chemical characteristics vary significantly. The properties
of the target molecule, believed to be responsible for the pharmacological activity or
considered a drug candidate, must be well understood. To obtain it in pure form, it
must be carefully separated from the rest of the plant. This is only achievable through
an appropriate extraction method and optimized extraction parameters [57]. Extraction
involves isolating the medicinally active components of plants using selective solvents
and standardized methods. The distribution of a compound between two immiscible
phases, which permits their subsequent separation and recovery of the extracted compound, is the fundamental principle of extraction [56]. Utilizing variations in the mixture of components’ physical or chemical characteristics is the foundation of extraction
techniques. Particle or molecular size and shape, density, solubility, and electrostatic
charge are some of the more often used characteristics in separation procedures. Some
operations include more than one of these qualities. Nonetheless, the majority of the
processes are physical in nature [55]. The extraction processes of secondary metabolites
in plants are related to the solubility differences of compounds in a solvent mixture.
During this process, the solvents penetrate the plant material and dissolve components
with similar polarity, thereby separating them from others [58]. Separating the soluble
plant metabolites from the insoluble cellular marc (residue) is the aim of all extraction
processes. Crude extracts obtained through these methods typically consist of a complex
mixture of various plant metabolites, including alkaloids, glycosides, phenolics, terpenoids, and flavonoids [48].
The extraction step is one of the initial stages in obtaining an active compound
from plant material. Further separation, identification, and characterization of bioactive compounds can only be achieved after performing an appropriate extraction process. Therefore, the extraction process and techniques can significantly influence the
outcomes. In the process of identifying and isolating an active compound from a
plant, several critical steps must be carefully considered, such as accurately identifying the plant, accounting for potential transformations throughout the process of pretreatment and extracting the material, followed by the elimination of known compounds at the initial stage of fractionation [33].
The efficiency and outcomes of the extraction process are influenced by numerous factors. The most significant among these are the matrix properties of the plant
material in which the components are embedded, the type of solvent used, tempera-
Matrix properties of the material
Pre-treatment of the material
Type of solvent
Mixing speed and mixer type
Temperature
Pressure
Time
1
2
3
4
5
6
7
Figure 2.9: The factors affecting extraction efficiency.
ture, pressure, and time (Figure 2.9) [8, 59].
Plant metabolites are typically found as complex mixtures containing numerous substances with varying degrees of polarity and hydrophobicity. The main categories of
these substances in plant materials include low-polar compounds (e.g., waxes, terpenoids), semipolar compounds (e.g., lipids, phenolic compounds, low-polar alkaloids),
and high-polar compounds (e.g., polar glycosides, polar alkaloids, saccharides, peptides, and proteins) [50]. Based on the differing polarities and structural characteristics of
metabolites, one of the most crucial parameters in the extraction process is the choice
of solvent. Solvent selection should consider the extraction method, the part of the
plant to be used, the target active metabolites, and the intended use of the obtained
extract. The polarity of the solvent is also an important criterion to reach the target
components in the extraction process. A wide range of solvents is available, from low
polarity to high polarity, where polar solvents are used for polar components, and nonpolar solvents are used for components with lower polarity. Generally the selectivity of
extraction can be enhanced by using solvent mixtures instead of a single solvent.
The solvents commonly used in extraction processes and their polarities are shown in
Figure 2.10 [60]. Beyond polarity, many other factors influence solvent selection. The
most significant of these include the solvent’s safety, selectivity, toxicity, and environmental impact [33, 61]. Besides the type of solvent, other parameters influencing extraction efficiency include the ratio of the sample to the solvent, the temperature of the
extraction environment, and the physicochemical features of the material [62].
To prevent oxidative damage in plant materials and to preserve the biological activities and other properties of the components extracted from plants, extraction parameters such as pH, temperature, and time must be carefully adjusted [51]. Tempera-
Chapter 2 Methods of obtaining drugs from medicinal and aromatic plants 65
Figure 2.10: Solvent polarity and eluotropic strength (ɛ°).
66 İrem Yıldız Özbaş, Severina Pacifico, and Emre Özbaş
Chapter 2 Methods of obtaining drugs from medicinal and aromatic plants 67
ture is a crucial factor in the extraction of solid materials. High temperatures enhance
the solubility of components in solvents, allowing for higher extraction yields. Raising
the temperature decreases the viscosity and surface tension of the solvent, resulting
in improved diffusion efficiency. However, elevated temperatures may also lead to
solvent losses, the extraction of some unwanted components, and most importantly,
damage to certain sensitive compounds in the plant material. Therefore, the proper
temperature should be selected based on the characteristics of the plant material
being processed [51, 55].
Although it is possible to extract all components from medicinal and aromatic
plants using various extraction methods, it is not always feasible to determine the effect of each individual component in an extract. Some components may be present in
quantities too small to detect their activity, while others in the extract may mask the
effects of certain compounds. Pre-fractionation and the application of novel extraction techniques are two strategies that can be used to accomplish this. It has been
demonstrated that employing these strategies improves the quality of hit leads for
medication development [2].
Numerous factors related to the plant itself also influence the extractability of its
components. The properties of the matrix in which the components are embedded
(which vary depending on the plant’s botanical and anatomical origin and the part
used) can become the most critical criteria in selecting the extraction method [51].
The growing interest in natural bioactive compounds has increased the demand
for more advanced extraction methods. At the small manufacturing enterprise (SME) or
small research setting levels, traditional techniques like maceration and Soxhlet extraction are frequently employed. These traditional extraction techniques, which are widely
used and rely on simple equipment, require long processing times, high energy consumption, and large amounts of solvents. Due to these disadvantages, traditional methods have been increasingly replaced by modern and innovative techniques. Significant
progress has been achieved in the processing of medicinal plants, including the use of
contemporary extraction techniques like supercritical fluid extraction (SFE), ultrasound-assisted extraction (UAE), and microwave-assisted extraction (MAE), which are
intended to boost output at a reduced cost. These advanced methods achieve significantly higher yields in the recovery of bioactive compounds while greatly reducing the
need for large quantities of raw materials Additionally, changes to the techniques are
always being created. With so many different approaches available, choosing the best
extraction technique requires careful consideration. The main methods used for the extraction of plant samples are summarized in Figure 2.11 [48, 62].
2.3.3.1 Conventional extraction techniques
Several traditional extraction methods can be used to extract bioactive chemicals
from plant sources. The majority of these methods rely on the extraction capabilities
CONVENTIONAL EXTRACTION TECHNIQUES
Maceration
Infusion
Decoction
Percolation
Soxhlet extraction
Distillation
ADVANCED EXTRACTION TECHNIQUES
Ultrasound-assisted extraction (UAE)
Pulsed-electric field extraction (PEF)
Microwave assisted extraction (MAE)
Supercritical fluid extraction (SFE)
Pressurized liquid extraction (PLE)
Enzyme assisted extraction (EAE)
Solid-phase micro extraction (SPME)
Figure 2.11: Conventional and advanced extraction methods.
68 İrem Yıldız Özbaş, Severina Pacifico, and Emre Özbaş
of the various solvents being applied, as well as the use of heat and/or mixing. In all
these methods, the extraction process is performed by treating the material with a
solvent at high thermal condition and/or with agitation [63].
Maceration, infusion, decoction, percolation, and Soxhlet extraction are traditional extraction methods applied to medicinal and aromatic plants. The most significant disadvantages of these methods are the long processing times and the excessive
use of organic solvents. Decoction and hydrodistillation methods, on the other hand,
use water as the solvent. Traditional extraction methods are based on solid-liquid
(matrix-solvent) extraction, where phytochemical components are extracted from
their matrix using various solvents depending on their solubility properties. In these
methods, the solvents penetrate the solid plant materials and dissolve the compounds
with similar polarity. Applying a solvent with suitable polarity in combination with a
compatible extraction method is critically important, depending on the target compounds [64]. The most commonly used solvents, based on the type and polarity of the
compounds intended for extraction from plants, are shown in Figure 2.12 [64, 65].
Compared to modern techniques, conventional extraction methods have two main
disadvantages: they require higher temperatures and take longer, which can lead to the
degradation of certain components in plants. Despite these drawbacks, conventional
methods continue to be widely used due to the easy availability of extraction equipment
and their lower cost compared to advanced alternatives [66]. The advantages and disadvantages of traditional extraction methods are shown in Table 2.2.
2.3.3.2 Maceration
Maceration is a simple and widely used extraction method. This technique is based on
leaving crushed or powdered plant materials in contact with a solvent at room temperature. Over a period of two to three days, frequent stirring ensures adequate diffusion of the solvent into the plant sample. As the cell walls of the plant weaken and
Water
Tannins
Anthocyanins
Terpenoids
Saponins
Lectins
Ethanol
Flavonols
Polyphenols
Alkaloids
Terpenoids
Tannins
Sterols
Flavonoids
Methanol
Polyphenols
Flavones
Anthocyanins
Terpenoids
Tannins
Lactonens
Saponins
Dichloromethanol
Terpenoids
Chloroform
Flavonoids
Terpenoids
Ether
Alkaloids
Terpenoids
Coumarins
Fatty acids
Acetone
Flavonols
Figure 2.12: Commonly used solvents for the extraction of secondary metabolites.
Chapter 2 Methods of obtaining drugs from medicinal and aromatic plants 69
70 İrem Yıldız Özbaş, Severina Pacifico, and Emre Özbaş
Table 2.2: The advantages and disadvantages of traditional extraction methods.
Method Advantages Disadvantages References
Maceration Low-cost and simple
equipment
Ease of application
Decoction Efficient for water-soluble
bioactive compounds
Avoiding the degradation of
stable compounds
Infusion Simple
Accessible
Percolation Highly efficient Excessive solvent consumption
Soxhlet extraction Low cost
Continuous contact with the
solvent
No filtration required after the
process
Simple equipment and simple
method
Suitable for the extraction of
large amounts of material
Hydrodistillation and
steam distillation
Low cost Low extraction yield
Limited to heat-resistant
components
Long extraction time
Low productivity
Not suitable for the extraction of
heat sensitive constituents
Long extraction time
Energy-intensive
Not suitable for heat-sensitive
compounds
Excessive energy consumption
Long extraction time
Long extraction time
Requires large amounts of solvent
Difficulty in automation
Limitations in solvent selection
Exposure to hazardous and
flammable organic solvents
Unsuitability for shaking and
stirring
Partial loss of volatile components
Lengthy processing times
[58]
[67]
[68]
[69]
[68]
[69]
[8, 47, 48,
50]
[67]
break down, the phytochemical components within the plant begin to dissolve in the
solvent. At the end of the extraction stage, a filtration process is carried out [8].
During this process, periodic shaking is crucial for effective extraction. If the container is a bottle, occasional shaking is recommended. After the extraction period, the
liquid extract, known as the miscella, is separated from the solid residue, called marc,
using methods such as filtration or decantation. Then, the miscella is isolated from
the menstruum by evaporating the solvent using an oven or water bath [70].
Maceration can be used to extract coarse powdered plant materials such as
leaves, bark, or root bark [71]. This method allows for the extraction of various phytochemicals, including polyphenols, flavonoids, alkaloids, tannins, coumarins, terpenoids, polypeptides, glycosides, steroids, quinones, and saponins. Solvent selection is
crucial in determining the bioactive compounds to be extracted. For example, ethanol
effectively extracts glycosides, alkaloids, and carbohydrates, while water is suitable
Chapter 2 Methods of obtaining drugs from medicinal and aromatic plants 71
for terpenoids, alkaloids, glycosides, and carbohydrates. On the other hand, methanol
is effective in extracting phenolic compounds, flavonoids, tannins, glycosides, and
amino acids [69].
This simple solid-liquid extraction method is notably advantageous for extracting
thermolabile components [72]. However, it has limitations such as long extraction
times and relatively low efficiency [67].
2.3.3.3 Infusion
Infusions are preparations in the form of dilute solutions containing easily soluble
components of raw plant materials. Fresh infusions are typically obtained by soaking
solid materials in cold or hot water for a short period of time [73].
The basic principle of the infusion method involves moistening raw materials, cut
into appropriately sized pieces, with a small amount of water for about 15 min. The
concentrated infusion is then diluted with water up to 10 times its volume. Modified
filtration or maceration processes may be used in the preparation of concentrated infusions. After dilution with water, concentrated infusions are similar to fresh infusions in terms of strength and aromatic properties. Infusions are prone to fungal and
bacterial growth [74].
This method is a convenient way to isolate heat-stable compounds from plants. It
is simple and accessible because it does not require expensive equipment or highly
skilled practitioners. However, a significant disadvantage of this technique is that
heat-sensitive plant compounds may degrade during the process, making them unsuitable for extraction [68].
2.3.3.4 Decoction
This method is based on boiling dry or wet plant parts with water for a certain period.
Woody plant materials such as roots and bark are processed with this method to extract heat-resistant components, resulting in a higher yield of water-soluble compounds [70].The preparation involves heating the required amount of herbs with
water for 30 min until approximately 50% of the water evaporates. The vessel must
remain closed during the heating process to prevent the loss of essential volatile compounds [75].
It is suitable for extracting hard and fibrous plant parts such as fruits, roots, and
shells that carry active ingredients and are stable under high heat [68]. After boiling,
water used as a solvent is removed with the help of a vacuum evaporator, leaving
behind a concentrated extract referred to as “quath” or “kwath.” [76].
This traditional decoction method ensures that the water-soluble bioactive compounds are efficiently extracted from plant materials while avoiding the degradation
72 İrem Yıldız Özbaş, Severina Pacifico, and Emre Özbaş
of stable compounds. However, the process is not suitable for thermolabile or volatile
compounds, which may be lost during heating [77, 78].
Finally, although the decoction method is a widely used technique for the extraction of plant compounds, it has several limitations. The most obvious disadvantage of
this method is that it is costly in terms of energy and time due to the long-term boiling
and high temperature requirements. In addition, it can reduce the extraction effectiveness by causing the decomposition of heat-sensitive components and the evaporation of volatile components. The method also leads to the extraction of unwanted
water-soluble substances, which negatively affects the purity of the product obtained.
The difficulty of standardization is another important problem of the decoction
method; the composition of the product can differ based on the quality of the plant
material and the process parameters. While the voluminous extracts resulting from
the use of high amounts of water require additional concentration processes, the
need for more raw materials for hard-textured plants can increase the cost. These limitations prevent the decoction method from being preferred in all cases and encourage the use of alternative extraction techniques [69].
2.3.3.5 Percolation
Percolation is an effective and widely used method for extracting active components
from plant materials, offering a more controlled extraction process compared to maceration. The term is derived from the Latin word percolo, meaning “to flow through,”
and the process involves gradually passing a solvent drop by drop through a solid material. The percolation technique is simple in terms of equipment and easy to perform.
In this technique, the powdered sample is tightly filled into a tank called a percolator,
moistened with the solvent, and then continuously infused with the extraction solvent
while the extract is simultaneously collected. Common solvents include ethanol,
water, or hydro-alcoholic mixtures, and the process continues until the eluate becomes colorless. After extraction, the residual plant material is pressed to recover the
absorbed solvent. The recovered solvent is then combined with the collected extract,
and evaporation is used to produce a concentrated extract [79].
Since percolation involves the continuous addition of fresh solvent to a saturated
solution, it is both efficient and effective [80]. The technique is suitable for extracting
components that are unstable under thermal conditions. Additionally, it preserves the
quality and concentration of the final product while achieving high extraction efficiency. However, disadvantages include high solvent consumption, long extraction
times, and increased energy requirements during subsequent concentration processes
[81, 82].