INTRODUCTION:

Herbal medicines have been used for centuries and continue to play a vital role in healthcare, with 80% of the global population relying on them. Despite advances in modern medicine, the demand for herbal drugs is rising due to their safety, efficacy, cultural acceptance, and fewer side effects. The resurgence of herbal medicine is driven by concerns over the side effects of modern drugs and the lack of treatments for many chronic diseases. To ensure quality and effectiveness, a systematic approach and standardized methodologies for herbal raw materials and formulations are needed.¹ Ancient texts like the Ebers Papyrus, Charaka Samhita, and Materia Medica highlight the long history of using plant-based substances for healing. These traditional practices helped shape modern herbal medicine, promoting a holistic approach to health that considers the mind, body, and spirit.²

The study of medicinal plants begins with pre-extraction and extraction processes to obtain bioactive compounds. The choice of an extraction process is contingent upon criteria such as the type of material, preparation process, and energy usage, aiming to maximize yield while minimizing loss and energy consumption Sample preparation accounts for about 60% of the total time while the final analysis using spectroscopic or chromatographic methods takes up only 7% Incorrect extraction techniques can lead to loss of the desired component and misinterpretation of results.³

Traditional methods like Maceration and Soxhlet extraction are commonly used in small-scale research and production, while modern methods like microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE), and supercritical fluid extraction (SFE) offer higher yields at lower costs. Ongoing advancements and modifications in these techniques require careful evaluation to choose the most suitable method. This review explores the principles, strengths, and limitations of common extraction methods with recent examples to aid in method selection.⁴

Different extraction methods and advanced extraction techniques:

Extraction:

The process of extracting bioactive substances from plants, such as antioxidants and essential oils, for use in a variety of products, such as tablets, lotions, or capsules, is known as herbal extraction. It is essential to maintaining the quality of natural drugs.⁵ For thousands of years, people have used natural medicines to prevent and treat diseases, and natural ingredients are important sources for the drug development. Nevertheless, these goods frequently include trace amounts of beneficial chemicals. This paper aims to explore various methods for extracting and isolating bioactive natural products, discussing both traditional and modern techniques along with their advantages, drawbacks, and examples. To separate the required natural advancements from the natural materials, extraction is the initial stage. Among the extraction methods are solvent extraction, distillation using the extraction principle for sublimation and scraping.

Steps of extraction:

The following phases make up the drug extraction process:

· The solvent reaches the drug.

· The solvent contributes to the drugs ingredients to dissolve.

· Diffusion has occurred within the cells from the solution.

· After the medication has been used up, the dissolved portion separates.

· A mass transfer process occurs during the extraction process, transferring mass from a soluble material, such as a solid, to a fluid. Several factors including such as the temperature, agitation, size reduction, and others, influence the mass transfer process.⁶

Traditional method of extraction:⁵

1. Maceration

2. Digestion

3. Decoction

4. Infusion

5. Percolation

6. Soxhlet extraction

1. Maceration: In this process 750 ml of the recommended solvent is added to a stoppered container containing the solid ingredient, and the mixture is let to stand for a until the soluble matter is dissolved, which should take at least three days in a warm environment with continuous stirring. After the majority of the liquid has drained, the mixture is filtered. A suitable amount of the recommended solvent or solvent mixture is used to wash the residue on the filter once it has been sufficiently drained, and the filtrates are mixed to create 1000 ml. ⁶

2. Digestion: In this type of maceration, the extraction process involves the use of mild heat. It is employed when a slightly elevated temperature is acceptable, resulting in enhanced solvent efficiency of the menstrum.⁷The extraction solvent is added to a glass vessel, followed by pulverized plant material. The mixture is then placed in a water bath or oven at 50°C. Heat helps throughout the process by reducing solvent viscosity and enhancing the extraction of secondary metabolites.⁸

3. Decoction: A technique that involves boiling hard plant materials, such as roots, bark, and seeds, in water for a long time in order to extract materials.⁷ Decoction involves boiling dried, broken, or powdered plant materials to reduce their volume and concentrate bioactive compounds. Typically, the volume is reduced to 1/8th of the original; for softer materials, it's reduced to 1/4th, and for harder materials, to 1/16th. Aqueous ethanol or glycerol can sometimes be used instead of water.⁹

4. Infusion: A technique that involves steeping plant materials in hot water or another solvent to extract compounds from dried leaves, flowers, or herbs.¹⁰ The drug is placed at the bottom of an infusion pot, water is added, and the mixture is stirred occasionally. Alternatively, the drug can be wrapped in muslin cloth and suspended just below the water level for about 15 minutes. This quick process is used for soft drugs with water-soluble active compounds. The infusion should be consumed within 24 hours of preparation, though a concentrated version with alcohol can be stored for a longer period.¹¹

5. Percolation: A traditional technique for removing active ingredients from fluid extract is percolation. It is made up of a narrow percolator, which is typically formed like a cone. After completely mixing the ingredient sample with water, the solution is poured into a closed container from the top through the column. The pure extract is obtained when the mixture gradually moves down (24–48hours, depending on the sample). To achieve the required concentration, the enhanced wet extract is concentrated in evaporators. Numerous polyphenolics have been isolated from the matrices using this approach.¹²

6. Soxhlet Extraction: Soxhlet extraction is a broad extraction technique that is commonly applied to analytes that are sufficiently thermally stable. The solvent used for extraction is continually cycled through the matrix through condensation and boiling, while the sample is gathered in the heated solvent (polar or non-polar). Apart from the extraction solvent selection, the method is not selective, and additional cleanup and concentration are typically needed. The extraction time (typically 1–6 hours) can be reduced by using automated systems that allow for the extraction of multiple samples simultaneously. Although automated systems enable the use of smaller solvent quantities, A substantial amount of organic solvent is needed for the traditional methods (50–200 ml for a 10-g sample). In an attempt to improve the technique, it has also been combined with ultrasonic extraction and microwave-assisted extraction efficiency of extraction. The detection of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) are two instances of how Soxhlet is used for trace contamination analysis.¹³

Advanced extraction methods:

· Supercritical fluid extraction

· Microwave assisted extraction

· Ultrasound assisted extraction

· Pressurized liquid extraction

· Enzyme assisted extraction

· Pulsed electric field assisted extraction

1. Supercritical fluid extraction:

When a gas like carbon dioxide is compressed and heated, it becomes a supercritical fluid, exhibiting both gas-like diffusion and liquid-like dissolving abilities¹⁴. This unique combination makes supercritical fluids ideal for chemical, biological, and polymer extraction processes. Supercritical fluid extraction (SFE) is a technique that uses a supercritical fluid to extract targeted components from substances based on differences in solubility.³⁰

Advantages of SFE:

1. Its low operating temperature and effective solvent use

2. Decreased energy needs and improved product quality because there is no solvent residue.

3. The selective character of supercritical fluid extraction, which is accomplished by carefully regulating temperature and pressure throughout the extraction procedure.

Disadvantages of SFE:¹⁵

1. Its low flavonoid output limits its broad use in propolis processing.

2. High cost.

3. Substantial utilization of energy and improper use of raw materials.

Fig. 1: Supercritical Fluid Extraction ¹⁶

2. Microwave assisted extraction:

Microwave are non-ionizing electromagnetic waves where the frequency range is from 300MHz to 300GHz. The 915 MHz frequency is ideal although 2,450 MHz is frequently utilized in home microwave ovens and extraction applications, such as analytical chemistry, for industrial applications because of its deeper penetration. Maxwell's equations control the electromagnetic (EM) energy distribution in microwave-assisted systems, influenced by system configuration and material interfaces.¹⁷The effectiveness of EM energy coupling, field distribution, and its conversion into thermal energy within biological samples are all significantly influenced by the samples' dielectric characteristics.¹⁸

Types of Microwaves Assisted Extraction:

1. Open vessel: Only a portion of the vessel is exposed to microwave radiation in an open system, which runs at atmospheric conditions. To condense any evaporated solvent, the upper portion is attached to a reflux machine.⁵

2. Close vessel: High pressure and temperature are used for a quick and effective extraction process in a sealed vessel that is uniformly heated by microwaves. While the temperature is controlled above the solvent's typical boiling point, the pressure is maintained below the vessel's maximum limit.⁵

Advantages of MAE:

1. Fast extraction method.

2. High efficiency in extraction.

3. 3.Suitable for extracting a wide range of bioactive chemicals, including heat-sensitive ones.

Disadvantages of MAE:¹⁷

1. Specific microwave equipment is needed.

2. Hot areas and uneven heating are possible.

3. Restricted capacity to scale.

Fig. 2: Microwave Assisted Extraction ¹⁹

3. Ultrasound assisted extraction:

Ultrasound is a promising technology with various applications in fields like pharmaceuticals, cosmetics, chemistry, and food industries. It is a mechanical wave that requires an elastic medium to propagate and has a frequency range above 20 kHz, differing from audible sound (16 Hz to 20 kHz). There are two main types used in the food industries diagnostic (high-frequency) ultrasound (2 MHz to 10 MHz) for medical imaging and defect detection, and power (low-frequency) ultrasound (20 kHz to 100 kHz) used in applications like sonochemistry, cutting, and plastic welding. These ultrasound types are characterized by power, frequency, wavelength, and intensity, with low-frequency ultrasound facilitating chemical reactions and other industrial processes.²⁰

Ultrasonic systems consist of a transducer that converts electrical energy into sound energy, generating ultrasound. The most common and efficient type is the piezoelectric transducer, which operates using a crystalline ceramic material and achieves over 95% efficiency. The ultrasound is emitted by a reactor that may also amplify the waves. The most widely used emitters are bath and probe systems, with the probe often having a sonotrode (horn) that amplifies the waves. The shape of the horn controls the intensity of the ultrasound. Equipment is available for both laboratory and industrial scales, with recent advancements in continuous-flow systems. Future improvements are expected in coupling ultrasonic equipment with analytical instruments to reduce costs by eliminating sample preparation steps.²¹

Advantages of UAE:²²

1. Better extraction yields and increased bioavailability are attained in the UAE.

2. They can efficiently pierce plant cell walls with ultrasonic vibrations, causing cell rupture or deformation.

3. Higher extraction rates are produced by this method, which makes it easier to extract bioactive chemicals more thoroughly.

Disadvantages of UAE: ²³

1. Restricted to uses on a limited scale.

2. Possible deterioration of certain bioactive substances as a result of localized high temperatures.

Fig. 3: Ultrasound Assisted Extraction ²³

4. Pressurized liquid extraction:

A novel technique for removing chemicals from algae is called Pressurized Liquid Extraction (PLE), which uses high pressure and temperature to keep the extraction solvent liquid. When water is used as the solvent, it is referred to as Subcritical Water Extraction (SWE) or Pressurized Hot-Water Extraction (PHWE), but it is also known as Accelerated Solvent Extraction (ASE). Higher extraction rates and less solvent use are the results of the technique's improved analyte solubility, faster mass transfer, and decreased solvent viscosity and surface tension.²⁴

Advantages of PLE:

1. Quick extraction procedure.

2. High extraction effectiveness while using less solvent.

3. Beneficial for a variety of bioactive substances.

Disadvantages of PLE:²⁵

1. High equipment initial cost.

2. Restricted to substances that are heat-stable.

Fig. 4: Pressurized Liquid Extraction ²⁶

5. Enzyme assisted extraction:

Hydrolytic enzymes like cellulase and pectinase are used in Enzyme-Assisted Extraction (EAE) to break down plant cell walls and increase extraction yields. Pectinase breaks down pectin in the primary and middle lamella cell walls, whereas cellulase targets the cellulose in the cell walls. This technology is cost-effective since it offers an environmentally benign substitute for harsher techniques and has the benefit of reusing enzymes. Furthermore, EAE makes it easier to use enzymes in medical analysis.²⁷

Advantages of EAE:

1. Mild extraction conditions (pH and ambient temperature).

2. High yield and specificity.

3. Preservation of the chemicals' integrity and bioactivity.

Disadvantages of EAE:²⁸

1. Enzymes are expensive.

2. Demands that temperature, pH, and enzyme concentration be optimized.

Fig. 5: Enzyme Assisted Extraction ²⁸

6. Pulsed electric field assisted extraction:

A cutting-edge method called pulsed electric field (PEF) extraction uses brief bursts of strong electric fields to draw out bioactive substances. When the sample is positioned between two electrodes, electric field pulses of 20–80 kV/cm in continuous mode or 100–300 V/cm in batch mode are produced. The procedure depends on how many pulses are given to the sample.²⁹ PEF helps extract compounds through two mechanisms: enhancing solvent solubility in biological membranes and speeding up chemical reactions, or by electroporating the cell membrane, making it easier to release bioactive substances.³¹

Advantages of PEF:

1. Heat-sensitive chemicals are preserved using a non-thermal approach.

2. brief extraction period.

3. Low usage of energy

Disadvantages of PEF²⁷:

1. Only samples that are liquid or semi-liquid.

2. The equipment's high initial cost and complexity.

Fig. 6: Pulsed Electric Field Assisted Extraction ²⁸

CONCLUSION:

The increasing global reliance on herbal medicine demands more efficient and standardized extraction technologies. Traditional methods, while accessible and simple, often fall short in yield and efficiency. In contrast, modern techniques like SFE, MAE, UAE, EAE, PLE, and PEF provide scalable, faster, and more selective extraction options, preserving bioactive integrity and supporting pharmaceutical development. Future trends should focus on combining methods, improving green extraction technologies, and developing scalable systems to meet the growing demand for safe and effective herbal drugs.

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Received on 16.04.2025 Revised on 12.06.2025

Accepted on 14.07.2025 Published on 24.07.2025

Available online from July 28, 2025

Res. J. Pharmacognosy and Phytochem. 2025; 17(3):229-234.

DOI: 10.52711/0975-4385.2025.00037

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