**3. Extraction methods**

Medicinal plants are becoming very important due to their uses mainly as a source of therapeutic compounds that may lead to the development of novel drugs. Most of these compounds such as phenolics and flavonoids have been reported to be important for on health including cancer prevention [38]. High content of phenolic and flavonoids in medicinal plants has been correlated with their antioxidant activities that are important in prevention of the development of age-related disease, especially those related to oxidative stress [39]. Phytochemicals in medicinal plants are very important in pharmaceuticals and cosmeceutical industry [39].

Extraction is the separation of medicinally mixture of many plant metabolites, such as alkaloids, glycosides, phenolics, terpenoids, and flavonoids using selective solvents through standard procedures [40]. The aim of all solvent extraction methods is to separate the soluble plant metabolites, leaving behind the insoluble cellular marc. The following are the widely used extraction techniques.

#### **3.1 Maceration, infusion, percolation, and decoction**

Maceration extraction method is used in wine making and also used for extraction of bioactive compounds from plants [39]. Maceration involved soaking plant materials (coarse or powdered) in a stoppered container with a solvent and allowed to stand at room temperature for at least 3 days with frequent agitation [40], which

is followed by pressing or straining and filtration. In conventional methods, heat is transferred through convection and conduction, and the solvent is selected based on the compound aimed to be extracted [40]. Infusion and decoction use the same principle as maceration but both are soaked in cold or boiled water [39].

Decoction is only suitable for extracting heat-stable compounds, hard plant materials such as roots and barks, and the process usually yielded more oil-soluble compounds compared to maceration and infusion [39].

#### **3.2 Soxhlet extraction or hot continuous extraction**

In this method, the sample is ground and placed in a porous bag called thimble made from a strong filter paper or cellulose. The thimble containing the sample is placed in thimble chamber of the Soxhlet apparatus. Extraction solvents are heated in the bottom flask, then vaporized into the sample thimble, condensed in the condenser, and dripped back which result in extraction of plant secondary metabolites in a good yield.

#### **3.3 Microwave-assisted extraction (MAE)**

This extraction method uses microwave energy to facilitate partition of analytes from the sample matrix into the solvent [41]. Microwave radiation interacts with dipoles of polar and polarizable materials such as solvent and a plant sample results heating near the surface of the materials and heat is transferred by conduction. Dipole rotation of the molecules induced by microwave electromagnetic disrupts hydrogen bonding enhancing the migration of dissolved ions and promotes solvent penetration into the matrix [42].

#### **3.4 Ultrasound-assisted extraction (UAE) or sonication extraction**

This method makes use of ultrasound ranging from 20 to 2000 kHz [40]. The mechanic effect of the ultrasound increases the surface contact between solvents and samples [39]. The ultrasound alters and disrupts the physical and chemical properties of the sample and facilitates release of compounds and enhancing mass transport of the solvents into the plant cells [43].

#### **3.5 Accelerated solvent extraction (ASE)**

Accelerated solvent extraction is more efficient solvent extraction method compared to maceration and Soxhlet extraction methods. This method makes use of minimum amount of solvent compared to maceration and Soxhlet extraction methods [39]. In ASE, sample is packed with inert packing material such as sand in the stainless steel to prevent sample from aggregating and blocking of the system tubing [39, 44]. The method controls temperature and pressure for each individual sample and the extraction completes in less than an hour [39].

#### **3.6 Supercritical fluid extraction (SFE)**

Supercritical fluid is a substance that shares the physical properties of both gas and liquid at its critical point. Temperature and pressure are the determinant factors that push a substance into its critical region [39]. Supercritical fluid behaves more like a gas but have the solvating characteristic of a liquid. For instance, CO2 becomes supercritical fluid at above 31.1°C and 7380 kPa. Interest in supercritical-CO2 extraction is quite interesting due to its excellent solvation power for nonpolar

**5**

*Introductory Chapter: Plant Extracts*

ethanol and methanol [39].

wall of a plant [52].

temperature.

*3.8.1 Purge and trap*

*DOI: http://dx.doi.org/10.5772/intechopen.85493*

**3.7 Enzyme-assisted extraction (EAE)**

**3.8 Extraction of volatile organic compounds**

sampling techniques for bioactive VOCs [53].

sampling not only VOCs but also semi-VOCs [55].

analytes. Additionally, CO2 is readily available, cheap and has low toxicity [39]. Supercritical-CO2 has poor solubility for polar compounds. The solubility of

supercritical-CO2 for polar compounds can be enhanced by adding small amount of

In some plants, some phytochemicals in their matrices are dispersed in cell cytoplasm, and secondary metabolites are retained in the polysaccharide-lignin network by hydrogen or hydrophobic bonding and are not accessible with a solvent extraction process [45]. Enzymatic pre-treatment has been considered as an effective way to release bounded compounds and increase overall yield [46]. Specific enzymes such as cellulase, a-amylase, and pectinase added during extraction enhance recovery by breaking the cell wall and hydrolyzing the structural polysaccharides and lipid bodies [46, 47]. There are two approaches for enzyme-assisted extraction method namely enzyme-assisted aqueous extraction (EAAE) and enzyme-assisted cold pressing (EACP) [48]. EAAE methods have been employed mainly for the extraction of oils from various seeds [46, 49–51]. In EACP method, enzymes are used to hydrolyze the seed cell

Distillation is the separation process of the components of a mixture of two or more liquids due to their difference in their vapor pressure. The aims of distillation process are to obtain an essential oil. Hydro-distillation (HD), steam distillation (SD), simultaneous distillation solvent extraction (SDE), microwave-assisted hydro-distillation (MWHD), supercritical fluid (CO2) extraction (SFE), purge and trap, and solid phase microextraction (SPME) [53] were employed to extract volatile organic compounds from fresh plant parts. Among these techniques, HD, SD, and SDE are classical and conventional methods for sampling bioactive volatile organic compounds (VOCs). Hydrodistillation is the distillation technique carried out either by boiling the plant materials or essential oil with water by creating the steam. The composition of the oil distillates from a mixture of two liquids depends primarily upon the boiling points or the vapor pressure at the distillation

Problems connected with conventional methods include long extraction times, large amounts of solvents, and multiple steps. Additionally, many unstable volatile organic compounds may be thermally decomposed and degraded during the thermal extraction or distillation. Because of their simplicity, these methods are still in use to extract fragrance-and-aroma oils from plants. Purge and trap, SFE, and SPME have aroused much attention from analysts as they are environment friendly

Purge and trap also known as dynamic headspace uses ultra-purified inert gas as the carrier gas to pass through samples continuously to carry out VOCs, and then VOCs are trapped in the trap that contains the sorbent such as Tenax [54]. The type of sorbent in the trap can be varied in order, and purge and trap can achieve high selectivity for different biological VOCs. Properly prolonging sampling time could also improve the enrichment effect [53]. This method has been employed for

#### *Introductory Chapter: Plant Extracts DOI: http://dx.doi.org/10.5772/intechopen.85493*

*Plant Extracts*

in a good yield.

is followed by pressing or straining and filtration. In conventional methods, heat is transferred through convection and conduction, and the solvent is selected based on the compound aimed to be extracted [40]. Infusion and decoction use the same

Decoction is only suitable for extracting heat-stable compounds, hard plant materials such as roots and barks, and the process usually yielded more oil-soluble

In this method, the sample is ground and placed in a porous bag called thimble made from a strong filter paper or cellulose. The thimble containing the sample is placed in thimble chamber of the Soxhlet apparatus. Extraction solvents are heated in the bottom flask, then vaporized into the sample thimble, condensed in the condenser, and dripped back which result in extraction of plant secondary metabolites

This extraction method uses microwave energy to facilitate partition of analytes from the sample matrix into the solvent [41]. Microwave radiation interacts with dipoles of polar and polarizable materials such as solvent and a plant sample results heating near the surface of the materials and heat is transferred by conduction. Dipole rotation of the molecules induced by microwave electromagnetic disrupts hydrogen bonding enhancing the migration of dissolved ions and promotes solvent

This method makes use of ultrasound ranging from 20 to 2000 kHz [40]. The mechanic effect of the ultrasound increases the surface contact between solvents and samples [39]. The ultrasound alters and disrupts the physical and chemical properties of the sample and facilitates release of compounds and enhancing mass

Accelerated solvent extraction is more efficient solvent extraction method compared to maceration and Soxhlet extraction methods. This method makes use of minimum amount of solvent compared to maceration and Soxhlet extraction methods [39]. In ASE, sample is packed with inert packing material such as sand in the stainless steel to prevent sample from aggregating and blocking of the system tubing [39, 44]. The method controls temperature and pressure for each individual

Supercritical fluid is a substance that shares the physical properties of both gas and liquid at its critical point. Temperature and pressure are the determinant factors that push a substance into its critical region [39]. Supercritical fluid behaves more like a gas but have the solvating characteristic of a liquid. For instance, CO2 becomes supercritical fluid at above 31.1°C and 7380 kPa. Interest in supercritical-CO2 extraction is quite interesting due to its excellent solvation power for nonpolar

**3.4 Ultrasound-assisted extraction (UAE) or sonication extraction**

principle as maceration but both are soaked in cold or boiled water [39].

compounds compared to maceration and infusion [39].

**3.2 Soxhlet extraction or hot continuous extraction**

**3.3 Microwave-assisted extraction (MAE)**

transport of the solvents into the plant cells [43].

sample and the extraction completes in less than an hour [39].

**3.5 Accelerated solvent extraction (ASE)**

**3.6 Supercritical fluid extraction (SFE)**

penetration into the matrix [42].

**4**

analytes. Additionally, CO2 is readily available, cheap and has low toxicity [39]. Supercritical-CO2 has poor solubility for polar compounds. The solubility of supercritical-CO2 for polar compounds can be enhanced by adding small amount of ethanol and methanol [39].
