**5.4 Super critical fluid extraction (SCFE)**

The extraction of thermally labile chemicals is possible because of carbon dioxide's low critical temperature (304.1 K). It can replicate a variety of organic solvents by adjusting the density of SCF carbon dioxide. Because of its variable solvating strength, this feature allows for selective extraction, purification, and fractionation techniques. SCF carbon dioxide media provide the prime possibility for fractionation of reaction products and solvent separation, which can be performed by simply depressurizing the media. This is because SCF quickly penetrates and leaves solid matrices, compared to the use of organic solvents with a higher viscosity [39]. It has a broad variety of applications, including the extraction of common spices such as black pepper, celery seed, cumin, cinnamon, clove bud, and nutmeg. Extraction of Natural Colors: Paprika Pigments, etc. Dry Ginger, Saw Palmetto, Rosemary, and other botanicals are used to extract active ingredients. Forskolin, Turmerones—from Turmeric, *Oscimum sanctum,* Neem Leaf, and other plants; Cholesterol and other lipids are extracted from dried egg yolks. Hops are extracted to use in the beverage sector. Precipitation of Human Immunoglobulin G (IgG), viral deactivation, and other biochemical components. The main disadvantage of supercritical carbon dioxide extraction is the high cost of the device. Because supercritical carbon dioxide is nonpolar, polar co-solvents of 5% and 10% ethanol were added to change the polarity and improve solubility.

#### **5.5 Microwave-assisted extraction**

Nontraditional ways are more prominent when it comes to improving the quality and quantity of desired items. By directly linking microwave energy with the bulk reaction mixture, microwave irradiation creates efficient internal heating. The magnitude of energy transfer is determined by the molecules' dielectric characteristics. Radiation absorption and heating can be quite selective in this approach (Hoz et al.). The reduction in operating time and solvent use are two major benefits of microwave treatments. However, during microwave processing, acceleration in chemical reactions of target substances such as epimerization, oxidation, and polarization should be considered with dielectric heating.

Microwave-assisted extraction without solvents is a long-term technology for extracting and separating chemicals from natural plant resources. Microwave heating is directed at the moisture content of new material. Under microwave irradiation, plant cell water and charged molecules are stimulated; this internal alteration causes a significant amount of pressure to be imposed on plant cell walls, resulting in cell swelling. Due to the rupturing of plant cells, this swelling causes an increase in the mass transfer of solutes. As a result, phytochemical leaching from the plant cellular matrix into the extractant is facilitated during MAE [40]. The best extraction conditions were a microwave power of 150 W for 90 min. Concerning the efficiency and yield of essential oils, solvent-free microwave extraction was superior. As a result, increased rates of adsorption, diffusion, and separation of phytochemicals from the plant matrix into the extracting solvent are more likely [41].

An MAE can be performed using two different types of equipment. The apparatus runs at atmospheric pressure in the open mode, which is often coupled with a refluxing mechanism. Domestic microwaves are frequently modified to accommodate this model. The closed mode, on the other hand, allows for high-pressure operation. Pumping inert gas into the extraction chamber increases the pressure. During the heating of the extraction mixture, however, vapor pressure may generate a degree of pressure. Since these molecules were stable at microwave heating settings of up to 100°C for 20 min, this approach was confined to small-molecule phenolic compounds like phenolic acids (gallic acid and ellagic acid), quercetin, isoflavones, and transresveratrol. Due to compound oxidation, more MAE cycles (e.g., from 2 10 s to 3 10 s) resulted in a considerable reduction in phenolic and flavanone yields. Because tannins and anthocyanins are prone to temperature degradation, they may not be suitable for MAE [32].

Microwave-assisted hydro distillation (MAHD) is like standard hydro distillation, with the exception that the solvent is heated using microwaves. The solvent (typically water) and plant parts are placed inside a microwave oven (normally running at 2.45 GHz), and different output powers and reaction periods can be used to improve the extraction process. Again, using microwaves for the heating process speeds up the extraction of chemicals, requiring shorter timeframes to generate comparable amounts of extracts. Furthermore, the chemical makeup of extracts obtained by standard hydro distillation and MAHD is not comparable.

#### **5.6 Pulsed electric field (PEF) extraction**

In batch mode, the electric field strength (EFS) ranges from 100 to 300 V/ cm, while in continuous mode, the EFS ranges from 20 to 80 kV/cm. An external electrical force is used in electro-permeabilization or electroporation to increase

*Green Extraction Techniques for Phytoconstituents from Natural Products DOI: http://dx.doi.org/10.5772/intechopen.105088*

the permeability of cell membranes. The cell membrane is perforated by the formation of hydrophilic holes, which result in the opening of protein channels. When high-voltage electrical pulses are applied across the electrodes, the sample experiences a force per unit charge termed the electric field. The plant material is removed once the membrane loses its structural functioning [41]. Anthocyanin, carotenoids, lycopene, lutein, polyphenols, alkaloids, lactase, protein, polysaccharides, fat, oil, and other bioactive compounds are extracted using PEF. PEFassisted extraction provides more bioactive component extracts, uses less energy, and takes less time to process, according to the study, resulting in the optimal process parameters [42].
