The polarity/ionic strength of various solvents in use, along with the usage of heat and/or mixing, are the key factors influencing the effectiveness of conventional extraction processes [87]. Soxhlet extraction, maceration, solvent extraction, reflux extraction, etc. are examples of traditional extraction techniques. In maceration, the sample is ground into fine particles to enhance its surface area and facilitate solvent mixing (water or an organic solvent). The solvent is then combined with the ground materials, followed by continuous agitation, and contaminants are later removed using filtration. The relatively simple extraction technique of maceration has the drawbacks of a lengthy extraction period and poor extraction effectiveness. However, thermolabile components could be best extracted using maceration. Another extraction method that is more effective than maceration is percolation. It is an unceasing process that utilizes a special piece of machinery called a percolator, in which the saturated solvent is continuously changed out for a new solvent. The percolator is typically filled with dried powdered samples, which are then mixed with boiling water and macerated for a few hours. To obtain concentrated extracts, evaporation is carried out after the completion of extraction [88]. Another common extraction method is called decoction, which involves boiling the crude aqueous extract to a pre-determined volume for a specific amount of time to extract the heat-stable components. The liquid is allowed to cool and is strained or filtered after it settles. The method can be used to extract water-soluble components. It should be noted that this process is ineffective for materials that are sensitive to heat and light, and volatile or thermolabile substances cannot be obtained using decoction. In addition, mass transfer and kinetic effects must be taken into account [64]. Compared with percolation or maceration, reflux or solid–liquid extraction is more effective, uses less solvent, and has a shorter extraction time [87]. This procedure involves mixing a dry sample with the solvent in a heated, agitated jar. Better mass transfer and contact efficiency between the solvent and the treated matrix are gained when the vapors are allowed to condense and trickle back into the flask. Compounds with high thermolability cannot be extracted using this method [75]. Soxhlet extraction has long been the most extensively operated method for concentrating analytes and separating bioactive components from natural materials. Utilizing the principles of reflux and siphoning to constantly extract the bioactive component with fresh solvent, the Soxhlet extraction process combines the benefits of both percolation and reflux extraction. Compared with maceration or percolation, the Soxhlet extraction process has a high extraction efficiency, takes less time, and has lower solvent consumption. However, the high temperature and prolonged heat exposure could increase the thermal degradation of the bioactive compounds [69].

Numerous studies have demonstrated the effectiveness of traditional extraction techniques, including the Soxhlet extraction and maceration processes. However, using such techniques requires the use of a lot of time, energy, and solvent. There are alternative extraction methods that have faster extraction times, higher selectivity, and higher efficiency, and use less solvent to overcome the disadvantages of conventional extraction procedures. These procedures are referred to as non-conventional or green extraction methods, or novel extraction methods [89]. The application of novel technologies, such as ultrasound and pulsed electric fields, to grapes has increased the polyphenol content by 32–23% and decreased the energy consumption by 17.6 fold [90]. Some of the promising non-conventional extraction techniques are discussed below.

Since Hannay and Hogarth’s discovery of supercritical fluid in 1879, it has been utilized for extraction purposes, and in 1964, it was employed in the food industry to decaffeinate coffee [58]. SFE has gained popularity in recent years as a method for extracting bioactive components from plants at atmospheric temperatures while avoiding thermal denaturation. Supercritical fluid (SF) is used as the extraction solvent in supercritical fluid extraction. A substance can only reach the characteristic supercritical state if it is subjected to pressure and temperatures beyond its critical point. Supercritical fluid exhibits liquid-like density and solvation power, and gas-like viscosity, surface tension, and diffusion characteristics in its supercritical state. These characteristics allow for faster and higher-yielding chemical extraction. Due to its low critical temperature (31 °C), inertness, low cost, and non-toxicity, supercritical carbon dioxide is frequently utilized in SFE. The main aspects that affect the extraction efficiency of SCF extraction are the process temperature, pressure, flow rate, and sample volume [73]. The efficiency of SFE in extracting bioactive components from plant matrices has been reported in various studies [91]. SFE can be used to extract alkaloids, such as Pyrrolidine [92], caffeine [93], Olchicine [94], and Vinblastine [95], essential oils [96], terpenes [97], flavonoids [98], and phenolic compounds [99].

The microwave-assisted extraction technique is regarded as a novel practice that uses microwave radiation to extract soluble compounds into a fluid from a variety of matrices. Electromagnetic radiation with frequencies between 300 MHz and 300 GHz is known as microwaves [100]. They are composed of electric and magnetic fields that oscillate perpendicular to each other. The microwave heating principle relies on the dipole rotation and ionic conduction mechanisms. The resistance of the medium to the flow of ions during ionic conduction causes heat to be produced, whereas the electromagnetic field change brought on by microwave radiation will frequently cause changes in molecular orientation, thereby producing heat by molecular friction [101]. The high extraction yield in MAE is due to the synergistic effect of the heat and mass gradients. MAE involves three stages; first, the solvent’s penetration into the plant matrix, followed by the breakdown of the components by electromagnetic waves, and the transport of the solubilized components from the insoluble matrix to the bulk solution. Finally, liquid and residual solid phase separations are performed [102]. MAE can be used to extract a variety of bioactive components, such as flavonoids [103], isoflavone [104], saponins [105], piperine [106], carotenoids [107], terpenes [108], essential oils [109,110], polysaccharides [111], etc.

The phytochemicals in plant matrices can be either disseminated in the cell cytoplasm or found attached to the polysaccharide–lignin network by hydrogen or hydrophobic interactions, making the compounds inaccessible for extraction using a solvent in a typical extraction technique [102]. It has been suggested that enzymatic pre-treatment is a novel and efficient method for releasing bound molecules and improving the total yield. To acquire bioactive chemicals, enzyme-assisted extraction (EAE) can be used as a pre-extraction or extraction procedure. The plant cell wall is destroyed, releasing the bound bioactive chemicals attached to the lipid and carbohydrate chains [76,77]. The major enzymes that are used in EAE are cellulases [112], pectinase [113], hemicellulase [114], amylase [115], glucosidase [116], etc. EAE can be used for extracting bioactive components such as anthocyanins [117], polyphenols [118], oleoresin [119], flavonols [120], terpenes [121], carotene [122], etc.

Pulsed Electric Field Extraction (PEFE) promotes mass transfer during extraction by breaking down membrane structures, thereby considerably enhancing the extraction yield and decreasing the extraction time. The cell membrane experiences an electric potential when it is deferred in an electric field, and when the electric potential exceeds a critical value, repulsion between charge-carrying molecules creates pores in vulnerable regions of the membrane, dramatically increasing permeability. The field strength, pulse count, specific energy, and treatment temperature are all factors that affect PEFE treatment [123]. Due to its energy efficiency, PEFE processing is a feasible technique for the food, pharmaceutical, and biotech industries. PEFE can be used for extracting polyphenols [80], flavonoids [79], proteins [81], anthocyanins [82], and carbohydrates [78].

High-pressure extraction, also known as pressurized liquid extraction (PLE), accelerated solvent extraction, enhanced solvent extraction, or pressurized fluid, involves using a high pressure to keep solvents in the liquid state above their usual boiling point. The high pressure maintains solvents in a liquid condition above their boiling point, leading to high lipid solubility, high lipid solute diffusion rates, and high solvent penetration of the matrix [124]. Compared with other procedures, PLE significantly reduces the extraction time and amount of solvent used and has excellent repeatability. High-pressure extraction has been effectively used by researchers to extract an array of bioactive components, such as phenolic compounds, carotenoids, flavonoids, pectin, etc. [83].

With frequencies between 20 kHz and 100 MHz, ultrasound is a specific kind of sound wave that is not audible to humans. Similar to other waves, it compresses and expands the medium as it travels through it. This process causes a phenomenon known as cavitation, which denotes the formation, expansion, and collapse of bubbles. This event releases a significant amount of energy, which causes cell rupture [86]. The process of applying intense ultrasonic waves for extraction is known as ultrasound-assisted extraction (UAE). The technology is renowned for its ease of use and relative affordability when compared with other traditional extraction methods. Moreover, UAE has lower solvent usage, a shorter extraction time, and lower energy consumption. Sonication can also facilitate efficient mixing and quicker energy transfer. UAE is an efficient technique for the extraction of bioactive compounds, such as polyphenols, flavonoids, anthocyanins, etc. from various plant matrices [58,84,85,86].