Abstract
The flavonoids are compounds synthesized by plants, and they have properties such as antioxidant, anticancer, anti-inflammatory, and antibacterial, among others. One of the most important bioactive properties of flavonoids is their antioxidant effect. Synthetic antioxidants have side toxic effects whilst natural antioxidants, such as flavonoids from natural sources, have relatively low toxicity. Therefore, it is important to incorporate flavonoids derived from natural sources in several products such as foods, cosmetics, and drugs. For this reason, there is currently a need to extract flavonoids from plant resources. In this review are described the most important parameters involved in the extraction of flavonoids by unconventional methods such as ultrasound, pressurized liquid extraction, mechanochemical, high hydrostatic pressure, supercritical fluid, negative pressure cavitation, intensification of vaporization by decompression to the vacuum, microwave, infrared, pulsed electric field, high-voltage electrical discharges, and enzyme-assisted extraction. There are no unified operation conditions to achieve high yields and purity. Notwithstanding, progress has been achieved in the development of more advanced and environmentally friendly methods of extraction. Although in literature are found important advances, a complete understanding of the extraction process in each of the unconventional techniques is needed to determine the thermodynamic and kinetic mechanisms that govern each of the techniques.
Highlights
Since ancient times, mankind has benefited from the nutritional and medicinal properties of cereals, legumes, pseudocereals, stems, roots, leaves, fruits, vegetables and their coproducts
The main parameters and operating conditions of unconventional methods for the extraction of flavonoids were analyzed. Such techniques included Ultrasound extraction (UE), Pressurized liquid extraction (PLE), Mechanochemical-assisted extraction (MAE), High hydrostatic pressure extraction (HHPE), Enzyme-assisted extraction (EAE), supercritical fluid extraction (SFE), microwave-assisted extraction (MWAE), IR, Pulsed electric field (PEF), Negative pressure cavitation extraction (NPCE), and highvoltage electrical discharge (HVED). ese techniques represent the attention of mankind to improve the quality of life and the good preservation of the environment. ey have represented the ability of researchers to create innovative processes to improve the extraction of flavonoids from plant material
It would be important to conduct thermodynamic studies because only a few were found in the literature. ermodynamic studies might help to complete the knowledge of equilibrium and the limits of extraction at different temperatures
Summary
Mankind has benefited from the nutritional and medicinal properties of cereals, legumes, pseudocereals, stems, roots, leaves, fruits, vegetables and their coproducts. Such properties are attributed to phytochemicals associated to these tissues. Ey help to prevent the oxidation of fats and to protect the vitamins and enzymes in plants. For these applications, mankind has attempted to extract plant flavonoids by creative methods. Rough the years, variations in these methods widened and improved the extraction of phytochemicals using more sophisticated equipment (unconventional methods). This review presents a general description of equipment and processes, the main parameters and operating conditions utilized during extraction, and the perspectives of these different methods
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