Flavonoids in sophora japonica extract have attracted much attention due to their antioxidant, anti-inflammatory, and cardiovascular protective activities. Their extraction efficiency is closely related to the choice of solvent system. Traditional solvents such as water and ethanol, while inexpensive, exhibit significant differences in their solubility for flavonoids. Water, as a polar solvent, has strong solubility for water-soluble components such as polysaccharides and proteins, but low solubility for flavonoids, leading to higher impurity content during extraction, complex post-processing, and limited flavonoid yield. In contrast, ethanol, with its moderate polarity and good permeability, has become a commonly used solvent for flavonoid extraction. Ethanol can disrupt plant cell walls, promoting the dissolution of flavonoids, and is non-toxic and safe. However, the selective solubility of flavonoids by ethanol alone is still limited, requiring optimization of concentration or blending with other solvents to improve yield.
Ethanol-water mixed solvents, by adjusting the ratio of ethanol to water, can significantly improve the dissolution environment of flavonoids. The addition of ethanol reduces the polarity of the solvent system, enhancing its solubility for flavonoids. Simultaneously, the presence of water helps maintain solvent fluidity and promotes mass transfer. Studies have shown that using an ethanol-water mixed solvent and adjusting the pH to weakly acidic can further enhance the solubility of flavonoids while inhibiting their hydrolysis. This solvent system not only improves the yield of flavonoids but also reduces the dissolution of impurities such as polysaccharides, thus simplifying subsequent purification steps. Compared to single solvents, ethanol-water mixed solvents exhibit higher selectivity and efficiency in flavonoid extraction, becoming an important direction for optimizing extraction processes.
The introduction of green solvents such as eutectic solvents (DES) and ionic liquids provides new ideas for the extraction of flavonoids from *Sophora japonica* extract. DES, formed by hydrogen bond acceptors and donors through intermolecular forces, possesses characteristics such as high designability, excellent solubility, and environmental friendliness. By screening DES systems with different compositions, efficient and selective extraction of flavonoids can be achieved. For example, the DES system using choline chloride as the hydrogen bond acceptor and ethylene glycol as the donor, under specific molar ratios and water content conditions, showed a significantly higher extraction rate of flavonoids such as rutin compared to traditional ethanol solvents. The synergistic effect of hydrogen bonding in DES and ultrasonic cavitation can disrupt plant cell structure, improve mass transfer efficiency, and simultaneously avoid the degradation of active ingredients by high temperatures, providing a possibility for the development of environmentally friendly extraction processes.
The optimization of solvent systems also needs to consider the feasibility of industrial production. Traditional solvent extraction methods suffer from long extraction times and high energy consumption, while the introduction of technologies such as ultrasonic-assisted extraction, microwave-assisted extraction, and supercritical CO₂ extraction can significantly shorten extraction time and increase yield. For example, ultrasonic-assisted extraction accelerates solvent penetration through cavitation, shortening the extraction time of flavonoids while increasing the yield; microwave-assisted extraction utilizes electromagnetic fields to accelerate molecular motion, achieving efficient extraction at low temperatures and avoiding the degradation of active ingredients. Supercritical CO₂ extraction technology, by adjusting temperature and pressure, can selectively extract fat-soluble flavonoids, complementing traditional water extraction processes and further improving the purity and activity of the extract.
In the process of solvent system optimization, solvent recovery and recycling also need to be considered. The recovery rate of organic solvents such as ethanol directly affects production costs and environmental pressure. By introducing a solvent recovery system, the ethanol recovery rate can be significantly improved, reducing solvent consumption and waste emissions. Furthermore, although research on the recycling of green solvents such as DES is in its early stages, its designability and environmental friendliness offer potential for the development of sustainable extraction processes. Future research needs to further explore DES recovery methods and their application in industrial production to promote the green transformation of sophora japonica extract extraction processes.
The choice of solvent system has a decisive impact on the yield of flavonoids in sophora japonica extract. From traditional water and ethanol solvents to ethanol-water mixed solvents, and then to green solvents such as DES and ionic liquids, the optimization of solvent systems is continuously driving the improvement of extraction efficiency and the greening of processes. In the future, with a deeper understanding of the mechanism of solvent molecule action and mass transfer processes, combined with extraction technologies such as ultrasound and microwave, the extraction process of flavonoids in sophora japonica extract will develop towards a more efficient and environmentally friendly direction, providing high-quality raw materials for the development of functional foods and pharmaceutical products.
