Medicinal Plant Research 2025, Vol.15, No.2, 88-98 http://hortherbpublisher.com/index.php/mpr 91 Microwave-assisted extraction (MAE) relies on microwave heating to rapidly increase the temperature of the solvent and sample, thereby enhancing the extraction efficiency and selectivity. These two methods share a common feature: they use less solvent and consume less energy, and thus are regarded as more environmentally friendly options. At the same time, they are also milder to heat-sensitive flavonoids and preserve their activity better. In addition to physical methods, biological means have also begun to be incorporated. Enzymatic hydrolysis method breaks down the cell wall structure through specific enzymes and releases flavonoids without destroying the activity of components (Wang et al., 2024). As for SFE, it uses supercritical CO2, which has a low temperature, strong selectivity and almost no residue, and can retain the activity of flavonoids to the greatest extent (Huang et al., 2017; Chaves et al., 2020). 3.3 Optimization and comparison of extraction parameters To extract more and better flavonoids, the regulation of extraction parameters is an unavoidable step. The most common approach is to conduct single-factor experiments, that is, to adjust one variable at a time, such as adjusting basic conditions (e.g., solvent concentration, temperature, and extraction time), to determine which combination is the most appropriate (Liu et al., 2022). However, this approach is safe, it is not very efficient. Later, statistical modeling methods, like the Response Surface Method (RSM), came in handy. It can analyze the interaction relationship among multiple variables at one time and predict the optimal extraction condition more accurately (Wang et al., 2024). However, talking too much is not enough. When comparing different extraction methods, one should not only focus on the yield and purity, but also consider practical issues such as cost, environmental friendliness, and whether they can be widely applied. Judging from the current situation, green extraction technologies such as UAE, MAE, enzymatic hydrolysis, and SFE do have more advantages over traditional methods in terms of efficiency, selectivity, and environmental friendliness (Chaves et al., 2020; Wang et al., 2024). But, it's not without thresholds. For instance, SFE, although it has a good purification effect, has relatively high requirements for equipment and operation, which may be unaffordable for small laboratories or small and medium-sized enterprises (Huang et al., 2017). 4 Separation and Purification of Hangbaiju Flavonoids 4.1 Chromatographic separation techniques Macroporous resin adsorption method, is one of the important techniques for the preliminary enrichment and separation of flavonoids in Hangbaiju. It takes advantage of the large specific surface area, and strong selective adsorption capacity of macroporous resins, and can efficiently capture flavonoids. Selective desorption and grading of flavonoids can be achieved, by using solvents with gradually increasing polarity for gradient elution, improving purity and facilitating subsequent analysis or product preparation (Zhu et al., 2024). High performance liquid chromatography (HPLC), is the key technology for identifying, quantifying and preparing and separating the monomer flavonoids in Hangbaiju. HPLC can be used to detect key components, such as apigenin-7-O-glucoside, luteolin and trilobin, and is an important means for quality control and the development of functional food components (Gong et al., 2019; Yang et al., 2022). The method based on HPLC can also be used to identify different cultivated varieties of Hangbaiju, according to the flavonoid profile (Gong et al., 2019). 4.2 Membrane separation and novel purification methods Membrane separation technologies (e.g., nanofiltration, ultrafiltration), are gentle and efficient means suitable for concentrating and purifying flavonoids from aqueous extracts. These technologies can selectively retain macromolecular compounds while allowing small-molecule impurities to pass through, thereby enhancing the purity of the flavonoid portion. This type of method has significant advantages for large-scale processing, and maintaining the biological activity of active ingredients (Zhu et al., 2024).
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