Green Extraction of Forsythoside A, Phillyrin and Phillygenol from Forsythia suspensa Leaves Using a β-Cyclodextrin-Assisted Method

In this study, a green process of β-cyclodextrin (β-CD)-assisted extraction of active ingredients from Forsythia suspensa leaves was developed. Firstly, the optimal process of extraction was as follows: the ratio between Forsythia suspensa leaves and β-CD was 3.61:5, the solid–liquid ratio was 1:36.3, the temperature was 75.25 °C and the pH was 3.94. The yields of forsythoside A, phillyrin and phillygenol were 11.80 ± 0.141%, 5.49 ± 0.078% and 0.319 ± 0.004%, respectively. Then, the structure characteristics of the β-CD-assisted extract of Forsythia suspensa leaves (FSE-β-CD) were analyzed using powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and molecular docking to demonstrate that the natural active products from Forsythia suspensa leaves had significant interactions with the β-CD. Additionally, the loss of forsythoside A from aqueous FSE-CD at 80 °C was only 12%, compared with Forsythia suspensa leaf extract (FSE) which decreased by 13%. In addition, the aqueous solubility of FSE-CD was significantly increased to 70.2 g/L. The EC(50) for scavenging DPPH and ABTS radicals decreased to 28.98 ug/mL and 25.54 ug/mL, respectively. The results showed that the β-CD-assisted extraction process would be a promising technology for bioactive compounds extracted from plants.