Extraction and separation of flavonoids and iridoids from Eucommia ulmoides leaves using choline tryptophan ionic liquid-based aqueous biphasic systems

The choline tryptophan ionic liquid (IL)-based aqueous biphasic system (ABS) was designed and applied to extract and separate flavonoids and iridoids from Eucommia ulmoides leaves. This ABS possessed a unique viscous layer enriching iridoids that can be directly removed at the interface between the IL-rich and salt-rich phases. The extraction yield of total flavonoids was optimized by RSM to obtain a predicted maximum of 2.91% at the IL concentration of 36.73%, liquid to solid ratio of 38, extraction temperature of 44 °C and extraction time of 105 min. The determined extraction yield of total flavonoids is 2.78% ± 0.12% under revised optimization conditions. The distribution coefficient K and extraction rate E of total flavonoids in the IL-rich phase reach the maximum of 129% and 98.53% at the K3PO4 content of 26% in the ILABS, respectively. The HPLC analysis shows a high content of rutin in the flavonoids precipitate induced by water as an anti-solvent. Aucubin content reaches 15.19% in the intermediate viscous layer enriching iridoids. Hence, the designed process has the potential to be applied to the separation and enrichment of rutin and aucubin from other industrial crops.