Extraction of triterpene acids from loquat leaves via a novel hydrophobic deep eutectic solvent screened by COSMO-SAC model

Triterpene acids (TTAs) have promising applications in functional food, medicine and other fields. Here, ultrasonic-assisted hydrophobic deep eutectic solvent (HDES) extraction was employed to gain TTAs from loquat leaves. Combining COSMO-SAC model prediction with experimental verification，the HDES, composed of thymol and benzyl alcohol (molar ratio 2:1), was proved to have the highest extraction ability for TTAs. The preliminarily optimized extraction conditions were solid to solvent ratio 1:10 (g/g), temperature 60 °C and extraction time 60 min. Under these conditions, the extraction yield of ursolic acid (the main component of loquat leaf TTAs) was 17.769 ± 0.799 mg/g dry loquat leaf. HDES and TTAs were recovered from HDES extracting solution via gradient elution (60% and 80% ethanol aqueous solution, respectively) based on C18 reverse-phase silica gel column chromatography under low pressure (0.5 MPa). Recovered HDES could be reused for extracting TTAs from loquat leaves directly and had a similar extraction performance compared to fresh HDES. The purity of the obtained crude TTAs sample was 81.18% based on the total contents of maslinic acid (MA), corosolic acid (CA), oleanolic acid (OA) and ursolic acid (UA), with a mass ratio of 11:26:10:53. Crude TTAs sample was further separated by C18 reverse-phase silica gel column chromatography using 80% ethanol aqueous solution as mobile phase under high pressure (15 Mpa). By this mean, CA sample with 69.30% purity (MA to CA mass ratio 7:18) and UA sample with 93.94% purity (OA to UA mass ratio 4:21) were obtained. The in vitro antioxidant ability order of the attained TTAs samples was CA sample > crude TTAs sample > UA sample. This study laid a good scientific basis for applying HDES and C18 reverse-phase silica gel column chromatography in the bioactive component extraction and separation fields. It also provided theoretical basis and technical support for obtainment and utilization of high-purity loquat leaf TTAs in the fields of medicine, functional food, cosmetics and so on. •COSMO-SAC model prediction could be used to screen HDES for extracting TTAs.•Thy/BA demonstrated the highest loquat leaves TTAs extraction yield.•Crude TTAs and HDES were recovered via C18 low pressure chromatography.•CA sample and UA sample were separated by C18 high pressure chromatography.•Crude TTAs, CA sample and UA all have strong in Vitro Antioxidant Activity.