Ultrasound-assisted deep eutectic solvent extraction of flavonoids from pericarp of cultivated 'Qi-nan' agarwood: identification, optimization, and antioxidant activity

With the expansion of the cultivation area of 'Qi-nan' species, the amount of fruit resources has increased correspondingly. However, each felling for agarwood results in many 'Qi-nan' fruits being discarded, resulting in significant resource waste. To investigate the chemical constituents of 'Qi-nan' fruits and improve the utilization of their resources, this study employed ultrasound-assisted deep eutectic solvent extraction (UA-DES) to extract flavonoids from the 'Qi-nan' pericarp(FQP). First, 13 flavonoids, including quercetin, and kaempferol, were identified from the 'Qi-nan' pericarp using ultra-performance liquid chromatography-mass spectrometry (UPLCMS). Next, the highest yield of FQP reached 12.03 f 0.24 %, significantly higher than that obtained with 50 % ethanol, and enhanced by 1.44 times, using a molar ratio of 1:2 choline chloride/urea(ChCl/urea (1:2)) as the optimal solvent, a 40 % water content, a 30 mL/g liquid-to-solid ratio, 40 min ultrasonication time. Additionally, scanning electron microscopy (SEM) indicated that the treatment with ChCl/urea (1:2) caused greater destruction of the sample compared to traditional solvent ethanol. The antioxidant activity indicated that the IC50 values of ChCl/urea (1:2) against DPPH and ABTS+ radicals were 30.66 f 0.36 and 47.13 f 0.79 mu g/mL, respectively, while those of ethanol extracts were 37.23 f 0.13 and 48.08 f 0.15 mu g/mL. The FRAP slopes for ChCl/urea (1:2) extract and ethanol extract were 0.2216 and 0.1835, respectively. This suggests that UA-DES is a more efficient and active method for extracting FQP than conventional solvent extraction. This study provides data support to the development and use of the 'Qi-nan' pericarp, along with a sustainable efficient method for the extraction of FQP.