Discussion
In conclusion, these results imply that the ChCl:Oa-UAE method might be an environmentally friendly approach for extracting EA from GJ.
Methods
NADES with the highest EA yield was selected and the extraction conditions were optimized by response surface methodology (RSM), the antioxidant activity of NADES extract was determined, and finally Fourier transform infrared (FT-IR) and scanning electron microscopy (SEM) were used to explain the mechanism for the increase of EA yield in GJ.
Results
In this work, several NADESs were tailored for the ultrasound assisted extraction (UAE) of EA from GJ, among which choline chloride-oxalic acid (ChCl:Oa) was the most effective. In optimal conditions, ChCl:Oa extract produced higher EA yields than common organic solvents including methanol, ethanol, and acetone. In vitro antioxidant experiments showed that ChCl:Oa extract had stronger DPPH radical scavenging ability than other solvent extracts. Mechanically, FT-IR results indicated that ChCl:Oa could form a hydrogen bonding with EA, which enhanced the stability of EA. Meanwhile, ChCl:Oa-UAE treatment could destroy the tissue structure of GJ, thereby improving EA yield.