Ultrasound-assisted deep eutectic solvent extraction of ginseng folium polysaccharides: Extraction mechanism, process optimization, structural characterization, and in vitro biological activity

This study aimed to develop a green, efficient ultrasound-assisted (UA) deep eutectic solvent (DES) extraction method for ginseng folium polysaccharides (GFPs). This approach overcomes the low yields and long extraction period of conventional techniques. Seventeen DES systems were screened, identifying choline chloride-lactic acid (ChCl-La, 1:2) as the optimal solvent. Key parameters were optimized using Plackett-Burman design followed by Box-Behnken response surface methodology, yielding optimal conditions of 30 min ultrasonic time, a liquid solid ratio of 25 mL/g, ultrasonic power of 299.16 W, and DES water content of 30.82%. The effects of three extraction methods, namely hot water extraction (HWE), UA extraction (UAE), and UA-DES, on polysaccharide characteristics were compared. Monosaccharide analysis showed that HWE-GFP was rich in glucose (Glc, 16.15%) and glucuronic acid (GlcA, 45.23%), whereas UAE and UA-DES were enriched in galactose (30.79% and 37.78%, respectively) and arabinose (21.69% and 29.80%, respectively). UA-DES-GFP had a significantly lower molecular weight (361.70 kDa) than UAE-GFP (1497.40 kDa) or HWE-GFP (3304.35 kDa). Fourier-transform infrared spectroscopy revealed no major differences in functional groups among the three GFPs. Molecular dynamics simulations of the ChCl-La system elucidated the extraction mechanism, highlighting favorable electrostatic potential energy (-20.14 eV) and hydrogen bond length (2.204 Å) interactions with GFP. In vitro bioassays showed that HWE-GFP had stronger antioxidant activity (61.97%), whereas UA-DES-GFP exhibited superior α-glucosidase inhibition (59.54%). These differences likely stem from variations in the GlcA/Glc ratio. Overall, this study provides a high-yield, green extraction strategy for GFP, along with mechanistic insights and technical guidance for utilizing ginseng leaf polysaccharides.