Ultrasound-assisted deep eutectic solvent extraction of polysaccharides from Melastoma dodecandrum: RSM optimization, ANN prediction, kinetics, structural characterization and cellular antioxidant activity.

Natural polysaccharides have attracted much attention due to their biocompatibility, biodegradability, low toxicity and various biological activities. However, the extraction of polysaccharides from Melastoma dodecandrum Lour. (MD) in a sustainable and effective way remains a challenge. In the present study ultrasound-assisted deep eutectic solvent (UA-DES) extraction strategy was developed to improve the yield and bioactivity of MD polysaccharides (MDPs). Among the twenty-five prepared DES systems, DES-3.2 (choline chloride:citric acid, 1:2) showed the best extraction performance. Response surface methodology (RSM) was applied for optimization of the extraction parameters and artificial neural network (ANN) model was established to predict the extraction behavior and performance. In addition, extraction kinetics was successfully described by second-order kinetic model. Under the optimized conditions of liquid-solid ratio of 30 mL/g, ultrasonic temperature of 60 °C, ultrasonic power of 360 W and ultrasonic time of 90 min, the MDPs yield reached 1.38 %, which was increased by 51.65 % compared with conventional HWE. Furthermore, ANN outperformed RSM in prediction accuracy and effectively captured the complex nonlinear interactions inherent to the extraction process. Structural characterization (SEM, FT-IR, XRD, HPGPC and TGA) analysis revealed that UA-DES extraction caused significant disruption of plant cell walls without changing the characteristic functional groups and amorphous structure of MDPs accompanied by higher molecular weight and thermal stability. Monosaccharide composition analysis identified galactose, galacturonic acid, and glucose as the predominant components with UA-DES extraction significantly enrich the galacturonic acid content compared with HWE. Further, UA-DES extracted MDPs had stronger antioxidant capacity in chemical assays and exerted higher antioxidant and anti-inflammatory effects in cells by significantly decreasing intracellular reactive oxygen species (ROS) and nitric oxide (NO) levels in LPS induced RAW264.7 macrophages without cytotoxicity. Additionally, DES-3.2 maintained over 91.25 % recovery after five recycling cycles, with only a 5.78 % loss in extraction efficiency of MDPs. Despite the modest absolute yield of 1.38 %, the excellent recyclability of DES-3.2 provides a strong economic counterbalance by reducing solvent costs and waste generation. Overall, UA-DES extraction is an effective, green, high-performance approach for extracting structurally distinct and bioactive MDPs for applications in functional foods, nutraceuticals and pharmaceuticals.