Optimization of Ultrasound‐Assisted Water Solvent Extraction and Bioactivities of Polysaccharide From <i>Eleusine indica</i> (L.) Gaertn

ABSTRACT To contribute to the development of natural plants in the field of medicine, the study investigates optimization of the best process of extracting polysaccharides of Eleusine indica (L.) Gaertn polysaccharide (EIGP) with water as a solvent and the bioactivity of EIGP in vitro. EIGPs were extracted by an ultrasonic‐assisted method using water as a solvent; a one‐factor experiment was carried out first, and then a response surface experiment was designed according to the four‐factor and three‐level design by using the Design‐Expert software. The polysaccharide extract of Eleusine indica (L.) Gaertn (EIG) was eluted with a DEAE column and Sephadex G‐75 column to obtain the purity of polysaccharides. The purified polysaccharide was then subjected to preliminary antioxidant and hypoglycemic activities by enzyme inhibition and in vitro free radical scavenging assays. The optimal extraction conditions were ultrasonic power of 240 W, solid–liquid ratio of 1:17 g/mL, time of 31 min, and temperature of 50°C, under which the polysaccharide extraction rate of EIG was 11.50% and the purity was 73.45%. In the bioactivity study of polysaccharides, the results were as follows: in the α‐glucosidase inhibitory activity assay, the IC 50 of these polysaccharides and acarbose were measured to be 59.84 and 4.4 × 10 −4 mg/mL, respectively; in the α‐amylase inhibitory activity assay, the IC 50 of these polysaccharides and acarbose were measured to be 59.98 and 0.2173 mg/mL; in the DPPH• radical scavenging activity assay, the IC 50 of the polysaccharide and Vitamin C (VitC) were measured to be 43.95 and 0.0126 mg/mL, respectively; in the ABTS• + scavenging assay, the IC 50 of the polysaccharide and VitC were measured to be 0.4188 and 0.004 mg/mL, respectively. In this thesis, the process of extracting polysaccharides from EIG with water as a solvent was investigated and optimized. The bioactivity study experiments showed that EIGPs‐1, purified from EIG, have certain antioxidant and hypoglycemic activity.