Optimization Extraction Process of Polysaccharide from the Pericarp Residues of Euryale ferox and Its Antioxidant Activity in Vitro

In order to realize the high value utilization of the by-products from the processing of Euryale ferox, the optimal extraction technology parameters of polysaccharides from the pericarp residue of Euryale ferox were obtained, the physical and chemical properties were analyzed, and the antioxidant activity of polysaccharides was preliminary studied by the in vitro scavenging free radical test. Based on the single factor tests, the material-liquid ratio, extraction temperature, extraction time, and alcohol concentration were selected as independent variables, and the polysaccharide yield was the dependent variable. The L₉ (3⁴) orthogonal test method was used to optimize the extraction process of polysaccharides. Using five antioxidant activity test methods in vitro, namely total reducing power, scavenging hydroxyl free radicals, DPPH free radicals, superoxide anion and nitrites, and comparing them with ascorbic acid, the antioxidant properties of polysaccharides were evaluated ability. The results showed that the optimal extraction process was a ratio of material to liquid of 1:40, an extraction temperature of 55℃, extraction 40 min, alcohol precipitation concentration 80%, and three extractions with an extraction rate of 45.94%and a purity of 82.67%. The iodine-potassium iodide reaction showed that the polysaccharide was a non-starch polysaccharide, and HPLC analysis of the hydrolysate showed that its basic structural unit was glucose. The water absorption and oil absorption of polysaccharides were (65.15±1.52) and (1.27±0.04) g/g respectively. The texture properties of the polysaccharide gel showed that it had great viscosity, low elasticity and weak recovery ability. The polysaccharides had good scavenging ability to hydroxyl free radicals, DPPH free radicals, superoxide ions and nitrites. When the concentration of polysaccharides was 1.0 mg/mL, the scavenging rates for hydroxyl free radicals, superoxide ions and nitrite were 35.56%, 34.88% and 20.63%, respectively, and the IC₅₀ for DPPH free radical scavenging rate was (0.307±0.008) mg/mL. The optimal extraction process of polysaccharides from the Euryale ferox pericarp residues were stable and reliable, and the polysaccharides had certain antioxidant capacity. The test results would provide theoretical basis for the comprehensive development and utilization of the processing by-product resources of Euryale ferox.