Polysaccharides from Nitraria retusa Fruit: Extraction, Purification, Structural Characterization, and Antioxidant Activities

Abstract

Polysaccharides are important bioactive components of <i>Nitraria retusa</i> fruit (NRF). In this study, the ultrasonic-assisted extraction (UAE) conditions of polysaccharides from <i>Nitraria retusa</i> fruit (NRFPs) were optimized by response surface methodology (RSM). The structural characteristics and antioxidant activity were investigated. The maximum NRFPs yield of 3.35% was obtained under the following optimal conditions: temperature of 59.5 °C, time of 30.5 min, liquid-to-solid ratio of 19.5 mL/g. Three polysaccharide fractions, NRFP-1 (20.01 kDa), NRFP-2 (28.96 kDa), and NRFP-3 (67.45 kDa), were isolated. Glucose, galactose, and arabinose in different percentages were identified as the primary monosaccharide units. The Fourier transform infrared spectrometer (FT-IR) and nuclear magnetic resonance (NMR) analysis indicated the presence of α- and β-glycosidic bonds in NRFPs. The NRFP-3 exhibited the highest scavenging activities against DPPH, ABTS, -OH free radicals, and Fe⁺³-reducing activity.