| Summary: | This paper studies the optimization of ultrasonic-assisted extraction of polysaccharides from Oenothera biennis L. leaves using Box-Behnken design, and their in vitro antioxidant activity and structure. It is demonstrated that the optimum extraction conditions are: the ultrasonic power at 400 W, solvent-tosample ratio of 23:1 (mL/g), ultrasonication temperature at 53 °C, and time for 36 min, under which the yield of polysaccharides from Oenothera biennis L. leaves, namely 3.54%, remains close to the predicted value in the model. The assays of the scavenging effect on DPPH and hydroxyl free radicals, and of the reducing power indicate that polysaccharides from Oenothera biennis L. leaves possess strong antioxidant activity and certain relationship exists between their dose and effect in the concentration range of the experiment; Fourier IR spectroscopy reveals that characteristic absorption peak of polysaccharides can be seen from the sample; the DE-52 cellulose column chromatography, HPLC profiles, and GC-MS chromatogram identify the obtained OCP-2 as heteropolysaccharides, whose major components, including arabinose, mannose, galactose, and talose, have an average molecular weight of 5435 Da.
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