Ultrasonic-assisted extraction, structural analysis and antioxidative mechanism of polysaccharide from sunflower disc

The crude sunflower disc polysaccharide (SDP) was obtained by using ultrasonic assist hot water extraction. Homogeneous SDP was separated by DEAE-cellulose column and Sephacryl S-400 HR column. Its physical properties and antioxidant mechanism was studied. Results showed that extraction yield of SDP was 15.3 %, total sugar was 91.3 %, weight molecular weight (Mw) was7.46 x 103 Da, number-average molecular weight (Mn) was 6.16 x 103 Da and polydispersion coefficient (Mw/Mn) was 1.21. SDP was composed of galactose (Gal), fucose (Fuc), xylose (Xyl), glucose (Glc), arabinose (Ara), rhamnose (Rha), glucuronic acid (Gle-UA) and galacturonic acid (Ga-UA), and the ratio of substance were 1.77:2.00:4.55:8.44:9.57:14.26:2.13:57.28. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results showed that smooth surface and structure of SDP was relatively dense, and some crystallization existed, but the crystallization was weak. Two-dimensional structure of SDP showed that the main chain -*4)-alpha-d-GalpA-(1-*, -*3)-alpha-l-Araf-(1-*, -*2)-alpha-l-Rhap-(1-*, -*2, 4)-alpha-l-Rhap-(1-*, -*2, 4)-alpha-d-GlcpA-(1-* and -*3, 6)-beta-d-Galp-(1-* interconnection form. Results of in vitro and in vivo of SDP and its derivatives showed that a good antioxidant activity. In vitro antioxidant activity, the scavenging rates of ABTS+, & sdot;OH, DPPH and superoxide anions were 95.8 %, 93.9%, 93.6% and 92.1 %, respectively, when treated with 3.2 mg/mL of SDP solution. The preliminary antioxidative mechanism results showed that SDP had a regulatory effects on the down-regulation of Nrf2, HO-1 and NQO1 proteins in RAW264.7 cells. Preliminary pharmacokinetic analysis showed that the SDP could be absorbed orally and reached its peak concentration in the blood at about 2 h. The content of polysaccharide in blood reached the peak value at 30 min and reached the lowest value at 8 h after intravenous injection.