Extraction condition optimization and effects of drying methods on physicochemical properties and antioxidant activities of polysaccharides from Astragalus cicer L.

Response surface methodology (RSM) including three variables was performed to optimize the extraction parameters of Astragalus cicer L. polysaccharides (ACPs). The influence of different drying techniques on the physicochemical properties and antioxidant abilities of ACPs were evaluated. The ACPs were dried with hot air (HD), vacuum (VD) and freeze drying (FD) methods. The optimal conditions for ACPs extraction were as follows: water to raw material ratio of 25 mL/g, extraction time of 61 min and temperature of 75 °C. Under these parameters, an ACPs yield of 10.97% was obtained. HPLC analysis showed that the monosaccharide compositions of the three ACPs dried with HD, VD or FD techniques were identical. The three ACPs exhibited antioxidant abilities in a concentration-dependent manner. ACPs dried with the FD method (FD-ACPs) had the best antioxidant activities, which might be related to their smaller molecular weight and higher uronic acid content. At the determined concentration of 1 mg/mL, the ferric reducing power, and DPPH and ABTS free radical scavenging capacities of FD-ACPs were 0.762, 75.30% and 99.21%, respectively. Therefore, FD was a good choice for the drying of Astragalus cicer L. polysaccharides.