Abstract
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.
Highlights
Astragalus L., the largest genus in the family of Leguminosae with approximately 2500–3000 species, is widely distributed throughout the temperate regions of the world[1]
One type of Response surface methodology (RSM), the Box-Behnken Design (BBD), has been widely used in the optimization of the extraction procedure because it dramatically reduces the number of experimental trails, saving time and decreasing expenses
Each technique has advantages, such as the easy accessibility and low cost of Hot air drying (HD), the vacuum environment, which prevents the oxidation reaction of polysaccharides during vacuum drying (VD), and the vacuum and freeze conditions, which protect the biological activities of polysaccharides during freeze drying (FD)
Summary
The ACPs yield did not significantly increase at the water to raw material ratio of 30 mL/g compared to 25 mL/g (P > 0.05). The reason for this might be due to the concentration difference between the Astragalus cicer L. tissue and the extraction solvent[9]. According to the single-factor experiment results, 17 runs of three variables were performed to determine the optimum extraction conditions for ACPs. The three variables were water to raw material ratio encoded as X1, extraction time encoded as X2 and extraction temperature encoded as X3.
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