Steam explosion pretreatment of Achyranthis bidentatae radix: Modified polysaccharide and its antioxidant activities

•Steam explosion pretreatment (SEP) enhanced extraction yield of polysaccharides.•Structural characteristics of polysaccharides were changed after SEP.•Steam-exploded polysaccharides presented better antioxidant activities. Steam explosion technology was employed for the pretreatment of Achyranthis bidentatae radix (ABR) under mild conditions, followed by the polysaccharide extraction. An increase in the extraction yield and uronic acid content of crude polysaccharide were detected, along with a decrease in the protein content induced by the steam explosion. The monosaccharide analysis showed the main compositional modification of polysaccharide is the increase in the proportion of galacturonic acid, galactose, and arabinose. It is consistent with the discriminant analysis of the FT-IR and UV–vis spectra. These structural modifications of crude polysaccharide caused by the steam explosion pretreatment (SEP) resulted in the significant increases in their antioxidant activities in vitro and in vivo. Strong correlations were observed between the pretreatment conditions and the changes in the structural characteristics and antioxidant activities of Achyranthis bidentatae radix polysaccharides (ABPS).