Ultrasound-assisted ethanol/K2HPO4 aqueous two-phase extraction of polysaccharides from Plantago asiatica L. seeds: Process optimization, physicochemical properties, and antioxidant activity.

Abstract

The seeds of Plantago asiatica L., a folk herb, are rich in polysaccharides that possess antioxidant, antidiabetic, and anti-inflammatory properties. Polysaccharides with lower molecular weights generally exhibit higher biological activity, so a method to efficiently extract low-molecular-weight polysaccharides from P. asiatica L. seeds (PLPs) is needed. The aim was to establish an efficient method for extracting polysaccharides from P. asiatica L. seeds while preserving their activity. Response surface methodology was applied to determine the optimal polysaccharide extraction conditions. Subsequently, the extracted polysaccharides were characterized to determine their monosaccharide composition, physicochemical properties, and molecular weight. Their antioxidant activity was evaluated by measuring their ability to scavenge DPPH and ABTS free radicals. An extraction yield of 9.17% was achieved under an ethanol concentration of 18.0% (w/w), a K2HPO4 concentration of 27.8% (w/w), a solvent-to-material ratio of 30:1 (mL/g), an ultrasound power of 203 W, and an extraction time of 39 min. Structural analyses indicated that this method might cause physicochemical changes in the conformation of PLPs and induce the degradation of PLP side chains but not the backbone. The antioxidant assay results showed that the DPPH and ABTS radical scavenging rates of PLPs were 48.3% and 49.2%, respectively, while in the control group the radical scavenging rates were 35.5% and 37.1%, respectively. The established method for extracting polysaccharides from P. asiatica L. seeds is efficient and reliable. The polysaccharides could be used as an important resource with antioxidant activity.