Chemical characterization and bioactivities of polysaccharides from Apocynum venetum leaves extracted by different solvents

Apocynum venetum has a long history as a Chinese traditional tea. As one of the major components, polysaccharides from Apocynum venetum leaves were extracted with acid (HCl), distilled water and alkaline (NaOH) to study the effect of the extraction solvents on their chemical composition and biological activities in this work. Monosaccharide composition revealed that polysaccharides from acidic and distilled water extraction were pectic polysaccharides, while those from alkaline extraction consisted of pectin and hemicellulose. Chemical analysis and FT-IR spectra indicated the co-extraction of protein and polyphenol contents in alkaline extracted polysaccharides, which exhibited strongest antioxidant and digestive enzyme inhibition activities. The antioxidant capacities were 185.26–286.30 mg TE/g for DPPH radical scavenging, 409.06–502.00 mg TE/g for ABTS radical scavenging, and 152.12–260.70 mg TE/g sample for reducing power assay, respectively. The lowest IC50 for α-glucosidase and lipase inhibition activities were 16.75 μg/mL and 820 μg/mL, respectively. Further purification of alkaline extracts was carried out and characterized. The results showed that acid hydrolysis could successfully reduce polyphenol and protein contents, and purified polysaccharides showed even higher antioxidant activities and α-glucosidase inhibition activity. These results provide a scientific support for functional application and extraction of polysaccharides from Apocynum venetum leaves.