Extraction, purification, emulsifying property, hypoglycemic activity, and antioxidant activity of polysaccharides from comfrey

[Display omitted] •Hot water extraction method was used to extract polysaccharides from comfrey (CPs).•Response surface methodology (RSM) was used to optimize CPs extraction condition.•DEAE-52 cellulose and Sepharose CL-6B columns were applied to purify CPs.•The purified CPs possessed notable α-glucosidase inhibitory activity.•The purified CPs showed good antioxidant activity and emulsifying property Performing the researches on extraction conditions, purification and activities of polysaccharides are of great significance to the development of comfrey (Symphytum officinale L.) resources. In this study, the optimum extraction conditions of polysaccharides from comfrey (CPs) were obtained by response surface methodology (RSM), which were liquid to solid ratio 25 mL/g, extraction temperature 89 °C, and extraction time 155 min. A CPs yield of 19.20 % was obtained under these conditions. DEAE-52 cellulose and Sepharose CL-6B columns were used to purify CPs, and the purified polysaccharide component CPs-1.2 was obtained. The characteristics, emulsifying property, and hypoglycemic activity of CPs-1.2 were analyzed. The monosaccharide compositions of CPs-1.2 were galacturonic acid, arabinose, glucose, and galactose with the molar ratio of 1.00:0.88:2.28:1.13. CPs-1.2 showed notable DPPH and ABTS radical scavenging abilities, which could reach 95.00 % and 96.71 % of those of ascorbic acid at the determination concentrations of 0.4 mg/mL and 1.5 mg/mL, respectively. The α-glucosidase inhibitory activity of CPs-1.2 (10 mg/mL) could reach 80.00 % of that of acarbose. In addition, CPs-1.2 showed good emulsifying properties for olive oil, benzene, xylene and methylbenzene. These results suggested that CPs possessed potential as a hypoglycemic agent, an antioxidant or a polysaccharide-based emulsifier.