Optimization and antioxidant activity of polysaccharides from Plantago depressa

•Extraction yield of PDP was optimized by response surface methodology.•PDP was characterized by HPLC-MS and IR.•PDP exhibited strong radical scavenging and β-carotene bleaching protection activities.•PDP could be considered as safe bioactive agents.

Polysaccharide from the herb of Plantago depressa (PDP) was obtained through ethanol precipitation preceded by a water extraction step. The optimum extraction yield of 5.68 ± 0.46% was obtained with the treatment of raw material in water (w/v, 1:25.34) at 80.44 °C during 1.97 h, 3.28 times. Under these conditions, obtained yield value was in total agreement with value predicted by the model executed by Box-Behnken design (BBD). Following analysis by IR, HPLC-UV, MS and 1H NMR, the composition of PDP was found to be l-rhamnose, galactose, arabinose, glucose and d-galacturonic acid. The maximum tolerated dose of PDP was 10 g/kg. The antioxidant activity of PDP was investigated using five tests and it was found that PDP was able to scavenge hydroxyl, DPPH and ABTS radicals, besides their β-carotene bleaching inhibitory activity. In particular, in the test of β-carotene bleaching inhibition, PDP displayed higher activity than Vitamin C.