Purification, preliminary structural characterization and in vitro antioxidant activity of polysaccharides from Acanthus ilicifolius

• Two polysaccharides were isolated from A. ilicifolius, named as NAIP and AAIP-B.
• NAIP was a neutral polysaccharide, of which the molecular weight and the structure properties were determined.
• AAIP-B was determined to be an acid pectin-type polysaccharide.
• AAIP-B was the most effective antioxidant in CAIP.

Crude Acanthus ilicifolius (A. ilicifolius) polysaccharides (CAIP) were obtained by hot water extraction and deproteinated. Two major polysaccharide fractions, the neutral A. ilicifolius polysaccharide (NAIP) and the acid A. ilicifolius polysaccharide B (AAIP-B), were isolated from CAIP by chromatography using DEAE-Sepharose Fast Flow and Sepharose CL-6B. The molecular weights (Mw) of NAIP and AAIP-B, determined by high performance gel-filtration chromatography (HPGFC), were 11,775 and 23,161 Da, respectively. AAIP-B contained 51.23% uronic acid, characteristic of a pectin-type hetero-polysaccharide. Analysis of the neutral monosaccharide composition indicated that NAIP contained high proportions of arabinose, galactose and glucose. However, AAIP-B was mainly composed of rhamnose, arabinose and galactose. Their structure properties were confirmed by FT-IR.Both CAIP and AAIP-B had good free radical-scavenging capacities and reducing powers. AAIP-B was the most effective antioxidant in CAIP. AAIP-B (0.2 mg/mL) could scavenge 80% of DPPH free radicals and 56.4% of superoxide anion radicals.