Isolation and purification, structure identification and antioxidant activity of Monascus purpureus exopolysaccharide

Objective: To isolate and purify the crude Monascus purpureus exopolysaccharide (EPS) and study the structure identification and antioxidant activity of the exopolysaccharide fractions. Method: The crude polysaccharide was extracted by liquid fermentation and purified by DEAE-cellulose.Molecular weights (Mw) of exopolysaccharide fractions were determined by high performance gel permeation chromatography (HPGPC) and the monosaccharide compositions were determined then by HPLC using precolumnderivatization with 3-methyl-1-phenyl-5-pyrazolone (PMP) separately.The ability of scavenging DPPH and hydroxyl free radical of polysaccharide fractions was tested to evaluate the antioxidant activity. The findings showed that three fractions (EPS-1, EPS-2, EPS-3) were obtained and molecular weights (Mw) were 8673, 143537, 238742 Da respectively.Both EPS-1, EPS-2 were composed of mannose, rhamnose, glucose and galactose with a molar ratio of1∶ 0.301∶ 2.052∶ 3.614 and 1∶ 2.475∶ 1.950∶ 1.532, EPS-3 were composed of mannose, rhamnose, Glucuronic acid, glucose and galactose in a molar ratio of 1 ∶ 0.401 ∶ 0.066 ∶ 0.307 ∶ 2.974. The ability of removing DPPH and hydroxyl free radicals of polysaccharide fractions were positively related with concentrations. When it was up to 1 mg/m L, the DPPH clearance rate turned out to be 16.4%, 15.9% and 14.8% respectively, hydroxyl free radical clearance rate of EPS-3 was 63.8%, and EPS-1, EPS-2 was 40.4% and 39.6% respectively. Conclusion: There existed some difference in monosaccharide composition and relative molecular mass and the ability of scavenging hydroxyl free radical and DPPH scavenging ability among EPSs, which could be associated with Mw and their structures.