The isolation and characterization of polysaccharides from longan pulp

Crude water-soluble longan polysaccharides (LPSs) were extracted from longan pulp using hot water assisted by microwave pretreatment and ethanol precipitation. Neutral and acidic polysaccharides were separated by DEAE-cellulose anion-exchange chromatography. High performance gel permeation chromatography (HPGPC) analysis showed that the average molecular weight (Mw) of neutral polysaccharide (LPS-N) was approximately 13.8 kDa, and those of two acidic polysaccharides (LPS-A1 and LPS-A2) were approximately 1382 and 571 kDa, respectively. Structural properties and compositions of these three LPS were examined by FTIR and HPLC. It was hypothesized that LPS belong to β-type acidic heteropolysaccharides with pyran group, among which LPS-N was composed of xylose and glucose at the molar ratio of 1:1.9; LPS-A1 consisted of rhamnose, xylose, arabinose and galactose at the molar ratio of 1:1.64:4.33:2.28; and LPS-A2 comprised only rhamnose. The total uronic acid content of LPS-A1 and LPS-A2 were 6% and 19%, respectively.