Fractionation, structural characteristics and immunomodulatory activity of polysaccharide fractions from asparagus (Asparagus officinalis L.) skin

The physicochemical properties, structural features and structure-immunomodulatory activity relationship of pectic polysaccharides from the white asparagus (Asparagus officinalis L.) skin were systematically studied. Using sequential ethanol precipitation, five sub-fractions namely WASP-40, WASP-50, WASP-60, WASP-70 and WASP-80 with distinct degree of esterification (DE) and molecular weight (Mw) were obtained. The Mw and DE values were decreased with the increase of the ethanol concentrations. Structurally, although 4-α-D-GalpA was the dominant sugar residue in all fractions, the molar ratios were decreased, whereas other sugar residues including arabinose- and mannose-based sugar residues overall increased with the increase of ethanol concentration. In addition, the effects of sub-fractions on the RAW 264.7 cells indicated that pectic polysaccharides with the higher DE value showed a stronger immunomodulatory activity. Moreover, the structure-activity relationship was also discussed in this study, which extends the value-added application of asparagus and its processing by-products.