Physicochemical Characterization and Immunomodulatory Activity of a Novel Acid Polysaccharide from Solanum muricatum

To investigate the structure and immunomodulatory activity of polysaccharide from Solanum muricatum, a novel acid polysaccharide named SMP-3a was purified from Solanum muricatum pulp through DEAE-52 cellulose column and Sephadex G-200 chromatography. Monosaccharide composition analysis showed that SMP-3a was mainly composed of rhamnose, arabinose, galactose, and galacturonic acid with the molar ratio of 1.09:2.64:1.54:1. The average molecular weight was found to be 227 kDa by high performance gel permeation chromatography (HPGPC). Thermal studies revealed the SMP-3a was a thermally stable polymer. Based on the results of methylation and NMR analysis, the backbone chain of SMP-3a was composed of →2)-α-l-Rhap-(1→, →4)-α-d-GalpA-(1→ and →4)-α-d-Galp-(1→. The side chain was consisted of α-l-Araf-(1→ and →5)-α-l-Araf-(1→. Immunomodulatory assay indicated that SMP-3a could significantly promote the proliferation of macrophages and stimulate the secretion of cytokines, including TNF-α, IL-1β, and IL-6. Our results suggested that SMP-3a could be used as a novel potential immunomodulatory agent in functional food.