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Litchi polysaccharide (LP) was extracted from litchi pulp. Its chemical composition, microstructure, zeta potential, flow and viscoelastic behavior were investigated. LP contained uronic acid (41.18%), neutral sugar (42.23%), and protein (2.72%). The monosaccharide composition was mostly arabinose, galactose, and a small amount of mannose, rhamnose and glucose. Scanning electron microscopy (SEM) showed LP was porous network structure. LP concentration had no effect on its zeta potential value while salts reduced them. LP showed shear-thinning behavior during the tested shear rate range. The power-law model was used to evaluate the flow behavior of LP; both its flow behavior index and consistency index changed with different concentrations. The viscosity of LP increased under acidic conditions (pH2-4), but was stable with heat treatment. The LP dispersion displayed as a liquid viscoelastic behavior in 1% and 2% concentrations and behaved as an elastic gel at 3% concentration as well as the addition of NaCl and CaCl 2 ., (Copyright © 2018. Published by Elsevier B.V.)

Three water-soluble hetero-polysaccharides, designated LP1-3, were isolated from litchi pulp. Their structures, solution properties and immunomodulatory activities were evaluated. LP1 contained (1→4,6)-β-d-Glc and (1→4)-α-l-Gal, while LP2 contained (1→3)-α-l-Ara and (l→2)-β-d-Gal, and LP3 contained α-l-Ara and (l→4)-β-Rha. Their molecular weights ranged from 105,880 to 986,470g/mol. LP1 had a spherical conformation with hyper-branched structure and LP2 was semi-flexible chain, while the polysaccharide chains of LP3 were cross linked to form network-like conformation in solution. In addition, all fractions strongly stimulated mesenteric lymph node cell proliferation, IFN-γ and IL-6 secretion in the dose range of 25-100μg/mL compared with untreated control group (p<0.05). LP1 exhibited the strongest stimulation of mesenteric lymph node cell proliferation and cytokine secretion, which may be attributed to its unique chemical structure and chain conformation. This is the first report on the solution properties and intestinal immunity activities of polysaccharides from litchi pulp., (Copyright © 2016 Elsevier Ltd. All rights reserved.)