Structure characterization of two novel polysaccharides from Colocasia esculenta (taro) and a comparative study of their immunomodulatory activities

Two fractions of non-starch polysaccharides termed TPS-1 and TPS-2 were sequentially purified from the corms of Colocasia esculenta. Structural characterizations of TPS-1 and TPS-2 were determined. The average molecular weight of TPS-1 and TPS-2 were estimated to be 10.502 and 10.191 kDa, respectively. TPS-1 consisted of Rha (8.5%), Xyl (0.73%), Glc (88.57%), and Gal (2.56%), while TPS-2 consisted of Rha (3.54%), Arf (1.6%), Glc (87.92%), and Gal (6.94%). The presence of glycosidic linkages in the two fractions of polysaccharides were identified and were significantly different. TPS-2 exhibited a higher immunomodulatory activity than TPS-1 through an immunostimulation assay promoting NO, TNF-α, and IL-6 production in RAW 264.7 cells. Furthermore, TPS-2 could significantly enhance the phagocytosis ability of macrophages. The membrane receptors of TPS-2 were identified to be TLR2, TLR4, GR, and SR. Taken together, TPS-1 and TPS-2 could be considered as novel potential immunostimulants of food and pharmaceutical supplements for hypoimmunity.