Effects of Removal of Metal Ions Bound to Lentinan on Its Structure and in Vivo Antioxidant Activity

Ethylenediaminetetraacetic acid disodium (EDTA-2Na) was used as a chelating agent to remove metal ions bound to lentinan (LNT). Changes in physicochemical properties, structure and antioxidant activity of LNT were studied after the removal of metal ions. The total sugar, protein and uronic acid contents were determined by the phenol-sulfuric acid method, Bradford’s method and the m-hydroxydiphenyl method, respectively. High performance gel permeation chromatography (HPGPC), ion chromatography (IC), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to determine the relative molecular mass, monosaccharide composition and advanced structure of LNT and demetallized LNT (dLNT), respectively. The in vivo antioxidant activities of LNT and dLNT were evaluated in mice. The results showed that after the removal of metal ions, the content of total sugar and uronic acid of LNT increased, the molecular mass range and distribution changed, and the composition but not proportion of monosaccharides remained unchanged. After metal ion removal, the surface structure became loose and the helical structure changed. Moreover, the antioxidant activity of dLNT in mouse serum was decreased compared with that of LNT. In summary, the removal of metal ions could destroy the structure of lentinan and weaken its antioxidant activity.