Studies On Antioxidant Activity Of Polysaccharides From Dendrobium Candidum In Vitro

Dendrobium species as traditional Chinese herbs has been used for centuries. In many studies, polysaccharides from Dendrobii plants were found to be the main active components. In this paper, the total polysaccharide (DSP) was obtained from Dendrobium candidum, which was the top grade of Dendrobii, and then separated by ethanol to get different polysaccharide fractions. DSP and different polysaccharide fractions were determined to make sure the molecular weights and antioxidant activities, which would provid the basis for the application of Dendrobium candidum in medicine and food. The main results are as follows:1. Fractionation of DSP and determination of molecular weightsDSP was dissolved in deionised water and then continuously deposited by ethanol with final concentrations of 40%, 70% and 90% to obtain different polysaccharides fractions of DSP3, DSP2 and DSP1.Molecular weights of DSP, DSP1, DSP2 and DSP3, determined by gel chromatography method, were in the range of 1.57×10⁴-15.7×10⁴ Da, 1.48×10⁴ Da, 3.53×10⁴-7.44×10⁴ Da and 11.5×10⁴-15.7×10⁴ Da, respectively.2. Antioxidant activities of DSP and different polysaccharide fractionsThe antioxidant activities of DSP and different polysaccharide fractions were evaluated by O₂^-·, DPPH, chelating metal ions, anti-lipid peroxidation induced by Fe²⁺-V_C, ABTS, anti-erythrocyte hemolysis induced by H₂O₂ and DNA damage induced by·OH. Results showed that different polysaccharide fractions had strong antioxidant activities in dose-dependent manner in all assays except O₂^-·. DSP1 exhibited strongest antioxidant activities among polysaccharide fractions in DPPH-scavenging activity, reducing power, anti-lipid peroxidation induced by Fe²⁺-V_C, ABTS-scavenging activity and anti-erythrocyte hemolysis induced by H₂O₂. DSP had better antioxidant activities than others in·OH-scavenging activity and chelating metal ions. DSP3 showed better scavenging activities on H₂O₂ radical and NO radical than others. All the polysaccharide fractions showed excellent protection effect on DNA damage induced by·OH.In conclusion, 4 polysaccharide fractions of D. candidum exhibited different antioxidant activities, which were possibly related with molecular weight and the construction of polysaccharides.