Optimization of Process of Hydrolysis of Dendrobium officinale Polysaccharide and Determination of Contents of Its Mannose

Process of hydrolysis of Dendrobium officinale polysaccharide by high temperature and pressure-sulfuric acid assisted was optimized by response surface method (RSM) according to Central Composite Design (CCD), and polysaccharides of Dendrobium officinale under the conditions of different cultivation were determined by phenol-sulfuric acid method, and the contents of mannose from different parts (stems, leaves and flowers) of Dendrobium officinale were analyzed by pre-column derivation HPLC method. The research showed that the optimum parameters was as follow: Material-liquid ratio was 1:1.5 (mg/mL), concentrations of sulfuric acid was 1 mol/L, hydrolysis temperature was 112 ℃ (0.15 MPa) and hydrolysis time was 44 min. Under optimal conditions, the content of the mannose was 64.35%±0.76% with stem as the test material. The contents of polysaccharide in stems, leaves and flowers of Dendrobium officinale under the conditions of same cultivation were significantly differences (P<0.01, stems>leaves>flowers). And the contents of mannose in the samples was the same as that of polysaccharide. The content of polysaccharide and mannose in the stems were 29.32%~33.78% or 18.17%~21.05%, respectively. And the contents of polysaccharide and mannose in the leaves were 15.91%~17.31% or 10.28%~11.11%, respectively. And the contents of polysaccharide and mannose in the flowers were 8.37%~8.68% or 5.30%~5.75%, respectively. The results indicated that the method was effective and efficient, which could be used for the hydrolysis of Dendrobium officinale polysaccharide by high temperature and pressure-sulfuric acid assisted. And the stems, leaves and flowers of Dendrobium officinale were high-quality natural resources for the preparation of mannose.