Rheological and physicochemical properties of polysaccharides extracted from stems of Dendrobium officinale

The physicochemical and rheological properties of polysaccharides extracted from stems of Dendrobium officinale (DOP) were investigated. Two samples were prepared: the first sample (HEPDOP) was prepared by pretreating D. officinale stems by hot water scalding, followed by water extraction and ethanol precipitation; and the second sample (EPDOP) was obtained by water extraction and ethanol precipitation without pretreatment. The contents of total carbohydrate and protein, mannanase activity, infrared spectra, molecular weight distribution, thermal properties, and hydrophobicity of the two samples were analyzed. The results showed that mannanase activity of HEPDOP (0.0247 U) was much lower than that of EPDOP (0.1158 U). HEPDOP had higher molecular weight and carbohydrate content, and lower polydispersity index (PDI) value and protein content compared to EPDOP. The results further showed that the decomposition temperature of HEPDOP was 311 °C, which is higher than that of EPDOP (306 °C); and its hydrophobicity was significantly lower than that of EPDOP. Interestingly, at the same concentration (2% (w/w)), HEPDOP had higher viscosity than EPDOP, and acidity, alkalinity, the addition of salt ions, and temperature was found to reduce their viscosity. Finally, we observed that increasing temperature caused the decrease of viscosity and modulus of both DOPs.