Rheological behaviors of ethanol-fractional polysaccharides from Dendrobium officinale in aqueous solution: Effects of concentration, temperature, pH, and metal ions

Ethanol fractional precipitation is an important technology to classify polysaccharides at different molecular weights. In this study, polysaccharides of Dendrobium officinale were step-precipitated by final ethanol concentrations of 40%, 60% and 80%, named as EPDO-40, EPDO-60 and EPDO-80, respectively. Chemical composition, molecule weights and monosaccharides were identified. Effects of concentration, temperature, pH and metal ions on rheological properties were investigated. Results showed that all EPDOs behaved as non-Newtonian fluid in a certain shear rate range of 0.1–1000 s−1 which is affected by their different chemical characteristics. Viscosities of all polysaccharides showed a concentration dependent manner, and they decreased with the increased temperatures from 10 to 90 °C. Viscosities of EPDO-40 and EPDO-80 increased at a range of lower pH significantly, while that of EPDO-60 decreased. Na+, K+, Mg2+ and Ca2+ could all affect the viscosity of EPDOs but in different patterns. Accordingly, it demonstrated that EPDOs with different chemical characteristics had different rheological properties, which could be applied more accurately in foods industry.