Rheology of triple helical Lentinan in solution: Steady shear viscosity and dynamic oscillatory behavior

The steady shear viscosity and dynamic oscillatory behaviors of triple helical Lentinan, a β-(1→3)-d-glucan from Lentinus edodes, in water at 25 °C were studied by Rheometric Scientific ARES-controlled strain rheometer. The intrinsic viscosity was measured by Ubbelohde viscometer and estimated to be 903.3 mL/g from the intercept of the linear plot of ηsp/c vs. ηsp. As found for normal disordered polysaccharides, shear-thinning behavior was observed. But a peculiarity is that the shear-thinning behavior occurred at lower concentration and very low critical shear rate. The zero shear viscosity (η0) and specific viscosity (ηsp) increased with an increase of polymer concentration and degree of space occupancy (c[η]), respectively, similar to the general trend of most disordered polysaccharides. The critical concentration c*, at which the transition from a dilute solution of independently moving chains to a network occurred, was determined to be about 3.8×10−4 g/mL, which was much lower than that of general disordered polymers. This may be attributable to the nature of stiffness of triple helical Lentinan. The results from dynamic experiments revealed that Lentinan in pure water could form cross-linked network structure and weak gels with increasing polysaccharide concentration.