International Journal of Medicinal Mushrooms

The Effects of Temperature, pH, and Cations on the Rheological Properties of the Extracellular Polysaccharides of Medicinal Species of Genus Tremella Pers. (Heterobasidiomycetes)

ABSTRACT

Extracellular polysaccharides were produced from nine Tremella species using the malt-yeast (MY) media. The rheological properties of the polysaccharide solution were examined by the Power-law model. The extracellular polysaccharide solutions showed shear-thinning (pseudoplastic) behavior. The pseudoplasticity was more pronounced for 5% polysaccharide solutions. T. cinnabarina and T. indecorata polysaccharide solutions (0.1% w/v) gave the highest and lowest viscosities—9.18 and 1.73 mPa, respectively—at 25°C and at a shear rate of 150 s⁻¹. The effects of chemical and physical factors on solution viscosity were studied. The viscosity of solutions decreased with an increase in temperature and also at extreme pH values. Rheological analysis revealed that divalent cations (calcium and zinc) did not increase the viscosity of polysaccharides, but monovalent cations (sodium and potassium) did, which suggests that ionic bridging occurred between polymer chains. A synergistic increase in the viscosity of the solution was observed when the polysaccharides were mixed with xanthan.