Rheological properties of water-soluble spruce O-acetyl galactoglucomannans

The thermal and rheological properties of spray-dried, ethanol-precipitated, purified, and deacetylated spruce galactoglucomannans (GGM) were investigated by rheological measurements and differential scanning calorimetry. The shear rate dependence of viscosity and the effects of the drying method, temperature, ionic strength, and deacetylation on rheological properties were studied. GGM solutions exhibited a shear thinning behaviour. GGM solutions did not obey the Cox–Merz rule. The storage modulus of GGM solutions increased with an increase in concentration; gradually until a concentration of 5%, but rapidly at higher concentrations. Ethanol-precipitated GGM solutions showed a more elastic behaviour than spray-dried GGM solutions. Deacetylation caused an increase in apparent viscosity and more significantly in storage modulus. The storage modulus increased slightly with a decrease in temperature. A small amount addition of NaCl slightly changed the oscillatory behaviour. The effects of above factors were discussed in terms of molecular interactions. The rheological measurements of GGM solutions provide the basis of functionalities of GGM solutions.