Chemical and rheological properties of polysaccharides from fruit body of Auricularia auricular-judae

Polysaccharide was extracted from Auricularia auricular-judae with hot water (AP). AP consisted mostly of carbohydrates (72%) and proteins (8%). The monosaccharide compositions mostly are Glucose (62%), Mannose (33%) and a small amount of Galactose (5%). The extracellular polysaccharide dispersions showed shear-thinning (pseudoplastic) behavior and its pseudoplasticity was more pronounced for 2% polysaccharide dispersion. The Power-law model was used to evaluate the viscosity curves of AP and both its viscosity and consistency indices changed as the concentration increased. The viscosity of polysaccharides dispersion decreased with the addition of salt and also at extreme pH values. AP dispersion behaved as a weak gel in the concentration of 0.5% and 1% and as a true gel at higher concentration (e.g, 2%). The addition of 1 M CaCl2 to AP and changing dispersion pH to acid or alkali decrease its gel strength. AP exhibited excellent thermal stability as assessed by rheology and DSC, suggesting the material could be used in food system which requires heat tolerance.