Rheological Properties Of Konjac Glucomannan/curdlan Sol

Konjac glucomannan(KGM) is a natural polysaccharide with gelling, thickening, and film-forming abilities. It is widely used in dairy products, beverages, and edible films. Curdlan is an extracellular polysaccharide produced by microbial fermentation, it has a high thermal stability, resistance to freezing and thawing characteristics, and widely used in food preparation. KGM and Curdlan blended sols exhibits special viscous-elastic and gel properties. Understanding these properties and their molecular mechanism are the basis for its application in the food industry. In this study, the mainly results are following:1. The experimental data for the shear viscosity and shear rate curve of KGM sol was fitted to Cross-model equation:. Shear thinning of KGM sol occurred in the concentration range of 0.1 to 1.0%, and this sol was defined as pseudoplastic fluid. The apparent viscosity of KGM sol decreased with increasing temperature in the concentration of 0.5 to 1.0%. The experimental data for the apparent viscosity and temperature curve was fitted to Arrhenius equation:. The viscous flow activation energy of 0.5% KGM, 0.7% KGM, and 1.0% KGM were 3.28 ± 0.047, 8.96 ± 0.115, and 19.67 ± 0.062 kJ/mol, respectively. Dynamic frequency scan showed that KGM sol was mainly viscous in the low frequency region, and elastic in the high frequency region.2. AFM and TEM images showed that curdlan existed as micelles at 25-40 oC. It hydrated with the increasing temperatures and dissociated into microfibrils, the length of these microfibrils was 270 nm and the height was between 1 to 3 nm at 50-70 oC. When curdlan was heated at 75-90 oC, curdlan molecules dissociated into smaller microfibrils, its molecular chain length is 90 nm and height is 1-2 nm, it is a single helical chain. Rheological experiments showed that the curdlan water dispersion can form a low-set gel at 50-60 oC. When the temperature increased to 80 oC or above, it can form a high-set gel. The transition temperature is 40 oC on heating in water then cooling. It maybe involved hydrogen-bond interactions between curdlan molecules which lead to the rearrangement of curdlan melecules.3. Blending KGM with curdlan had viscosification compared to pure KGM and pure curdlan sol at 90 oC. The collaborative stress index increased from 1.43 to 1.97 as their ratios increased from 1:1 to 1:2. Micro DSC analysis showed that the enthalpy of mixing sol(△Hmix) is less than the enthalpy of sum sol(△Hsum), suggesting that KGM molecular chain impacted aggregative behavior of curdlan molecules in the cooling process. This result was consistent with the result of the rheological temperature scanning. KGM and curdlan formed interpenetrating network structure when the solution cooled from 90 to 25°C.