Abstract
The network structure of high acyl gellan polysaccharide was investigated using dynamic viscoelasticity and steady flow viscosity measurements, as well as atomic force microscopy (AFM). Time-temperature superposition (TTS) of mechanical spectra of aqueous dispersions having a gellan concentration of 0.1% w/w revealed a gel-like response at the lower end of the frequency range. The TTS master curve of the steady flow data exhibited a power-law relationship between shear viscosity and shear rate at the lower end of the shear rate range, instead of a Newtonian plateau. These rheological characteristics suggest the existence of an effective yield stress arising from the presence of a percolated network. AFM images of high acyl gellan revealed micrometer-sized networks composed of double-stranded helices laterally associated to varying degrees. These associated helices did not dissociate fully on heating at 90°C, suggesting that they are partially preserved native networks secreted by gellan-producing bacteria.
