Phase and rheological behaviors of xanthan/amylose and xanthan/starch mixed systems

Phase separation and rheological properties of wheat starch (2 wt%) or amylose (0.3 wt%) with xanthan (0.1 or 0.5 wt%) mixtures were investigated at two salt levels (less than 0.01 M equivalent NaCl and 0.1 M NaCl). Mixed systems were prepared with pre-heated solutions and/or dispersions. Appearance of two or more phases upon time, followed using a technique based on multiple light scattering, occurred at both salt concentrations. However, it was faster and more pronounced at higher salt concentration. Generally, a transparent upper phase, an intermediate diffuse turbid zone (amylose aggregates) and an opaque down phase (granules and/or aggregated amylose sedimentation) were observed. According to their dynamic rheological properties, xanthan and mixed systems behave like viscoelastic fluids with xanthan dominating the overall behavior. Spectra obtained at various xanthan concentrations may be shifted along modulus and frequency axis for both salt conditions and the shift factors dependence on xanthan concentration is discussed.