Pre-gelatinized tapioca starch and its mixtures with xanthan gum and ι-carrageenan

Heating of tapioca starch dispersions at low concentration (<10% w/w) forms highly viscous and translucent pastes. In this work, a completely cold soluble tapioca starch powder is produced by spray drying of a previously gelatinized starch paste. Rehydrating the powder yields a viscous paste with a loss in elasticity. Its combination with nongelling food hydrocolloids, such as xanthan gum or ι-carrageenan, restores the mechanical properties and creates alternative starch based thickening agents with a stable structure. Rotation and oscillatory rheological measurements show significant differences in viscosity–temperature, strain, and frequency dependence between the native tapioca starch paste and the spray dried one. The addition of xanthan gum or ι-carrageenan to the spray dried tapioca starch has a much stronger influence on its properties than their addition to the native starch. The different chain flexibilities of the polyelectrolytes cause disparate effects on the mechanical behavior of the mixed systems. By confocal laser scanning microscopy (CLSM) it is shown, that the mixture of starch and ι-carrageenan leads to a well-mixed phase with intermolecular interactions between the hydrocolloid and the starch molecules. In contrast, the addition of xanthan gum induces a separation into local micro domains resulting in a mutual exclusion, which is also confirmed by CLSM.