Pasting and rheological properties of native and anionic tapioca starches as modified by guar gum and xanthan gum

Effects of guar and xanthan gums on pasting and rheological properties of native and anionic tapioca starches were studied by using a Rapid Visco-Analyzer (RVA), a differential scanning calorimeter (DSC), a scanning electron microscope (SEM), and a rheometer. Results of RVA measurement indicated that addition of gums increased peak, breakdown, and final viscosities of native tapioca starch. This effect was more pronounced for guar gum than xanthan gum. Setback viscosity was increased by guar gum, but xanthan gum showed the opposite effect. For anionic tapioca starch, addition of guar gum gave similar results whereas xanthan exhibited opposite results. Pasting temperatures of all samples with added gums increased in comparison with the controls which are in good agreement with the increments of the onset (T-o) and peak (T-p) gelatinization temperatures determined by the DSC. Reduction of gelatinization enthalpy (Delta H) with gums addition was also observed by the DSC. SEM micrographs reveal that only xanthan totally wrapped the native starch granules whereas the other starch-gum mixtures, gums did not wrap the granules. Measurement of swelling power (SP) demonstrated that the anionic starch exhibited higher SP than the native starch and addition of gums appeared to increase the SP values of the mixtures at high temperatures (> 80 degrees C). Results of dynamic viscoelasticity measurement indicated that addition of gums increased the G ' values two-fold at all frequencies tested, but the ratio G ''/G ' (tan delta) was decreased. This suggests that the starch-gum pastes behaved more solid-like characteristics than the starch alone pastes. (c) 2005 Elsevier Ltd. All rights reserved.