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In this work the rheological behavior of manioc starch (S) industrially modified and its blends with a xyloglucan (XG) in the presence of tetraborate (T) ions at pH 12 was described. At rotational measurements the viscosity values showed a good interaction between polysaccharides (20/5 g/l, respectively, to S and XG), which were highly modified by the presence of tetraborate (7 g/l) resulting in better pseudo or plasticity. To system S/XG/T at 20/5/7 or 40/10/14 g/l the rheological properties were dependent of polysaccharides/T concentration. Mixtures at 25/7 g/l performed a viscoelastic solution, and at 50/14 g/l a weak gel. After the temperature sweep analyses (heating and cooling), a more solid character was obtained. This performance could be explained as a result of total gelatinization process that benefits the structural reorganization and better interaction between polysaccharides and the tetraborate complex formed with the hydrocolloid. Also, it was observed that the S/XG/T system, after heating/cooling together with a shear stress, adopted a helical conformation similar to that obtained with amylose standard, since it was colored in blue with lugol. So, the interactions are related with the conformational change of S and XG and also with shear processes, which aid the reptation phenomena and improvement of the solid character. |
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