Understanding the destructuration of starch in water-ionic liquid mixtures

The destructuration of native maize starch in mixtures of water and ionic liquids (ILs) containing acetate anions was studied in dynamic heating conditions, combining calorimetry, rheology, microscopy and chromatographic techniques. A phase diagram of starch in water-IL solutions was established. The phase transitions undergone by starch include the typical endothermic gelatinization phenomenon for IL-water ratios lower than 0.5, while for mixtures with a higher ionic liquid content, a complex exothermic phenomenon combining mild degradation and solubilization takes place. This results in an optimum destructuration temperature as low as 40-50 °C for an IL-water ratio close to 0.7. In addition, specific macromolecular chain breaking reactions appear to take place, depending on the nature of the cations present, resulting in different macromolecular structures of the recovered starch. These results suggest the possibility of using solvent media design for a controlled modification of starch macromolecular characteristics.