Long-term annealing of C-type kudzu starch: Effect on crystalline type and other physicochemical properties

Kudzu starch samples were prepared by annealing (ANN) treatment in 1:1.5 starch to water ratio at 50 °C for 1, 3, and 9 days. The effects of ANN on the morphology, structure, swelling power, solubility, and pasting properties of the resultant samples were evaluated. Scanning electron microscopy showed that the surface of the starch granules was rougher with clear grooves after ANN treatment compared with the native starch granules. ANN resulted in leaching of some amylose molecules, but had slight effect on relative crystallinity. The increase in proportion of B-type polymorphs within the C-type kudzu starch was due to a polymorphic transition from A- to B-type resulting from ANN. ANN decreased the swelling power and the solubility of the kudzu starch subjected to heating from 50 to 90 °C. Differential scanning calorimetry indicated that ANN treatment increased the thermal transition temperatures as well as gelatinization enthalpy change values, but narrowed the range of gelatinization temperature. Moreover, rapid visco-analyzer data revealed that ANN increased the pasting temperature, but decreased the pasting viscosities.