Abstract:

Cassava starch was suspended at a concentration of 0.5 g/mL in 20% aqueous ethanol and then subjected to
microwave irradiation at 2 455 MHz. After different durations of microwave irradiation, the structure and properties of
cassava starch were examined by Fourier transform infrared spectrometer (FT-IR), ultraviolet visible spectrophotometer
(UV-Vis), scanning electron microscope (SEM), X-ray diffractometer (XRD), Ubbelohde viscometer and thermogravimetric
analyzer (TGA). It was suggested that new functional groups were not formed under the condition of microwave irradiation.
However, the intermolecular and intramolecular hydrogen bonds were altered. With increasing microwave irradiation
time, the maximum UV-Vis absorption wavelength and blue value of the starch-iodine complexes increased first and then
decreased. Much more concaves or ruffles on the surface of the starch granules were observed. Moreover, the XRD peak
intensity of cassava starch was enhanced by microwave irradiation. However, the crystal types of the starch granules were
not changed. Viscosity data demonstrated that intrinsic viscosity of the microwave irradiated-cassava starch displayed a
decreasing trend. Additionally, thermogravimetric analysis proved that the thermal stability of the starch was improved by
microwave irradiation.

Key words: microwave irradiation, cassava starch, structural characterization, intrinsic viscosity, thermogravimetric analysis