Changes in crystalline structure of microspheres of corn starch and amylose under isothermal and temperature cycling treatments

Microspheres of corn starch and amylose were prepared by precipitating starch paste solution with absolute ethanol. The V-type crystalline structure was observed in the obtained microspheres. By storing the microspheres at three temperature conditions under 95% RH, constant temperatures at 8 °C and 30 °C as well as temperature cycles at 8 °C for 1 day and at 30 °C for 1 day, for different periods of time, changes in crystalline structure of the microspheres were investigated by X-ray diffraction (XRD) analysis. The results showed that the diffraction peaks of V-type crystalline structure vanished after the temperature treatments. Retrogradation yielding A-type crystalline structure took place in all the corn starch microspheres and only the amylose microspheres with 8 °C/30 °C treatment. Comparing with the isothermal treatments, the temperature cycling accelerated retrogradation of the microspheres.