Physicochemical and in vitro digestion of millet starch: Effect of moisture content in microwave

In this study, the physicochemical and in vitro digestion of millet starch with different moisture content after microwave treatment were investigated. The structure and property changes of native (NA) and microwave treated (MT) millet starches were characterized using Brabender viscometer, Fourier transforms infrared spectroscopy (FT-IR), Differential scanning calorimeter (DSC), X-ray diffraction (XRD) and Scanning electron microscopy (SEM). Microwave treatment caused a decrease of the peak viscosity, swelling power, ΔH and relative crystalline, and an increase of the transparency, TO, TC, and ΔT. The extent of these changes depended on the moisture content of starches. The in vitro enzymatic digestibility of samples increased greatly, especially at a moisture content of >40%. It is interesting to note that the peak of the hydroxyl group shifted toward the lower wavenumber direction and the decrease of peak intensities at 1047 cm-1 and 1022 cm-1 in FT-IR spectra indicated that higher moisture content enhanced the inter-molecular hydrogen bonding and caused more serious damage to the crystalline and amorphous regions. Cracks and center cavities were observed on the granules surface and the original appearance of starch disappeared gradually as the moisture content increases. In conclusion, high moisture content can enhance the effect of the microwave to millet starch.