Controlled fragmentation of starch into nanoparticles using a dry heating treatment under mildly acidic conditions

Normal corn starch was treated with acidic ethanol solution with various concentrations of ethanol (0, 10, 30, 50 and 95%) and acid (0.0026, 0.0053 and 0.0079 M) and then subjected to a dry heating treatment for 1, 2 and 4 h at 130 °C to prepare starch nanoparticles. Size of nanoparticles was determined using DLS (dynamic light scattering). FT-IR (Fourier-transform infrared spectroscopy), XRD (X-ray diffraction) and TEM (transmission electron microscopy) were used to determine the structure and morphology of starch nanoparticles. As the ethanol concentration decreased, the starch granule readily fragmented into smaller particles when simply dispersed in water, and this was possibly by the preferential hydrolysis of the starch chains in the amorphous region. A higher ethanol concentration (50 and 95%) did not produce homogenous nanoparticles, however 30% ethanol concentration produced uniform nanoparticles with a mean diameter of 46.4 nm. The treatment condition (30% ethanol) partially broke the long-range crystalline order but left the short range order of the spherical nanoparticles intact. However, lower ethanol (<30%) concentrations induced severe damages in the both crystalline structures (long and short range) of starch granule.