Study on supramolecular structural changes of ultrasonic treated potato starch granules

The supramolecular structural features of ultrasonic treated potato starch granules in excess water were investigated. Various ultrasonic treatments were used; an ultrasound probe set with different power (60, 105, 155 W) at a frequency of 20 kHz for 30 min. Scanning electron microscopy (SEM) images show that ultrasonic treatment induced notch and groove on starch granule surface. The B-type crystal structure was scarcely affected according to polarized light microscopy (PLM) and X-ray diffraction (XRD) analysis. However, Small-angle X-ray scattering (SAXS) data manifest that fractal structures changed from surface fractal into mass fractal as the ultrasonic power increased, indicating that the compact starch granules swelled to a larger extent and loosed. The repeat cluster thickness was unchanged. The electron density contrast between the crystalline and the amorphous lamella decreased, while the electron density difference between the amorphous lamella and amylose background increased. Moreover, the molecular order in crystalline lamella was reduced. These results demonstrated that ultrasonic treatment affected cluster structure, especially the crystalline region, and amylose background was affected more compared to amylopectin amorphous lamella.