Multi-scale structures of cassava and potato starch fractions varying in granule size

Large-, medium-, and small-sized granules were separated from cassava and potato starches. Fourier transform infrared spectroscopy, wide angle X-ray diffraction, small angle X-ray scattering, nuclear magnetic resonance and scanning electron microscope were used to investigate the supramolecular structures of cassava and potato starch fractions. The crystallinity of small-sized potato starch (SPS) was lower than that of its counterparts, while crystallinities of all cassava fractions were similar. The contents of lamellar structure of small-sized granules were the smallest, while those of their counterparts were similar. The lamellar repeat distance was similar for the starch fractions. Self-similar structure of SPS showed mass fractal with the lowest compactness, while that of small-sized corn starch showed surface fractal with the largest compactness. The NMR test revealed that SPS had the highest total double helix content, while its counterparts showed similar values. Moreover, a new 13C peak at 64 ppm was observed for SPS.