The semi-crystalline growth rings of C-type pea starch granule revealed by SEM and HR-TEM during acid hydrolysis

Semi-crystalline growth rings and the crystalline lamella of C-type pea starch were studied by Scanning Electron Microscope (SEM) and Field Emission Gun Transmission Electron Microscope (FEG-TEM) during acid hydrolysis. The alternating growth rings (semi-crystalline and amorphous growth rings) are clearly observed under SEM. The thickness of semi-crystalline growth rings is variable and approximately 200 nm apart. SEM results also reveals that the amorphous areas mainly locate core part of C-type starch granules, while the crystalline areas mainly exist in the peripheral region of starch granules. The crystalline and the amorphous areas are hydrolyzed concomitantly, although slowly. The clear lattice fringes with different orientation corresponding to the different thickness of crystalline lamella were observable from high-resolution-TEM (HR-TEM) images. The crystalline lamella size can be confirmed to be about 20 nm with the length of 20 nm and the thickness of 20 nm. The clear lattice fringes should correspond to the crystalline phases in the semi-crystalline growth rings while the blurry regions correspond to the amorphous growth rings among the semi-crystalline growth rings.