Structural characteristics and properties of starch granules in flue-cured tobacco leaves

Structure, crystalline and thermal properties of starch granules in matured tobacco leaves from Yunyan87, Zhongyan103 and Zhongyan202 were determined by environmental scanning electron microscope, X-ray diffractometer and simultaneous thermal analyzer. Results showed that most starch granules were spheroidal and long cylindrical, while others were irregular shape. The average diameter was 3 μm-4 μm. Layer structure was found on the surface of long cylindrical and irregular starch granules. The layer structure of Zhongyan103 and Zhongyan202 were more than Yunyan87. X-ray diffraction showed that relative crystallinities among three cultivars were significantly different, although they all showed B type diffraction spectrum. Thermal analysis showed that initial gelatinization temperature of starch granule was low, but peak temperature, terminal temperature and gelatinization enthalpy were high. There were no significant differences in gelatinization temperatures among cultivars. Gelatinization enthalpy decreased when relative crystallinity decreased.