Abstract:Nature corn starches treated by heat-moisture with water-ethanol mixtures were investigated in terms of polarization cross, morphology, size distribution, crystal structure and paste properties within the temperature range of 70~90 ℃. With the increase of the temperature in the treatment system, some phenomena were found as follows: the disappearance of the granules birefringence increased, and the granules broke in the end. The average radius of the starch granules was augmented from 23.6 μm to 50.4 μm and the amount of the small granules (<10 μm) decreased. Besides, the number of the medium granules (10~30 μm) and large granules (30~100 μm) increased in different degrees. Small holes and pits were observed on the surface of the granule, and the granules conglobated at high temperature in the end .After drying and grinding, the granules broke into flakes. X-ray diffraction intensity gradually reduced at the diffraction angle of 15°, 18° and 23°, but strengthened at 20°. Starting temperature of corn starch gelatinization raised from 80.5 ℃ to 90.6 ℃, and viscosity of the starch decreased, which indicated that the stability of both warm and cold paste improved while the retrogradation of the starch reduced. Determination of molecular weight of the starches displayed that molecular chains were ruptured and degraded during the heat-moisture treatment.
