Morphology and physicochemical properties of mechanically activated rice starch

The morphology and physicochemical properties of mechanically activated rice starch (MARS) isolated from three rice cultivars were investigated by scanning electron microscopy, X-ray diffractometry, gel permeation chromatography and Rapid Visco Analysis. The shape of rice starch granule changed from native polyhedron to anomalistic state during mechanical activation. It was suggested that the hydration of starch and moisture was an important factor for granules agglomeration which appeared more easily with higher moisture content. Mechanical force resulted in destroying of starch crystal structure which disappeared basically after activated for 10 h. As the mechanical activation time prolonged, the amylopectin and amylose of rice starch were both decomposed gradually, thus causing the increase of cold-water solubility and reducing power and the decrease of BV. Meanwhile, the pasting temperature and the viscosity of MARS decreased, including peak viscosity, final viscosity, breakdown viscosity and setback viscosity. The crystalline and molecular structure of rice starch with 6.02% moisture content were more easily destroyed by mechanical force than those with 1.05% and 11.05% moisture content, which resulted in higher cold-water solubility and reducing power, lower BV, pasting temperature, peak viscosity, final viscosity, breakdown viscosity and setback viscosity.