Physicochemical properties of corn starch affected by the separation of granule shells

The physicochemical properties of corn starch (CS) and a component of granule shells (C_s) obtained through a granule shells separation process, were studied. The shells separation was accurately visualized and confirmed by SEM and TEM images. Both CS and C_s contained three components (amylopectin, intermediate fraction and amylose) with a M_w ranging from 4.11 × 10⁷ to 11.42 × 10⁷ g/mol. The amylose content of CS and C_s was in the following order: C_s-83 > CS > C_s-69 > C_s-76. There were no significant differences observed between CS and C_s-83 for the dynamic modulus, apparent viscosity, peak viscosity and final viscosity, while C_s-69 and C_s-76 exhibited a decreasing trend. The DSC results revealed that the transition temperatures of CS were significantly higher than those of C_s. There was an obvious decrease in the thermal degradation onset temperature (T_o) for the treated samples (CS:312.26 °C, C_s-69: 311.87 °C, C_s-76: 307.62 °C and C_s-83: 307.11 °C). The crystalline patterns of CS were converted from A-type to C-type during the granule shells separation process. The relative crystallinities of C_s were significantly lower than that of CS (26.87%). The FTIR results showed that intramolecular and intermolecular hydrogen-bonding (OH) of C_s were weakened after shells separation treatment.