Thermal degradation and stability of starch under different processing conditions

The objectives of this paper are to review the thermal degradation and stability of starch and starch-based materials, including both fundamental sciences such as detecting techniques, the effect of amylose/amylopectin content in starches and starches modifications, as well as the effect of different processing environments, such as an open or sealed system, and shearless or shear stress conditions. The decomposition temperature of starches was increased with increasing amylopectin content in an open system. In the open system, the initial water content did not affect the decomposition temperature because all water had evaporated from samples prior to reaching the decomposition temperature. Two decomposition temperatures were observed in the sealed system: the first at lower temperature represents long chain scission; and the second at higher temperature involves decomposition of glucose ring. In the sealed system, the first degradation was increased with increasing amylopectin content. There is no observable difference of the second degradation for the samples containing different amylose/amylopectin ratios. The higher the moisture content is, the lower the second decomposition temperature is detected in the sealed system. Significant shear degradation was observed in amylopectin component of starch, while high amylose starch proved less sensitive to shear stress. The achievements in this area have increased the knowledge of polymer science, in particular to understand the degradation of natural polymers.