Thermal degradation of starch sources: Green banana, potato, cassava, and corn - kinetic study by non-isothermal procedures

In this study, scanning electronic microscopy, X-ray diffraction, and thermogravimetric analysis were used in order to study the main characteristics of starch from green-banana, corn, potato, and cassava, and to analyze the process of thermal degradation of these starches. The Flynn-Wall-Ozawa and modified Coats-Redfern methods were used to determine the activation energy (E) of the degradation process, by using thermogravimetric data. These studies have shown that potato starch exhibited the highest activation energy values during the entire thermal degradation process while corn starch exhibited the lower values. Banana, corn, and potato starches showed that its activation energy was not dependent on the conversion extension, and therefore degradation corresponds to a simple process. In contrast, cassava starch showed that E was dependent of the conversion level, indicating that this degradation was more complex which involved more than one reaction. Potato and banana starches had higher values of the activation energy in its thermal degradation, which could be attributed to greater heterogeneity in granule sizes. Corn starch, which has small and homogeneous granules and major contents of the crystalline fractions, presented a lower activation energy in thermal degradation process.