RESEARCH ARTICLE Thermal degradation of starch sources: Green banana, potato, cassava, and corn – kinetic study by non-isothermal procedures Posidia Pineda-Go ´ mez 1,2 , Natalia C Angel-Gil 1 , Carolina Valencia-Mun ˜ oz 1 , Andres Rosales-Rivera 1 and Mario E Rodrı´guez-Garcı´a 3 1 Facultad de Ciencias Exactas y Naturales, Laboratorio de Magnetismo y Materiales Avanzados, Universidad Nacional de Colombia, Manizales, Caldas, Colombia 2 Universidad de Caldas, Manizales, Caldas, Colombia 3 Departamento de Nanotecnología, Centro de Física Aplica y Tecnología Avanzada, Universidad Nacional Autónoma de México, Quréretaro, Mexico 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. Received: September 24, 2013 Revised: January 22, 2014 Accepted: January 23, 2014 Keywords: Activation energy / Starch sources / Thermal degradation 1 Introduction Starch is a granular biopolymer of broad applications in both food-industrial and technological level. The largest propor- tion of the world’s production of starches from different sources is used in human and animal food, for their outstanding qualities as an adhesive, binder, film-former, foam stabilizer, gel, glaze, humectant, stabilizer, texturizer, and thicker. Currently starch is being used as feedstock in the chemical and pharmaceutical’s industry. Glucose obtained from starch is also used to obtain biofuels. Knowledge of the starch properties permits its application in various fields. The major constituents of starch granules are amylopectin and amylose. Amylopectin (75%) is a semi-crystalline highly branched polysaccharide with an a-1,4 backbone chains and 4–5% a-1,6 branch points enabling structuring of the starch granule while amylose (25%) is amorphous in the native starch granule and is composed of essentially linear chains of a-1,4 linked glucose units [1]. When starch is heated above 230°C it suffers decomposition. The degradation of polymer is a complex process; however, for practical engineering applications it may be sufficient to consider only the basic characteristics of the thermal decomposition process with some simplified mechanisms. Through kinet- ics’ studies, information about the mechanism’s reaction in a Colour online: See the article online to view Figs 2, 3, 5 and 6 in colour. Correspondence: Dr. Posidia Pineda-Gómez, Departamento de Física, Universidad de Caldas, Calle 65 No. 26–10, Apartado aéreo 275, Manizales, Caldas, Colombia E-mail: ppinedag@unal.edu.co Fax: þ57-6-8879495 Abbreviations: DTG, derivative TG curve; FWO, Flynn–Wall– Ozawa; TG, thermogravimetric; TGA, thermogravimetric analysis DOI 10.1002/star.201300210 Starch/Stärke 2014, 66,1–9 1 ß 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.starch-journal.com