Supramolecular structure and thermal behavior of cassava starch treated by oxygen and helium glow-plasmas

The thermal property of cassava starch was regulated by the oxygen or helium glow-plasma treatment to change its supramolecular hierarchical structure. By investigating the microstructural and mesoscopic scale structural alterations and the thermal transition without and with the glow-plasma treatment, the underlying mechanism was explored through establishing a structure-thermal property relationship. Particularly, while there were negligible changes to the granule morphology, the glow-plasma predominantly disorganized the crystallites with low perfection and thermal stability, resulting in decreased alignment of double-helices within the crystalline lamellae, reduced relative crystallinity and thermal transition enthalpy, and increased transition temperatures accompanied by a narrowed gelatinization temperature range. The thermal transition parameters could be further modulated by simply changing the atmosphere type and treatment time. This is much different from our previous study which showed if glow-plasma disrupted the supramolecular structure of starch, the thermal transition temperatures would be reduced. These findings from present study indicate that the glow-plasma treatment can serve as a highly-safe physical method to rationally regulate the hierarchical structure of cassava starch and thus to realize the development of starch-based products with desired thermal behavior. Industrial relevance Glow-plasma is a non-thermal physical technique and has gain huge interest in polymer modification due to the concerns over generated wastes and safety issues resulting from chemical modification. As the major storage carbohydrate in higher plants, starch is one of the most important raw materials for food and non-food industries. To improve the performance of starch and extend its applications, it is indispensible to understand how a specific technique alters the structure-property of starch. Regarding this, the present work revealed that the oxygen or helium glow-plasma preferably disorganized the crystallites of cassava starch with low perfection and thermal stability, which resulted in decreases in the relative crystallinity and the transition enthalpy but increases in the transition temperatures together with a narrowed transition temperature range. The thermal behavior of cassava starch could be further regulated by changing the gas type and the treatment time. These findings are much different from a previous work which showed if glow-plasma disorganized the supramolecular structure of starch, its thermal transition temperatures would be reduced. Hence, this study enables an understanding of how glow-plasma modulates the thermal property of cassava starch from a structural view, which is of value for rationally using glow-plasma as a new method to regulate the thermal transition of starch, for the production of starchy food products with desired thermal behavior.