Tratamento físico e caracterização térmica, reológica e estrutural de amidos nativos e das misturas binárias de amidos de mandioca, batata doce e batata

Abstract

Native starches have limited features in terms of industrial use and they often need to be modified or treated. However, the use of chemicals is increasingly less preferred, in order to preserve human health and the environment. Therefore, the mixture of starch and physical treatment using heat and humidity can be a good alternative to the use of chemicals. The studied starches were from cassava, sweet potato and native potato; they were in binary mixtures in the ratios 1:1 and 1:2, except for the natives and mixtures (1:1), which were physically treated with heat and humidity in an autoclave at 121 °C for a period of 1 hour. Thermal study was performed on these samples using the techniques of thermogravimetry (TG) and derivative thermogravimetry (DTG), and differential scanning calorimetry (DSC). Rheological study was performed by rapid visco analysis (RVA) and structural study was performed by analysis of x-ray diffraction (XRD) and atomic force microscopy (AFM). From the TG and DTG curves, it was observed that both the native starches and the binary mixtures of these starches showed similar behaviour. For the samples that were treated physically, the values of weight loss during the phases of dehydration and oxidation decreased; the values increased during the decomposition phase. The potato starch showed the greatest enthalpy from the DSC results, as well as mixtures that contained potato starch. For treated starches, the temperatures at which the event occurred increased, and the higher the moisture levels of the treatment, the lower the enthalpy. The potato starch stood out in the AFM images, with larger diameter and roughness; the mixtures and the treated samples had brief alterations. For the native starches, and also the binary mixtures, the XRD peaks did not undergo pronounced displacement; for the treated samples there was a reduction in crystallinity. The native potato starch showed a higher peak viscosity, as well as the mixtures containing this starch. After physical treatment, the peak and final viscosities were reduced for all the samples.