Induced effects by oxidation with potassium permanganate on the thermal, morphological, colorimetric and pasting properties of corn starch.

Introduction. Native starches are the most consumed polysaccharides in human diet. They are used in several industries as food, textile, pharmaceutic, etc. However due to some limitations starches should be modified chemically. Materials and methods. Corn starch modified with standard solutions of potassium permanganate (KMnO4) was analysed by simultaneous thermogravimetry-differential thermal analysis, differential scanning calorimetry, rapid viscoamylographic analysis, field emission gun-scanning electron microscopy/energy dispersive spectroscopy, X-ray powder diffraction and colorimetric analysis. Results and discussion. Corn starch was oxidised with KMnO4 at different concentrations (0.01; 0.02 and 0.05 mol L-1) at pH = 6.0 for 1 hour. (0.01; 0.02 and 0.05 mol L-1), pH = 6.0 for 1 hour. After filtered, washed and dried at 40 oC by 24 hours, the properties of the samples were investigated. Thermogravimetric curves showed an endothermic peak attributed to evaporation of water and two exothermic peaks, which refer to the decomposition and oxidation of organic matter until the formation of ash. A period of stability was observed, which decrease after modification. The gelatinisation of oxidised starch occurred at higher peak temperatures and also required higher gelatinisation enthalpy. The viscosity of the samples was significantly reduced and the relative crystallinity increased in proportion to the oxidant concentration used. Manganese and potassium content increased with the modification. There were no morphological changes after oxidation; however a darkening of the samples was identified due to the presence of potassium and manganese observed by energy dispersive spectroscopy (EDS). Conclusions. The obtained fluid paste with low retrogradation tendency suggests the application of oxidised starch in the paper industry.