Effect of hydrolysis, phosphorylation and treatment with high hydrostatic pressure on thermal generation of stable and short-living radicals in maize starch was studied by X-ray diffraction (XRD), electron paramagnetic resonance (EPR) spectroscopy, differential scanning calorimetry and polarized light microscopy. Phosphorus was introduced into maize starch as monoand distarch phosphates. XRD indicated localization of phosphate groups in amorphous part of the granule whereas calorimetric data suggested some cross-linking of the distarch phosphates. Stable and short-living radicals with unpaired electron localized at carbon atom were generated in all investigated samples in the temperature range commonly used for processing food. The number of detected short-living radicals, stabilized by a spin trap, is of two orders of magnitude greater than that of the stable radical species. Hydrolysis and phosphorylation strongly increase the number of stable radicals while pretreatment of the starch with high hydrostatic pressure diminishes their amount. The EPR spectra of stable radicals consist of two components, single line and another one with hyperfine structure, indicating interaction of unpaired electron with neighboring hydrogen atom. The EPR spectra of the spin trap adducts with short-living radicals contain three components from species differing in their dynamic properties depending on localization in zones of various degree of crystallinity.
In this study, interactions of dichromate ions with potato starch granules in highly acidic aqueous solutions and at different temperatures were investigated. It was found that the process underwent a reduction of Cr(2)O(7)(2-) to Cr(3+) accompanied by the formation of intermediate Cr(5+) ions detected by electron paramagnetic resonance (EPR) spectroscopy. The reactions took place after the attachment of dichromate anions to the granules and resulted in a lowering of the Cr(2)O(7)(2-) initial content in the solution. The newly formed Cr(3+) ions were both accumulated by the granules or remained in the solution. It was observed for the first time that the quantity of such ions taken by the granules from the solution was noticeably higher than that delivered by trivalent chromium salt solution. It was revealed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX) that the chromium ions were not only adsorbed on the granule surface but also introduced into the granule interior and evenly distributed there. An activation energy of the reduction reaction equal to 65 kJ·mol(-1) and the optimal parameters of the process were established. The proposed mechanism could be useful for the bioremediation of industrial effluents polluted by hexavalent chromium compounds.
Starch is a biopolymer that is valuable in a number of industrial applications. However, chemical and physical modifications are required to improve its functionality. This study concerns the effect of the starch phosphorylation on its interactions with Cr(VI) ions in acidic aqueous solutions. An acidic medium (pH = 1) is necessary for effective reduction of Cr(VI) to Cr(III) and Cr(V), followed by cation adsorption to starch grains. The quantity of introduced phosphorous is determined by UV‐Vis spectroscopy, whereas the final amounts of adsorbed Cr(III) and Cr(V) ions are measured by quantitative analysis of EPR spectra. The effect of phosphorylation on the native starch structure is investigated by SEM and XRD, while starch surface properties are assessed by zeta potential measurements. The EPR measurements show that the number of Cr(III) ions adsorbed on phosphorylated starch corresponds exactly to the total number of incorporated PO43− groups – an amount superior to that of native starch. Thus, these phosphate groups act as very active adsorption centers for reduced chromium species. Ultimately, phosphorylated starch may be used to remove hazardous hexavalent chromium ions from industrial waste.
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